Thread: Index creation takes for ever
Hi every one,
I've tried to reindex one of my customer's table to gain some disk space.
I had to stop after 90 m cpu...
I've then pg_dump'ed the database and recreate an other both on 7.3.4 and
7.4b
Both are still running after more than 30 minutes of CPU (100% cpu taken)
creating the levt_lu_ligne_evt_key.
Disks don't do anything, just cpu.
Here are the info I have
test=# \d ligneevt Table "public.ligne_evt" Column | Type |
Modifiers
-----------------+--------------------------+-----------------------------------
-------------levt_cod | integer | not null default nextval('seq_levt
_cod'::text)levt_tevt_cod | integer | not nulllevt_date | timestamp with time zone | not
nulllevt_type_per1 | integer | not nulllevt_perso_cod1 | integer | not
nulllevt_type_per2 | integer |levt_perso_cod2 | integer |levt_texte | text
|levt_lu | character varying(2) | default 'N'levt_visible | character varying(2)
|levt_attaquant | integer |levt_cible | integer |
Indexes: ligne_evt_pkey primary key btree (levt_cod), levt_attaquant_ligne_evt_key btree (levt_attaquant),
levt_cible_ligne_evt_key btree (levt_cible), levt_lu_ligne_evt_key btree (levt_lu),
levt_visible_ligne_evt_keybtree (levt_visible), ligne_evt_levt_cod_key btree (levt_cod),
ligne_evt_levt_date_keybtree (levt_date), ligne_evt_levt_perso_cod1_key btree (levt_perso_cod1),
ligne_evt_levt_perso_cod2_keybtree (levt_perso_cod2), ligne_evt_levt_tevt_cod_key btree (levt_tevt_cod),
ligne_evt_levt_type_per1_keybtree (levt_type_per1), ligne_evt_levt_type_per2_key btree (levt_type_per2)
Triggers: RI_ConstraintTrigger_5453038
test=# SELECT count(*) from ligne_evt ;count
--------230670
(1 row)
test=# SELECT levt_lu,count(*) from ligne_evt group by levt_lu;levt_lu | count
---------+--------N | 49435O | 181242
(2 rows)
Can some one help me?
Regards
--
Olivier PRENANT Tel: +33-5-61-50-97-00 (Work)
6, Chemin d'Harraud Turrou +33-5-61-50-97-01 (Fax)
31190 AUTERIVE +33-6-07-63-80-64 (GSM)
FRANCE Email: ohp@pyrenet.fr
------------------------------------------------------------------------------
Make your life a dream, make your dream a reality. (St Exupery)
ohp@pyrenet.fr writes:
> I've then pg_dump'ed the database and recreate an other both on 7.3.4 and
> 7.4b
> Both are still running after more than 30 minutes of CPU (100% cpu taken)
> creating the levt_lu_ligne_evt_key.
That's hard to believe. I get
regression=# SELECT levt_lu,count(*) from ligne_evt group by levt_lu;levt_lu | count
---------+--------N | 49435O | 181242
(2 rows)
Time: 6927.28 ms
regression=# create index levt_lu_ligne_evt_key on ligne_evt (levt_lu);
CREATE INDEX
Time: 14946.74 ms
on a not-very-fast machine ... and it seems to be mostly I/O bound.
What platform are you on? I could believe that the local qsort() is
incredibly inefficient with many equal keys. Another possibility is
that you're using a non-C locale and strcoll() is horribly slow.
regards, tom lane
Hi Tom, This is on unixware 7 (both 7.3.4 and 7.4b) I'm on the FR language (I'll re-initdb whith lang=C to see what happens) But I never had a problem before. Waiting for a reply, I drop the table after copying it, and arranged sql script to create the indexes BEFORE the COPY The overall process took only 5 Min. On Thu, 28 Aug 2003, Tom Lane wrote: > Date: Thu, 28 Aug 2003 10:13:21 -0400 > From: Tom Lane <tgl@sss.pgh.pa.us> > To: ohp@pyrenet.fr > Cc: pgsql-hackers list <pgsql-hackers@postgresql.org> > Subject: Re: [HACKERS] Index creation takes for ever > > ohp@pyrenet.fr writes: > > I've then pg_dump'ed the database and recreate an other both on 7.3.4 and > > 7.4b > > > Both are still running after more than 30 minutes of CPU (100% cpu taken) > > creating the levt_lu_ligne_evt_key. > > That's hard to believe. I get > > regression=# SELECT levt_lu,count(*) from ligne_evt group by levt_lu; > levt_lu | count > ---------+-------- > N | 49435 > O | 181242 > (2 rows) > > Time: 6927.28 ms > regression=# create index levt_lu_ligne_evt_key on ligne_evt (levt_lu); > CREATE INDEX > Time: 14946.74 ms > > on a not-very-fast machine ... and it seems to be mostly I/O bound. > > What platform are you on? I could believe that the local qsort() is > incredibly inefficient with many equal keys. Another possibility is > that you're using a non-C locale and strcoll() is horribly slow. > > regards, tom lane > -- Olivier PRENANT Tel: +33-5-61-50-97-00 (Work) 6, Chemin d'Harraud Turrou +33-5-61-50-97-01 (Fax) 31190 AUTERIVE +33-6-07-63-80-64 (GSM) FRANCE Email: ohp@pyrenet.fr ------------------------------------------------------------------------------ Make your life a dream, make your dream a reality. (St Exupery)
ohp@pyrenet.fr writes:
> This is on unixware 7 (both 7.3.4 and 7.4b)
> I'm on the FR language (I'll re-initdb whith lang=C to see what happens)
Okay. If you find it's still slow in C locale, the next thing to try
would be forcing use of our own qsort, as we already do for Solaris.
You'd need to tweak this bit in configure.in:
# Solaris has a very slow qsort in certain cases, so we replace it.
case $host_os in solaris*)
AC_LIBOBJ(qsort) ;;
esac
I'm not sure why it's done that way though. 'Twould be better to let
the per-platform template files determine it.
regards, tom lane
Okay, so far, I've reinitdb (on 7.4b) with LANG=C and it worked. So I reinitDB with LANG=FR and used LANG=C to psql -f xxx.sql template1 to recreate the db and it worked too... I did'nt initdb between cvs changes, maybe that's why. 7.4b seems ok. However, is there a way I can reindex on my 7.3.4 production cluster cluster without an initdb? would LANG=C psql -c"reindex table blah" db would help? On Thu, 28 Aug 2003, Tom Lane wrote: > Date: Thu, 28 Aug 2003 10:38:26 -0400 > From: Tom Lane <tgl@sss.pgh.pa.us> > To: ohp@pyrenet.fr > Cc: pgsql-hackers list <pgsql-hackers@postgresql.org> > Subject: Re: [HACKERS] Index creation takes for ever > > ohp@pyrenet.fr writes: > > This is on unixware 7 (both 7.3.4 and 7.4b) > > > I'm on the FR language (I'll re-initdb whith lang=C to see what happens) > > Okay. If you find it's still slow in C locale, the next thing to try > would be forcing use of our own qsort, as we already do for Solaris. > You'd need to tweak this bit in configure.in: > > # Solaris has a very slow qsort in certain cases, so we replace it. > case $host_os in solaris*) > AC_LIBOBJ(qsort) ;; > esac > > I'm not sure why it's done that way though. 'Twould be better to let > the per-platform template files determine it. > > regards, tom lane > -- Olivier PRENANT Tel: +33-5-61-50-97-00 (Work) 6, Chemin d'Harraud Turrou +33-5-61-50-97-01 (Fax) 31190 AUTERIVE +33-6-07-63-80-64 (GSM) FRANCE Email: ohp@pyrenet.fr ------------------------------------------------------------------------------ Make your life a dream, make your dream a reality. (St Exupery)
ohp@pyrenet.fr writes:
> I've reinitdb (on 7.4b) with LANG=C and it worked.
> So I reinitDB with LANG=FR and used LANG=C to psql -f xxx.sql template1 to
> recreate the db and it worked too...
That's weird. I don't understand why an initdb in the same locale would
make the problem go away.
> I did'nt initdb between cvs changes, maybe that's why.
If you had only seen the problem in 7.4b then I could believe that theory,
but since you also saw it in the stable 7.3 installation, I don't.
> would LANG=C psql -c"reindex table blah" db would help?
No, the LANG environment of psql wouldn't make the slightest difference
here.
I don't think you told us your platform? (OS version, kernel, compiler,
etc)
regards, tom lane
My platforms are Unixware 713. Am I right to be afraid that I have to pg_dump and reload? Stiil it's amazind, 7.3 has been up for months and I discover the proclem today... Well, I don't reindex that often... On Thu, 28 Aug 2003, Tom Lane wrote: > Date: Thu, 28 Aug 2003 12:19:13 -0400 > From: Tom Lane <tgl@sss.pgh.pa.us> > To: ohp@pyrenet.fr > Cc: pgsql-hackers list <pgsql-hackers@postgresql.org> > Subject: Re: [HACKERS] Index creation takes for ever > > ohp@pyrenet.fr writes: > > I've reinitdb (on 7.4b) with LANG=C and it worked. > > So I reinitDB with LANG=FR and used LANG=C to psql -f xxx.sql template1 to > > recreate the db and it worked too... > > That's weird. I don't understand why an initdb in the same locale would > make the problem go away. > > > I did'nt initdb between cvs changes, maybe that's why. > > If you had only seen the problem in 7.4b then I could believe that theory, > but since you also saw it in the stable 7.3 installation, I don't. > > > would LANG=C psql -c"reindex table blah" db would help? > > No, the LANG environment of psql wouldn't make the slightest difference > here. > > I don't think you told us your platform? (OS version, kernel, compiler, > etc) > > regards, tom lane > -- Olivier PRENANT Tel: +33-5-61-50-97-00 (Work) 6, Chemin d'Harraud Turrou +33-5-61-50-97-01 (Fax) 31190 AUTERIVE +33-6-07-63-80-64 (GSM) FRANCE Email: ohp@pyrenet.fr ------------------------------------------------------------------------------ Make your life a dream, make your dream a reality. (St Exupery)
Tom Lane wrote: > ohp@pyrenet.fr writes: > > This is on unixware 7 (both 7.3.4 and 7.4b) > > > I'm on the FR language (I'll re-initdb whith lang=C to see what happens) > > Okay. If you find it's still slow in C locale, the next thing to try > would be forcing use of our own qsort, as we already do for Solaris. > You'd need to tweak this bit in configure.in: > > # Solaris has a very slow qsort in certain cases, so we replace it. > case $host_os in solaris*) > AC_LIBOBJ(qsort) ;; > esac > > I'm not sure why it's done that way though. 'Twould be better to let > the per-platform template files determine it. The macro has to be in the configure.in file, but we could flag whether the macro should be used in the template file. I have avoided adding a variable just for one platform because it just adds an extra level of abstraction for little benefit. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania19073
Thanks to evryone that help on this one. I reinitdb --locale=C and reloaded everything today. That did the trick. However, is there a way to test that strcol is really the culprit? On Sat, 30 Aug 2003, Bruce Momjian wrote: > Date: Sat, 30 Aug 2003 11:11:11 -0400 (EDT) > From: Bruce Momjian <pgman@candle.pha.pa.us> > To: Tom Lane <tgl@sss.pgh.pa.us> > Cc: ohp@pyrenet.fr, pgsql-hackers list <pgsql-hackers@postgresql.org> > Subject: Re: [HACKERS] Index creation takes for ever > > Tom Lane wrote: > > ohp@pyrenet.fr writes: > > > This is on unixware 7 (both 7.3.4 and 7.4b) > > > > > I'm on the FR language (I'll re-initdb whith lang=C to see what happens) > > > > Okay. If you find it's still slow in C locale, the next thing to try > > would be forcing use of our own qsort, as we already do for Solaris. > > You'd need to tweak this bit in configure.in: > > > > # Solaris has a very slow qsort in certain cases, so we replace it. > > case $host_os in solaris*) > > AC_LIBOBJ(qsort) ;; > > esac > > > > I'm not sure why it's done that way though. 'Twould be better to let > > the per-platform template files determine it. > > The macro has to be in the configure.in file, but we could flag whether > the macro should be used in the template file. I have avoided adding a > variable just for one platform because it just adds an extra level of > abstraction for little benefit. > > -- Olivier PRENANT Tel: +33-5-61-50-97-00 (Work) 6, Chemin d'Harraud Turrou +33-5-61-50-97-01 (Fax) 31190 AUTERIVE +33-6-07-63-80-64 (GSM) FRANCE Email: ohp@pyrenet.fr ------------------------------------------------------------------------------ Make your life a dream, make your dream a reality. (St Exupery)
Tom, Let me come back on this one: I initdb --locale=C and reloaded all bases including this one. Index creation wassn't too bad. So I thought that was it. Yesturday evening I decided to make a test so I pg_dump'd that database, created a test db and reloaded evrything from the pg_dump. it took 69 minutes to finish, 75% of this time was devoted to create 2 indexes on varchar(2) with value being 'O', 'N' or null; I wonder if it's a configuration matter. PGSQL is VERY solicited here (10's thousand connections/day , multiple queries/connection Here's my postgresql.conf FWIW, Any advice ? # # PostgreSQL configuration file # ----------------------------- # # This file consists of lines of the form: # # name = value # # (The '=' is optional.) White space may be used. Comments are introduced # with '#' anywhere on a line. The complete list of option names and # allowed values can be found in the PostgreSQL documentation. The # commented-out settings shown in this file represent the default values. # # Any option can also be given as a command line switch to the # postmaster, e.g. 'postmaster -c log_connections=on'. Some options # can be changed at run-time with the 'SET' SQL command. # # This file is read on postmaster startup and when the postmaster # receives a SIGHUP. If you edit the file on a running system, you have # to SIGHUP the postmaster for the changes to take effect, or use # "pg_ctl reload". #======================================================================== # # Connection Parameters # tcpip_socket = true #ssl = false max_connections = 64 #superuser_reserved_connections = 2 port = 5432 hostname_lookup = true #show_source_port = false #unix_socket_directory = '' #unix_socket_group = '' #unix_socket_permissions = 0777 # octal #virtual_host = '' #krb_server_keyfile = '' # # Shared Memory Size # shared_buffers = 10000 # min max_connections*2 or 16, 8KB each max_fsm_relations = 1000 # min 10, fsm is free space map, ~40 bytes max_fsm_pages = 10000 # min 1000, fsm is free space map, ~6 bytes #max_locks_per_transaction = 64 # min 10 #wal_buffers = 8 # min 4, typically 8KB each # # Non-shared Memory Sizes # sort_mem = 10240 # min 64, size in KB #vacuum_mem = 8192 # min 1024, size in KB # # Write-ahead log (WAL) # #checkpoint_segments = 3 # in logfile segments, min 1, 16MB each #checkpoint_timeout = 300 # range 30-3600, in seconds # #commit_delay = 0 # range 0-100000, in microseconds #commit_siblings = 5 # range 1-1000 # #fsync = true #wal_sync_method = fsync # the default varies across platforms: # # fsync, fdatasync, open_sync, or open_datasync #wal_debug = 0 # range 0-16 # # Optimizer Parameters # #enable_seqscan = true #enable_indexscan = true #enable_tidscan = true #enable_sort = true #enable_nestloop = true #enable_mergejoin = true #enable_hashjoin = true effective_cache_size = 10000 # typically 8KB each #random_page_cost = 4 # units are one sequential page fetch cost #cpu_tuple_cost = 0.01 # (same) #cpu_index_tuple_cost = 0.001 # (same) #cpu_operator_cost = 0.0025 # (same) #default_statistics_target = 10 # range 1-1000 # # GEQO Optimizer Parameters # #geqo = true #geqo_selection_bias = 2.0 # range 1.5-2.0 #geqo_threshold = 11 #geqo_pool_size = 0 # default based on tables in statement, # range 128-1024 #geqo_effort = 1 #geqo_generations = 0 #geqo_random_seed = -1 # auto-compute seed # # Message display # #server_min_messages = notice # Values, in order of decreasing detail: # debug5, debug4, debug3, debug2,debug1, # info, notice, warning, error, log, fatal, # panic #client_min_messages = notice # Values, in order of decreasing detail: # debug5, debug4, debug3, debug2,debug1, # log, info, notice, warning, error #silent_mode = false log_connections = true log_pid = true log_statement = true log_duration = true #log_timestamp = false #log_min_error_statement = error # Values in order of increasing severity: # debug5, debug4, debug3, debug2,debug1, # info, notice, warning, error, panic(off) #debug_print_parse = false #debug_print_rewritten = false #debug_print_plan = false debug_pretty_print = false #explain_pretty_print = true # requires USE_ASSERT_CHECKING #debug_assertions = true # # Syslog # syslog = 2 # range 0-2 #syslog_facility = 'LOCAL0' #syslog_ident = 'postgres' # # Statistics # #show_parser_stats = false #show_planner_stats = false #show_executor_stats = false #show_statement_stats = false # requires BTREE_BUILD_STATS #show_btree_build_stats = false # # Access statistics collection # #stats_start_collector = true #stats_reset_on_server_start = true stats_command_string = true stats_row_level = true #stats_block_level = false # # Lock Tracing # #trace_notify = false # requires LOCK_DEBUG #trace_locks = false #trace_userlocks = false #trace_lwlocks = false #debug_deadlocks = false #trace_lock_oidmin = 16384 #trace_lock_table = 0 # # Misc # #autocommit = true #dynamic_library_path = '$libdir' #search_path = '$user,public' datestyle = 'postgres, european' #timezone = unknown # actually, defaults to TZ environment setting #australian_timezones = false #client_encoding = sql_ascii # actually, defaults to database encoding #authentication_timeout = 60 # 1-600, in seconds #deadlock_timeout = 1000 # in milliseconds #default_transaction_isolation = 'read committed' #max_expr_depth = 10000 # min 10 #max_files_per_process = 1000 # min 25 #password_encryption = true #sql_inheritance = true #transform_null_equals = false #statement_timeout = 0 # 0 is disabled, in milliseconds #db_user_namespace = false # # Local Settings LC_MESSAGES = 'fr_FR' LC_MONETARY = 'fr_FR' The machine has 1 G DDR ECC Registred RAM, 2 1,8 GZ XEON running uw713 PGversion is 7.3.4, macine is not swaping. Those index creation took 100% of 1 CPU. Regards On Thu, 28 Aug 2003, Tom Lane wrote: > Date: Thu, 28 Aug 2003 10:13:21 -0400 > From: Tom Lane <tgl@sss.pgh.pa.us> > To: ohp@pyrenet.fr > Cc: pgsql-hackers list <pgsql-hackers@postgresql.org> > Subject: Re: [HACKERS] Index creation takes for ever > > ohp@pyrenet.fr writes: > > I've then pg_dump'ed the database and recreate an other both on 7.3.4 and > > 7.4b > > > Both are still running after more than 30 minutes of CPU (100% cpu taken) > > creating the levt_lu_ligne_evt_key. > > That's hard to believe. I get > > regression=# SELECT levt_lu,count(*) from ligne_evt group by levt_lu; > levt_lu | count > ---------+-------- > N | 49435 > O | 181242 > (2 rows) > > Time: 6927.28 ms > regression=# create index levt_lu_ligne_evt_key on ligne_evt (levt_lu); > CREATE INDEX > Time: 14946.74 ms > > on a not-very-fast machine ... and it seems to be mostly I/O bound. > > What platform are you on? I could believe that the local qsort() is > incredibly inefficient with many equal keys. Another possibility is > that you're using a non-C locale and strcoll() is horribly slow. > > regards, tom lane > -- Olivier PRENANT Tel: +33-5-61-50-97-00 (Work) 6, Chemin d'Harraud Turrou +33-5-61-50-97-01 (Fax) 31190 AUTERIVE +33-6-07-63-80-64 (GSM) FRANCE Email: ohp@pyrenet.fr ------------------------------------------------------------------------------ Make your life a dream, make your dream a reality. (St Exupery)
ohp@pyrenet.fr writes:
> it took 69 minutes to finish, 75% of this time was devoted to create 2
> indexes on varchar(2) with value being 'O', 'N' or null;
> I wonder if it's a configuration matter.
I still say it's either strcoll or qsort's fault. Try swapping in our
own version of qsort to see if the behavior changes.
regards, tom lane
Hi Tom, I've made some tests with your qsort and it DEFINITIVLY help ~3 mn instead of 69. However this is for 7.3.4 I've got no probs with 7.4b. Did something change in btree creation? On Mon, 1 Sep 2003, Tom Lane wrote: > Date: Mon, 01 Sep 2003 08:46:09 -0400 > From: Tom Lane <tgl@sss.pgh.pa.us> > To: ohp@pyrenet.fr > Cc: pgsql-hackers list <pgsql-hackers@postgresql.org> > Subject: Re: [HACKERS] Index creation takes for ever > > ohp@pyrenet.fr writes: > > it took 69 minutes to finish, 75% of this time was devoted to create 2 > > indexes on varchar(2) with value being 'O', 'N' or null; > > I wonder if it's a configuration matter. > > I still say it's either strcoll or qsort's fault. Try swapping in our > own version of qsort to see if the behavior changes. > > regards, tom lane > -- Olivier PRENANT Tel: +33-5-61-50-97-00 (Work) 6, Chemin d'Harraud Turrou +33-5-61-50-97-01 (Fax) 31190 AUTERIVE +33-6-07-63-80-64 (GSM) FRANCE Email: ohp@pyrenet.fr ------------------------------------------------------------------------------ Make your life a dream, make your dream a reality. (St Exupery)
ohp@pyrenet.fr writes:
> I've made some tests with your qsort and it DEFINITIVLY help
> ~3 mn instead of 69.
> However this is for 7.3.4 I've got no probs with 7.4b.
> Did something change in btree creation?
Hmm, I wouldn't have thought so, but perhaps we did change something
that would affect this. You might need to burrow down as far as seeing
exactly what qsort calls are being made in each version ...
regards, tom lane
On Mon, 01 Sep 2003 08:46:09 -0400, Tom Lane <tgl@sss.pgh.pa.us>
wrote:
>ohp@pyrenet.fr writes:
>> it took 69 minutes to finish, 75% of this time was devoted to create 2
>> indexes on varchar(2) with value being 'O', 'N' or null;
>
>I still say it's either strcoll or qsort's fault.
If qsort is to blame, then maybe this patch could help. It sorts
equal key values on item pointer. And if it doesn't help index
creation speed, at least the resulting index has better correlation.
Test script:
CREATE TABLE t (i int NOT NULL, t text NOT NULL);
INSERT INTO t VALUES (1, 'lajshdflasjhdflajhsdfljhasdlfjhasdf');
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t VALUES (100, 's,dmfa.,smdn.famsndfamdnsbfmansdbf');
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
INSERT INTO t SELECT * FROM t;
ANALYZE t;
CREATE INDEX t_i ON t(i);
SET enable_seqscan = 0;
SELECT ctid FROM t WHERE i=100 LIMIT 10;
Result without patch:
ctid
----------
(153,14)
(306,23)
(305,80)
(152,91)
(76,68)
(38,34)
(153,34)
(305,50)
(9,62)
(305,40)
(10 rows)
Result with patch:
ctid
--------
(0,5)
(0,10)
(0,15)
(0,20)
(0,25)
(0,30)
(0,35)
(0,40)
(0,45)
(0,50)
(10 rows)
For testing purposes I have made a second patch that provides a
boolean GUC variable sort_index. It is available here:
http://www.pivot.at/pg/23.test-IdxTupleSort.diff
Servus
Manfred
diff -ruN ../base/src/backend/utils/sort/tuplesort.c src/backend/utils/sort/tuplesort.c
--- ../base/src/backend/utils/sort/tuplesort.c 2003-08-17 21:58:06.000000000 +0200
+++ src/backend/utils/sort/tuplesort.c 2003-09-05 10:04:22.000000000 +0200
@@ -2071,6 +2071,33 @@
(errcode(ERRCODE_UNIQUE_VIOLATION),
errmsg("could not create unique index"),
errdetail("Table contains duplicated values.")));
+ else
+ {
+ /*
+ * If key values are equal, we sort on ItemPointer. This might help
+ * for some bad qsort implementation having performance problems
+ * with many equal items. OTOH I wouldn't trust such a weak qsort
+ * to handle pre-sorted sequences very well ...
+ *
+ * Anyway, this code doesn't hurt much, and it helps produce indices
+ * with better index correlation which is a good thing per se.
+ */
+ ItemPointer tid1 = &tuple1->t_tid;
+ ItemPointer tid2 = &tuple2->t_tid;
+ BlockNumber blk1 = ItemPointerGetBlockNumber(tid1);
+ BlockNumber blk2 = ItemPointerGetBlockNumber(tid2);
+
+ if (blk1 != blk2)
+ return (blk1 < blk2) ? -1 : 1;
+ else
+ {
+ OffsetNumber pos1 = ItemPointerGetOffsetNumber(tid1);
+ OffsetNumber pos2 = ItemPointerGetOffsetNumber(tid2);
+
+ if (pos1 != pos2)
+ return (pos1 < pos2) ? -1 : 1;
+ }
+ }
return 0;
}
I assume this completes this TODO:
* Order duplicate index entries by tid for faster heap lookups
and you will submit it for 7.5? If you want to post it now, I can get
it into the 7.5 queue so we don't forget it.
---------------------------------------------------------------------------
Manfred Koizar wrote:
> On Mon, 01 Sep 2003 08:46:09 -0400, Tom Lane <tgl@sss.pgh.pa.us>
> wrote:
> >ohp@pyrenet.fr writes:
> >> it took 69 minutes to finish, 75% of this time was devoted to create 2
> >> indexes on varchar(2) with value being 'O', 'N' or null;
> >
> >I still say it's either strcoll or qsort's fault.
>
> If qsort is to blame, then maybe this patch could help. It sorts
> equal key values on item pointer. And if it doesn't help index
> creation speed, at least the resulting index has better correlation.
>
> Test script:
> CREATE TABLE t (i int NOT NULL, t text NOT NULL);
> INSERT INTO t VALUES (1, 'lajshdflasjhdflajhsdfljhasdlfjhasdf');
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t VALUES (100, 's,dmfa.,smdn.famsndfamdnsbfmansdbf');
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> ANALYZE t;
> CREATE INDEX t_i ON t(i);
> SET enable_seqscan = 0;
> SELECT ctid FROM t WHERE i=100 LIMIT 10;
>
> Result without patch:
> ctid
> ----------
> (153,14)
> (306,23)
> (305,80)
> (152,91)
> (76,68)
> (38,34)
> (153,34)
> (305,50)
> (9,62)
> (305,40)
> (10 rows)
>
> Result with patch:
> ctid
> --------
> (0,5)
> (0,10)
> (0,15)
> (0,20)
> (0,25)
> (0,30)
> (0,35)
> (0,40)
> (0,45)
> (0,50)
> (10 rows)
>
> For testing purposes I have made a second patch that provides a
> boolean GUC variable sort_index. It is available here:
> http://www.pivot.at/pg/23.test-IdxTupleSort.diff
>
> Servus
> Manfred
> diff -ruN ../base/src/backend/utils/sort/tuplesort.c src/backend/utils/sort/tuplesort.c
> --- ../base/src/backend/utils/sort/tuplesort.c 2003-08-17 21:58:06.000000000 +0200
> +++ src/backend/utils/sort/tuplesort.c 2003-09-05 10:04:22.000000000 +0200
> @@ -2071,6 +2071,33 @@
> (errcode(ERRCODE_UNIQUE_VIOLATION),
> errmsg("could not create unique index"),
> errdetail("Table contains duplicated values.")));
> + else
> + {
> + /*
> + * If key values are equal, we sort on ItemPointer. This might help
> + * for some bad qsort implementation having performance problems
> + * with many equal items. OTOH I wouldn't trust such a weak qsort
> + * to handle pre-sorted sequences very well ...
> + *
> + * Anyway, this code doesn't hurt much, and it helps produce indices
> + * with better index correlation which is a good thing per se.
> + */
> + ItemPointer tid1 = &tuple1->t_tid;
> + ItemPointer tid2 = &tuple2->t_tid;
> + BlockNumber blk1 = ItemPointerGetBlockNumber(tid1);
> + BlockNumber blk2 = ItemPointerGetBlockNumber(tid2);
> +
> + if (blk1 != blk2)
> + return (blk1 < blk2) ? -1 : 1;
> + else
> + {
> + OffsetNumber pos1 = ItemPointerGetOffsetNumber(tid1);
> + OffsetNumber pos2 = ItemPointerGetOffsetNumber(tid2);
> +
> + if (pos1 != pos2)
> + return (pos1 < pos2) ? -1 : 1;
> + }
> + }
>
> return 0;
> }
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: you can get off all lists at once with the unregister command
> (send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> I assume this completes this TODO:
> * Order duplicate index entries by tid for faster heap lookups
I don't know why that TODO entry exists, but I think the idea is
counterproductive. The existing btree code will tend to put newer
versions of a row earlier (because it puts a new entry in front of any
with duplicate keys), which usually reduces the time spent skipping dead
rows. Forcing tid ordering will cost us more in dead-row skipping than
it's likely to save elsewhere.
regards, tom lane
Tom Lane wrote: > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > I assume this completes this TODO: > > * Order duplicate index entries by tid for faster heap lookups > > I don't know why that TODO entry exists, but I think the idea is > counterproductive. The existing btree code will tend to put newer > versions of a row earlier (because it puts a new entry in front of any > with duplicate keys), which usually reduces the time spent skipping dead > rows. Forcing tid ordering will cost us more in dead-row skipping than > it's likely to save elsewhere. I assume you are talking about a unique index that probably only has a few non-expired rows (in which case the newer rows first is better). The TODO deals with cases where you have lots of valid duplicate index rows, and you want to spin through all the matching rows in heap order rather than randomly. This is related to our CLUSTER capability. The idea originally came from Vadim. At what point does this patch do the sorting? -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Tom Lane wrote:
>>> * Order duplicate index entries by tid for faster heap lookups
>
>> I don't know why that TODO entry exists, but I think the idea is
>> counterproductive.
> I assume you are talking about a unique index that probably only has a
> few non-expired rows (in which case the newer rows first is better).
> The TODO deals with cases where you have lots of valid duplicate index
> rows, and you want to spin through all the matching rows in heap order
> rather than randomly.
Maybe so, but it would degrade the performance in the unique-index case
if we do it as the TODO is worded.
My own opinion is that the bitmap-index-lookup approach will be superior
to trying to keep the index entries in TID order. (That's the idea
we've been discussing for awhile of separating the heap-fetch stage from
the index-scan stage: scan the index, make a sparse bitmap of the TIDs
we need to visit, possibly AND or OR this bitmap with maps derived from
other indexes, and finally visit the rows in heap order.)
regards, tom lane
Tom Lane wrote: > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > Tom Lane wrote: > >>> * Order duplicate index entries by tid for faster heap lookups > > > >> I don't know why that TODO entry exists, but I think the idea is > >> counterproductive. > > > I assume you are talking about a unique index that probably only has a > > few non-expired rows (in which case the newer rows first is better). > > The TODO deals with cases where you have lots of valid duplicate index > > rows, and you want to spin through all the matching rows in heap order > > rather than randomly. > > Maybe so, but it would degrade the performance in the unique-index case > if we do it as the TODO is worded. Yes, the wording is just a guide. > My own opinion is that the bitmap-index-lookup approach will be superior > to trying to keep the index entries in TID order. (That's the idea > we've been discussing for awhile of separating the heap-fetch stage from > the index-scan stage: scan the index, make a sparse bitmap of the TIDs > we need to visit, possibly AND or OR this bitmap with maps derived from > other indexes, and finally visit the rows in heap order.) Oh, yes. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
On Sun, 7 Sep 2003 11:43:42 -0400 (EDT), Bruce Momjian <pgman@candle.pha.pa.us> wrote: >I assume this completes this TODO: > > * Order duplicate index entries by tid for faster heap lookups I don't think so, because the patch does nothing to keep the sort order once the index is initially created. > If you want to post it now, [...] I did already post it. It's only the last page or so of the original message. The link in that message points to a testing aid which is not part of what I would like to see committed. Servus Manfred
On Sun, 07 Sep 2003 12:23:28 -0400, Tom Lane <tgl@sss.pgh.pa.us>
wrote:
>Maybe so, but it would degrade the performance in the unique-index case
>if we do it as the TODO is worded.
The patch would only hurt with a unique index, if there are lots of
duplicate tuples at CREATE INDEX time.
>My own opinion is that the bitmap-index-lookup approach will be superior
So is mine, but I was not able to do this in 30 lines. Sorry ;-)
>to trying to keep the index entries in TID order.
^^^^
... which the patch does not. I see its main advantage in creating
better b-tree indices when you restore a large database with many
duplicate index entries.
It is intended to be only effective at CREATE INDEX or REINDEX time.
I don't believe it is activated when you insert a single new entry,
otherwise it wouldn't pass regression tests ...
Servus
Manfred
Manfred Koizar wrote:
> On Sun, 7 Sep 2003 11:43:42 -0400 (EDT), Bruce Momjian
> <pgman@candle.pha.pa.us> wrote:
> >I assume this completes this TODO:
> >
> > * Order duplicate index entries by tid for faster heap lookups
>
> I don't think so, because the patch does nothing to keep the sort
> order once the index is initially created.
As Tom mentioned, we might not want to keep the tid's in order after the
index is created because he wants the most recent tid's first, so the
expired ones migrate to the end.
Seems this patch does what we want currently because it only affects the
initial index structure.
> > If you want to post it now, [...]
>
> I did already post it. It's only the last page or so of the original
> message. The link in that message points to a testing aid which is
> not part of what I would like to see committed.
OK, in 7.5 queue:
http:/momjian.postgresql.org/cgi-bin/pgpatches2
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
> > I don't think so, because the patch does nothing to keep the sort > > order once the index is initially created. > > As Tom mentioned, we might not want to keep the tid's in order after the > index is created because he wants the most recent tid's first, so the > expired ones migrate to the end. But on average this argument only holds true for unique indexes, no ? Is there any code that stops the heap lookup after the visible tuple is found ? At least in an index with more rows per key you will fetch all heaps after the first one anyway to get at the next row. This is better done in heap order, no ? And the bitmap approach will not work for large result sets. Summa summarum I would leave the TODO item (maybe add a comment (only for non-unique, evaluate performance)) Andreas
On Mon, 8 Sep 2003 11:31:05 +0200, "Zeugswetter Andreas SB SD" <ZeugswetterA@spardat.at> wrote: >> As Tom mentioned, we might not want to keep the tid's in order after the >> index is created because he wants the most recent tid's first, so the >> expired ones migrate to the end. > >But on average this argument only holds true for unique indexes, no ? >Is there any code that stops the heap lookup after the visible tuple is found ? >At least in an index with more rows per key you will fetch all heaps after the >first one anyway to get at the next row. This is better done in heap order, no ? Yes, yes, yes, and yes. Seems we all agree on that; the patch has been queued for 7.5. Servus Manfred
Your patch has been added to the PostgreSQL unapplied patches list at:
http://momjian.postgresql.org/cgi-bin/pgpatches
I will try to apply it within the next 48 hours.
---------------------------------------------------------------------------
Manfred Koizar wrote:
> On Mon, 01 Sep 2003 08:46:09 -0400, Tom Lane <tgl@sss.pgh.pa.us>
> wrote:
> >ohp@pyrenet.fr writes:
> >> it took 69 minutes to finish, 75% of this time was devoted to create 2
> >> indexes on varchar(2) with value being 'O', 'N' or null;
> >
> >I still say it's either strcoll or qsort's fault.
>
> If qsort is to blame, then maybe this patch could help. It sorts
> equal key values on item pointer. And if it doesn't help index
> creation speed, at least the resulting index has better correlation.
>
> Test script:
> CREATE TABLE t (i int NOT NULL, t text NOT NULL);
> INSERT INTO t VALUES (1, 'lajshdflasjhdflajhsdfljhasdlfjhasdf');
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t VALUES (100, 's,dmfa.,smdn.famsndfamdnsbfmansdbf');
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> INSERT INTO t SELECT * FROM t;
> ANALYZE t;
> CREATE INDEX t_i ON t(i);
> SET enable_seqscan = 0;
> SELECT ctid FROM t WHERE i=100 LIMIT 10;
>
> Result without patch:
> ctid
> ----------
> (153,14)
> (306,23)
> (305,80)
> (152,91)
> (76,68)
> (38,34)
> (153,34)
> (305,50)
> (9,62)
> (305,40)
> (10 rows)
>
> Result with patch:
> ctid
> --------
> (0,5)
> (0,10)
> (0,15)
> (0,20)
> (0,25)
> (0,30)
> (0,35)
> (0,40)
> (0,45)
> (0,50)
> (10 rows)
>
> For testing purposes I have made a second patch that provides a
> boolean GUC variable sort_index. It is available here:
> http://www.pivot.at/pg/23.test-IdxTupleSort.diff
>
> Servus
> Manfred
> diff -ruN ../base/src/backend/utils/sort/tuplesort.c src/backend/utils/sort/tuplesort.c
> --- ../base/src/backend/utils/sort/tuplesort.c 2003-08-17 21:58:06.000000000 +0200
> +++ src/backend/utils/sort/tuplesort.c 2003-09-05 10:04:22.000000000 +0200
> @@ -2071,6 +2071,33 @@
> (errcode(ERRCODE_UNIQUE_VIOLATION),
> errmsg("could not create unique index"),
> errdetail("Table contains duplicated values.")));
> + else
> + {
> + /*
> + * If key values are equal, we sort on ItemPointer. This might help
> + * for some bad qsort implementation having performance problems
> + * with many equal items. OTOH I wouldn't trust such a weak qsort
> + * to handle pre-sorted sequences very well ...
> + *
> + * Anyway, this code doesn't hurt much, and it helps produce indices
> + * with better index correlation which is a good thing per se.
> + */
> + ItemPointer tid1 = &tuple1->t_tid;
> + ItemPointer tid2 = &tuple2->t_tid;
> + BlockNumber blk1 = ItemPointerGetBlockNumber(tid1);
> + BlockNumber blk2 = ItemPointerGetBlockNumber(tid2);
> +
> + if (blk1 != blk2)
> + return (blk1 < blk2) ? -1 : 1;
> + else
> + {
> + OffsetNumber pos1 = ItemPointerGetOffsetNumber(tid1);
> + OffsetNumber pos2 = ItemPointerGetOffsetNumber(tid2);
> +
> + if (pos1 != pos2)
> + return (pos1 < pos2) ? -1 : 1;
> + }
> + }
>
> return 0;
> }
>
> ---------------------------(end of broadcast)---------------------------
> TIP 6: Have you searched our list archives?
>
> http://archives.postgresql.org
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
Bruce Momjian <pgman@candle.pha.pa.us> writes:
>> If qsort is to blame, then maybe this patch could help. It sorts
>> equal key values on item pointer. And if it doesn't help index
>> creation speed, at least the resulting index has better correlation.
> I will try to apply it within the next 48 hours.
I think this is a *very* dubious idea. It introduces a low-level
implementation dependency into our sort behavior on the strength of no
more than an unfounded speculation that some platform's broken qsort
might run faster. Even if the speculation were proven true, I'd be
hesistant to apply it.
regards, tom lane
Tom Lane wrote: > Bruce Momjian <pgman@candle.pha.pa.us> writes: > >> If qsort is to blame, then maybe this patch could help. It sorts > >> equal key values on item pointer. And if it doesn't help index > >> creation speed, at least the resulting index has better correlation. > > > I will try to apply it within the next 48 hours. > > I think this is a *very* dubious idea. It introduces a low-level > implementation dependency into our sort behavior on the strength of no > more than an unfounded speculation that some platform's broken qsort > might run faster. Even if the speculation were proven true, I'd be > hesistant to apply it. Roger --- patch removed. Thanks. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
Patch removed from queue. --------------------------------------------------------------------------- Manfred Koizar wrote: > On Mon, 01 Sep 2003 08:46:09 -0400, Tom Lane <tgl@sss.pgh.pa.us> > wrote: > >ohp@pyrenet.fr writes: > >> it took 69 minutes to finish, 75% of this time was devoted to create 2 > >> indexes on varchar(2) with value being 'O', 'N' or null; > > > >I still say it's either strcoll or qsort's fault. > > If qsort is to blame, then maybe this patch could help. It sorts > equal key values on item pointer. And if it doesn't help index > creation speed, at least the resulting index has better correlation. > > Test script: > CREATE TABLE t (i int NOT NULL, t text NOT NULL); > INSERT INTO t VALUES (1, 'lajshdflasjhdflajhsdfljhasdlfjhasdf'); > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t VALUES (100, 's,dmfa.,smdn.famsndfamdnsbfmansdbf'); > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > INSERT INTO t SELECT * FROM t; > ANALYZE t; > CREATE INDEX t_i ON t(i); > SET enable_seqscan = 0; > SELECT ctid FROM t WHERE i=100 LIMIT 10; > > Result without patch: > ctid > ---------- > (153,14) > (306,23) > (305,80) > (152,91) > (76,68) > (38,34) > (153,34) > (305,50) > (9,62) > (305,40) > (10 rows) > > Result with patch: > ctid > -------- > (0,5) > (0,10) > (0,15) > (0,20) > (0,25) > (0,30) > (0,35) > (0,40) > (0,45) > (0,50) > (10 rows) > > For testing purposes I have made a second patch that provides a > boolean GUC variable sort_index. It is available here: > http://www.pivot.at/pg/23.test-IdxTupleSort.diff > > Servus > Manfred > diff -ruN ../base/src/backend/utils/sort/tuplesort.c src/backend/utils/sort/tuplesort.c > --- ../base/src/backend/utils/sort/tuplesort.c 2003-08-17 21:58:06.000000000 +0200 > +++ src/backend/utils/sort/tuplesort.c 2003-09-05 10:04:22.000000000 +0200 > @@ -2071,6 +2071,33 @@ > (errcode(ERRCODE_UNIQUE_VIOLATION), > errmsg("could not create unique index"), > errdetail("Table contains duplicated values."))); > + else > + { > + /* > + * If key values are equal, we sort on ItemPointer. This might help > + * for some bad qsort implementation having performance problems > + * with many equal items. OTOH I wouldn't trust such a weak qsort > + * to handle pre-sorted sequences very well ... > + * > + * Anyway, this code doesn't hurt much, and it helps produce indices > + * with better index correlation which is a good thing per se. > + */ > + ItemPointer tid1 = &tuple1->t_tid; > + ItemPointer tid2 = &tuple2->t_tid; > + BlockNumber blk1 = ItemPointerGetBlockNumber(tid1); > + BlockNumber blk2 = ItemPointerGetBlockNumber(tid2); > + > + if (blk1 != blk2) > + return (blk1 < blk2) ? -1 : 1; > + else > + { > + OffsetNumber pos1 = ItemPointerGetOffsetNumber(tid1); > + OffsetNumber pos2 = ItemPointerGetOffsetNumber(tid2); > + > + if (pos1 != pos2) > + return (pos1 < pos2) ? -1 : 1; > + } > + } > > return 0; > } > > ---------------------------(end of broadcast)--------------------------- > TIP 6: Have you searched our list archives? > > http://archives.postgresql.org -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
On Mon, 1 Dec 2003 00:02:54 -0500 (EST), Bruce Momjian <pgman@candle.pha.pa.us> wrote: >Tom Lane wrote: >> Bruce Momjian <pgman@candle.pha.pa.us> writes: >> >> And if it doesn't help index >> >> creation speed, at least the resulting index has better correlation. ... which has been shown by the example in the original message: > Result without patch: > ctid > ---------- > (153,14) > (306,23) > (305,80) > (152,91) > (76,68) > (38,34) > (153,34) > (305,50) > (9,62) > (305,40) > (10 rows) > > Result with patch: > ctid > -------- > (0,5) > (0,10) > (0,15) > (0,20) > (0,25) > (0,30) > (0,35) > (0,40) > (0,45) > (0,50) > (10 rows) And I think we all agree, that better index correlation leads to better performance. >> I think this is a *very* dubious idea. It introduces a low-level >> implementation dependency into our sort behavior The patch modifies the static function comparetup_index() in tuplesort.c. The comment above this function says /* * Routines specialized for IndexTuple case * * NOTE: actually, these are specialized for the btree case; [...] */ comparetup_index() compares two IndexTuples. The structure IndexTupleData consists basically of not much more than an ItemPointer, and the patch is not much more than adding a comparison of two ItemPointers. So how does the patch introduce a new low level implementation dependency? >Roger --- patch removed. Thanks. Could we agree on only removing the first five a half lines of the comment in the patch? Servus Manfred
Manfred Koizar <mkoi-pg@aon.at> writes:
> comparetup_index() compares two IndexTuples. The structure
> IndexTupleData consists basically of not much more than an ItemPointer,
> and the patch is not much more than adding a comparison of two
> ItemPointers. So how does the patch introduce a new low level
> implementation dependency?
Because it sorts on tuple position, which is certainly about as low
level as you can get. More to the point, though, no evidence has been
provided that this is a good idea.
regards, tom lane
On Mon, 01 Dec 2003 13:32:10 -0500, Tom Lane <tgl@sss.pgh.pa.us> wrote: >Manfred Koizar <mkoi-pg@aon.at> writes: >> comparetup_index() compares two IndexTuples. The structure >> IndexTupleData consists basically of not much more than an ItemPointer, >> and the patch is not much more than adding a comparison of two >> ItemPointers. So how does the patch introduce a new low level >> implementation dependency? > >Because it sorts on tuple position, which is certainly about as low >level as you can get. The patch affects only the sort during index creation. Mapping key values to tuple positions is the sole purpose of an index. The notion that an index should not care for tuple positions looks a bit strange to me. > More to the point, though, no evidence has been >provided that this is a good idea. The test script I posted with the patch shows that the patch produces more efficient b-tree indices when there are lots of duplicates. Servus Manfred
Where are we on this? It seems like a win to me. --------------------------------------------------------------------------- Manfred Koizar wrote: > On Mon, 01 Dec 2003 13:32:10 -0500, Tom Lane <tgl@sss.pgh.pa.us> wrote: > >Manfred Koizar <mkoi-pg@aon.at> writes: > >> comparetup_index() compares two IndexTuples. The structure > >> IndexTupleData consists basically of not much more than an ItemPointer, > >> and the patch is not much more than adding a comparison of two > >> ItemPointers. So how does the patch introduce a new low level > >> implementation dependency? > > > >Because it sorts on tuple position, which is certainly about as low > >level as you can get. > > The patch affects only the sort during index creation. Mapping key > values to tuple positions is the sole purpose of an index. The notion > that an index should not care for tuple positions looks a bit strange to > me. > > > More to the point, though, no evidence has been > >provided that this is a good idea. > > The test script I posted with the patch shows that the patch produces > more efficient b-tree indices when there are lots of duplicates. > > Servus > Manfred > > ---------------------------(end of broadcast)--------------------------- > TIP 4: Don't 'kill -9' the postmaster > -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
Here is more detail on the patch. --------------------------------------------------------------------------- Manfred Koizar wrote: > On Mon, 1 Dec 2003 00:02:54 -0500 (EST), Bruce Momjian > <pgman@candle.pha.pa.us> wrote: > >Tom Lane wrote: > >> Bruce Momjian <pgman@candle.pha.pa.us> writes: > >> >> And if it doesn't help index > >> >> creation speed, at least the resulting index has better correlation. > > ... which has been shown by the example in the original message: > > Result without patch: > > ctid > > ---------- > > (153,14) > > (306,23) > > (305,80) > > (152,91) > > (76,68) > > (38,34) > > (153,34) > > (305,50) > > (9,62) > > (305,40) > > (10 rows) > > > > Result with patch: > > ctid > > -------- > > (0,5) > > (0,10) > > (0,15) > > (0,20) > > (0,25) > > (0,30) > > (0,35) > > (0,40) > > (0,45) > > (0,50) > > (10 rows) > > And I think we all agree, that better index correlation leads to better > performance. > > >> I think this is a *very* dubious idea. It introduces a low-level > >> implementation dependency into our sort behavior > > The patch modifies the static function comparetup_index() in > tuplesort.c. > The comment above this function says > /* > * Routines specialized for IndexTuple case > * > * NOTE: actually, these are specialized for the btree case; [...] > */ > > comparetup_index() compares two IndexTuples. The structure > IndexTupleData consists basically of not much more than an ItemPointer, > and the patch is not much more than adding a comparison of two > ItemPointers. So how does the patch introduce a new low level > implementation dependency? > > >Roger --- patch removed. Thanks. > > Could we agree on only removing the first five a half lines of the > comment in the patch? > > Servus > Manfred > > ---------------------------(end of broadcast)--------------------------- > TIP 3: if posting/reading through Usenet, please send an appropriate > subscribe-nomail command to majordomo@postgresql.org so that your > message can get through to the mailing list cleanly > -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Where are we on this? It seems like a win to me.
I thought it was a bad idea, although I no longer remember the details.
regards, tom lane
Tom Lane wrote: > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > Where are we on this? It seems like a win to me. > > I thought it was a bad idea, although I no longer remember the details. If I remember correctly, you didn't like the index routines reading the tuple information, or something like that, but there was a performance benefit for duplicate keys, so I think we should re-investigate this. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> If I remember correctly, you didn't like the index routines reading the
> tuple information, or something like that, but there was a performance
> benefit for duplicate keys, so I think we should re-investigate this.
I don't see the actual patch either in the hackers or patches archives,
nor on your to-apply pages, making it a bit difficult to re-investigate.
Where was it posted anyway?
regards, tom lane
Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > If I remember correctly, you didn't like the index routines reading the
> > tuple information, or something like that, but there was a performance
> > benefit for duplicate keys, so I think we should re-investigate this.
>
> I don't see the actual patch either in the hackers or patches archives,
> nor on your to-apply pages, making it a bit difficult to re-investigate.
> Where was it posted anyway?
Found it:
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=200312010450.hB14ovH16330%40candle.pha.pa.us&rnum=8
Personally, because frequently accessed duplicates appear more forward
in the duplicate index, I think the sorting is only valuable when
creating a new index.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
Bruce Momjian <pgman@candle.pha.pa.us> writes: > Tom Lane wrote: >> Where was it posted anyway? > Found it: > http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=200312010450.hB14ovH16330%40candle.pha.pa.us&rnum=8 Thanks. The original patch is much older than I thought --- I was looking in the November/December part of the archives. > Personally, because frequently accessed duplicates appear more forward > in the duplicate index, I think the sorting is only valuable when > creating a new index. Yes, and that's what this does. Looking back, the original discussion got a little confused because the TODO item about "order duplicate index entries by tid" got brought into the mix. Actually this patch has nothing to do with that, because it only acts during btree creation not during index updates. On inspection I have no problem with the patch, only with the comments ;-) If you like I'll revise the comments and apply. regards, tom lane
Tom Lane wrote: > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > Tom Lane wrote: > >> Where was it posted anyway? > > > Found it: > > > http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=200312010450.hB14ovH16330%40candle.pha.pa.us&rnum=8 > > Thanks. The original patch is much older than I thought --- I was > looking in the November/December part of the archives. > > > Personally, because frequently accessed duplicates appear more forward > > in the duplicate index, I think the sorting is only valuable when > > creating a new index. > > Yes, and that's what this does. Looking back, the original discussion > got a little confused because the TODO item about "order duplicate index > entries by tid" got brought into the mix. Actually this patch has > nothing to do with that, because it only acts during btree creation not > during index updates. > > On inspection I have no problem with the patch, only with the comments ;-) > If you like I'll revise the comments and apply. Great. Seems harmless and he showed good performance with it. I agree the discussion got confused, and that is why I kept it in my mailbox to revisit. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073