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Re: Modifying TOAST thresholds - Mailing list pgsql-hackers

From Bruce Momjian
Subject Re: Modifying TOAST thresholds
Date
Msg-id 200704050204.l3524Rq20622@momjian.us
Whole thread Raw
In response to Re: Modifying TOAST thresholds  (Chris Browne <cbbrowne@acm.org>)
List pgsql-hackers
Tree view 
Patch rejected, since we have decided we need to have this as part of
CREATE/ALTER table, rather than a GUC.

---------------------------------------------------------------------------

Chris Browne wrote:
> tgl@sss.pgh.pa.us (Tom Lane) writes:
> > "Simon Riggs" <simon@2ndquadrant.com> writes:
> >> Well it certainly seems worth separating them. It does seem possible
> >> that recursive toasting effected some of the earlier results we looked
> >> at.
> >
> >> Would you like me to do this, or will you?
> >
> > I'm willing to do the code changes to separate TOAST_THRESHOLD from
> > the toast chunk size, but I do not have the time or facilities to do
> > any performance testing for different parameter choices.  Anyone want
> > to work on that?
> >
> >> I'd like to get some mechanism for reducing WAL volume into 8.3, whether
> >> its configurable toast or WAL reduction for UPDATEs. If for no other
> >> reason than making backup and availability solutions more manageable.
> >
> > I think the WAL-reduction proposal needs more time and thought than is
> > feasible before 8.3.  OTOH, tuning the TOAST parameters seems like
> > something we understand well enough already, we just need to put some
> > cycles into testing different alternatives.  I would have no objection
> > to someone working on that during April and delivering a final patch
> > sometime before beta.
> 
> Here's a "drafty" patch that *tries* to do this using a GUC variable;
> it passes some interactive testing.  It probably needs an
> assign_hook() function to do further validation (probably to make sure
> that sizes are rightly aligned on both 32 and 64 bit platforms); feel
> free to consider me incompetent at this stage at generating such...
> 
> I would *very* much like to see something of this sort in 8.3; that
> would be of definite value to some of our applications which store
> data that is a bit too small to meet the present
> TOAST_TUPLE_THRESHOLD.  (E.g. - it's worth noting that common
> SOAP-like XML requests are in the 700-1000 byte range; such values are
> generally nicely compressible and are often not likely to be used in
> summary-oriented queries on mainline tables...)
> 
> I don't think I can come up with a performance "test suite" this week,
> and will be unavailable from April 6-14th; if others were to find this
> valuable, and volunteer to set up some sort of test in the interim,
> that would be super.  Absent that, I should be able to do some work on
> this in the latter half of April.
> 
> set toast_default_threshold TO 128;
> create table sample (id serial primary key, txt text);
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> create table sample (id serial primary key, txt text);
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> set toast_default_threshold TO 250;
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> insert into sample (txt) values
('12347890347902317849018732417094739027847891230978041237890341278904123789012347980123479081234789041378901234789041237980123478901423789014237980123478901342789014237890142378901423');
> 
> test@[local]:5883=# vacuum verbose sample;
> INFO:  vacuuming "public.sample"
> INFO:  index "sample_pkey" now contains 52 row versions in 2 pages
> DETAIL:  0 index row versions were removed.
> 0 index pages have been deleted, 0 are currently reusable.
> CPU 0.00s/0.00u sec elapsed 0.00 sec.
> INFO:  "sample": found 0 removable, 52 nonremovable row versions in 1 pages
> DETAIL:  0 dead row versions cannot be removed yet.
> There were 0 unused item pointers.
> 1 pages contain useful free space.
> 0 pages are entirely empty.
> CPU 0.00s/0.00u sec elapsed 0.00 sec.
> INFO:  vacuuming "pg_toast.pg_toast_16387"
> INFO:  index "pg_toast_16387_index" now contains 25 row versions in 2 pages
> DETAIL:  0 index row versions were removed.
> 0 index pages have been deleted, 0 are currently reusable.
> CPU 0.00s/0.00u sec elapsed 0.00 sec.
> INFO:  "pg_toast_16387": found 0 removable, 25 nonremovable row versions in 1 pages
> DETAIL:  0 dead row versions cannot be removed yet.
> There were 0 unused item pointers.
> 1 pages contain useful free space.
> 0 pages are entirely empty.
> CPU 0.00s/0.00u sec elapsed 0.00 sec.
> VACUUM
> ------------------------------------
> ? Makefile.global
> ? backend/postgres
> ? backend/catalog/postgres.bki
> ? backend/catalog/postgres.description
> ? backend/catalog/postgres.shdescription
> ? backend/utils/mb/conversion_procs/conversion_create.sql
> ? backend/utils/mb/conversion_procs/ascii_and_mic/libascii_and_mic.so.0.0
> ? backend/utils/mb/conversion_procs/cyrillic_and_mic/libcyrillic_and_mic.so.0.0
> ? backend/utils/mb/conversion_procs/euc_cn_and_mic/libeuc_cn_and_mic.so.0.0
> ? backend/utils/mb/conversion_procs/euc_jis_2004_and_shift_jis_2004/libeuc_jis_2004_and_shift_jis_2004.so.0.0
> ? backend/utils/mb/conversion_procs/euc_jp_and_sjis/libeuc_jp_and_sjis.so.0.0
> ? backend/utils/mb/conversion_procs/euc_kr_and_mic/libeuc_kr_and_mic.so.0.0
> ? backend/utils/mb/conversion_procs/euc_tw_and_big5/libeuc_tw_and_big5.so.0.0
> ? backend/utils/mb/conversion_procs/latin2_and_win1250/liblatin2_and_win1250.so.0.0
> ? backend/utils/mb/conversion_procs/latin_and_mic/liblatin_and_mic.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_ascii/libutf8_and_ascii.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_big5/libutf8_and_big5.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_cyrillic/libutf8_and_cyrillic.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_euc_cn/libutf8_and_euc_cn.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_euc_jis_2004/libutf8_and_euc_jis_2004.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_euc_jp/libutf8_and_euc_jp.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_euc_kr/libutf8_and_euc_kr.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_euc_tw/libutf8_and_euc_tw.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_gb18030/libutf8_and_gb18030.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_gbk/libutf8_and_gbk.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_iso8859/libutf8_and_iso8859.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_iso8859_1/libutf8_and_iso8859_1.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_johab/libutf8_and_johab.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_shift_jis_2004/libutf8_and_shift_jis_2004.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_sjis/libutf8_and_sjis.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_uhc/libutf8_and_uhc.so.0.0
> ? backend/utils/mb/conversion_procs/utf8_and_win/libutf8_and_win.so.0.0
> ? bin/initdb/initdb
> ? bin/ipcclean/ipcclean
> ? bin/pg_config/pg_config
> ? bin/pg_controldata/pg_controldata
> ? bin/pg_ctl/pg_ctl
> ? bin/pg_dump/pg_dump
> ? bin/pg_dump/pg_dumpall
> ? bin/pg_dump/pg_restore
> ? bin/pg_resetxlog/pg_resetxlog
> ? bin/psql/psql
> ? bin/scripts/clusterdb
> ? bin/scripts/createdb
> ? bin/scripts/createlang
> ? bin/scripts/createuser
> ? bin/scripts/dropdb
> ? bin/scripts/droplang
> ? bin/scripts/dropuser
> ? bin/scripts/reindexdb
> ? bin/scripts/vacuumdb
> ? include/pg_config.h
> ? include/stamp-h
> ? interfaces/ecpg/compatlib/libecpg_compat.so.2.2
> ? interfaces/ecpg/compatlib/libecpg_compat.so.2.3
> ? interfaces/ecpg/ecpglib/libecpg.so.5.2
> ? interfaces/ecpg/ecpglib/libecpg.so.5.3
> ? interfaces/ecpg/include/ecpg_config.h
> ? interfaces/ecpg/pgtypeslib/libpgtypes.so.2.2
> ? interfaces/ecpg/pgtypeslib/libpgtypes.so.2.3
> ? interfaces/ecpg/preproc/ecpg
> ? interfaces/ecpg/test/sql/dyntest2
> ? interfaces/ecpg/test/sql/dyntest2.c
> ? interfaces/libpq/exports.list
> ? interfaces/libpq/libpq.so.5.0
> ? interfaces/libpq/libpq.so.5.1
> ? pl/plpgsql/src/libplpgsql.so.1.0
> ? port/pg_config_paths.h
> ? test/regress/libregress.so.0.0
> ? test/regress/log
> ? test/regress/pg_regress
> ? test/regress/results
> ? test/regress/testtablespace
> ? test/regress/tmp_check
> ? test/regress/expected/constraints.out
> ? test/regress/expected/copy.out
> ? test/regress/expected/create_function_1.out
> ? test/regress/expected/create_function_2.out
> ? test/regress/expected/largeobject.out
> ? test/regress/expected/largeobject_1.out
> ? test/regress/expected/misc.out
> ? test/regress/expected/tablespace.out
> ? test/regress/sql/constraints.sql
> ? test/regress/sql/copy.sql
> ? test/regress/sql/create_function_1.sql
> ? test/regress/sql/create_function_2.sql
> ? test/regress/sql/largeobject.sql
> ? test/regress/sql/misc.sql
> ? test/regress/sql/tablespace.sql
> ? timezone/zic
> Index: backend/access/heap/heapam.c
> ===================================================================
> RCS file: /projects/cvsroot/pgsql/src/backend/access/heap/heapam.c,v
> retrieving revision 1.230
> diff -c -u -r1.230 heapam.c
> --- backend/access/heap/heapam.c    29 Mar 2007 00:15:37 -0000    1.230
> +++ backend/access/heap/heapam.c    2 Apr 2007 22:41:05 -0000
> @@ -57,6 +57,7 @@
>  #include "utils/relcache.h"
>  #include "utils/syscache.h"
>  
> +extern int toast_default_threshold;
>  
>  static XLogRecPtr log_heap_update(Relation reln, Buffer oldbuf,
>             ItemPointerData from, Buffer newbuf, HeapTuple newtup, bool move);
> Index: backend/access/heap/tuptoaster.c
> ===================================================================
> RCS file: /projects/cvsroot/pgsql/src/backend/access/heap/tuptoaster.c,v
> retrieving revision 1.72
> diff -c -u -r1.72 tuptoaster.c
> --- backend/access/heap/tuptoaster.c    29 Mar 2007 00:15:37 -0000    1.72
> +++ backend/access/heap/tuptoaster.c    2 Apr 2007 22:41:05 -0000
> @@ -42,6 +42,7 @@
>  
>  #undef TOAST_DEBUG
>  
> +extern int toast_default_threshold;
>  static void toast_delete_datum(Relation rel, Datum value);
>  static Datum toast_save_datum(Relation rel, Datum value,
>                                bool use_wal, bool use_fsm);
> Index: backend/catalog/toasting.c
> ===================================================================
> RCS file: /projects/cvsroot/pgsql/src/backend/catalog/toasting.c,v
> retrieving revision 1.5
> diff -c -u -r1.5 toasting.c
> --- backend/catalog/toasting.c    9 Jan 2007 02:14:11 -0000    1.5
> +++ backend/catalog/toasting.c    2 Apr 2007 22:41:05 -0000
> @@ -33,7 +33,7 @@
>  
>  static bool create_toast_table(Relation rel, Oid toastOid, Oid toastIndexOid);
>  static bool needs_toast_table(Relation rel);
> -
> +extern int toast_default_threshold;
>  
>  /*
>   * AlterTableCreateToastTable
> Index: backend/utils/misc/guc.c
> ===================================================================
> RCS file: /projects/cvsroot/pgsql/src/backend/utils/misc/guc.c,v
> retrieving revision 1.383
> diff -c -u -r1.383 guc.c
> --- backend/utils/misc/guc.c    19 Mar 2007 23:38:30 -0000    1.383
> +++ backend/utils/misc/guc.c    2 Apr 2007 22:41:06 -0000
> @@ -195,6 +195,7 @@
>  int            client_min_messages = NOTICE;
>  int            log_min_duration_statement = -1;
>  int            log_temp_files = -1;
> +int toast_default_threshold = MAXALIGN_DOWN((BLCKSZ - MAXALIGN(sizeof(PageHeaderData) + 3 * sizeof(ItemIdData))) /
4);
>  
>  int            num_temp_buffers = 1000;
>  
> @@ -1695,6 +1696,17 @@
>          -1, -1, INT_MAX, NULL, NULL
>      },
>  
> +    {
> +        {"toast_default_threshold", PGC_SUSET, CUSTOM_OPTIONS,
> +            gettext_noop("Tuples larger than this size will be considered for TOASTing"),
> +         gettext_noop("Default is ~ BLKSIZE / 4"),
> +         NULL
> +        },
> +        &toast_default_threshold,
> +        MAXALIGN_DOWN((BLCKSZ - MAXALIGN(sizeof(PageHeaderData) + 3 * sizeof(ItemIdData))) / 16), 
> +        128, BLCKSZ - MAXALIGN(sizeof(PageHeaderData) + 3 * sizeof(ItemIdData)), NULL, NULL
> +    },
> +
>      /* End-of-list marker */
>      {
>          {NULL, 0, 0, NULL, NULL}, NULL, 0, 0, 0, NULL, NULL
> Index: include/access/tuptoaster.h
> ===================================================================
> RCS file: /projects/cvsroot/pgsql/src/include/access/tuptoaster.h,v
> retrieving revision 1.33
> diff -c -u -r1.33 tuptoaster.h
> --- include/access/tuptoaster.h    29 Mar 2007 00:15:39 -0000    1.33
> +++ include/access/tuptoaster.h    2 Apr 2007 22:41:06 -0000
> @@ -38,12 +38,17 @@
>   * Note: sizeof(PageHeaderData) includes the first ItemId, but we have
>   * to allow for 3 more, if we want to fit 4 tuples on a page.
>   */
> -#define TOAST_TUPLE_THRESHOLD    \
> -    MAXALIGN_DOWN((BLCKSZ - \
> -                   MAXALIGN(sizeof(PageHeaderData) + 3 * sizeof(ItemIdData))) \
> -                  / 4)
>  
> -#define TOAST_TUPLE_TARGET        TOAST_TUPLE_THRESHOLD
> +/* #define TOAST_TUPLE_THRESHOLD    \ */
> +/*     MAXALIGN_DOWN((BLCKSZ - \ */
> +/*                    MAXALIGN(sizeof(PageHeaderData) + 3 * sizeof(ItemIdData))) \ */
> +/*                   / TOAST_DENOMINATOR) */
> +
> +/* #define TOAST_TUPLE_TARGET        TOAST_TUPLE_THRESHOLD */
> +
> +#define TOAST_TUPLE_THRESHOLD toast_default_threshold
> +
> +#define TOAST_TUPLE_TARGET        toast_default_threshold
>  
>  /*
>   * If an index value is larger than TOAST_INDEX_TARGET, we will try to
> @@ -65,11 +70,13 @@
>   * NB: you cannot change this value without forcing initdb, at least not
>   * if your DB contains any multi-chunk toasted values.
>   */
> -#define TOAST_MAX_CHUNK_SIZE    (TOAST_TUPLE_THRESHOLD -            \
> +#define TOAST_MAX_CHUNK_SIZE    ((MAXALIGN_DOWN((BLCKSZ -        \
> +                    MAXALIGN(sizeof(PageHeaderData) + 3 * sizeof(ItemIdData))) \
> +                           / 4)) -            \
>                  MAXALIGN(offsetof(HeapTupleHeaderData, t_bits)) -    \
>                  sizeof(Oid) -                                        \
>                  sizeof(int32) -                                        \
> -                VARHDRSZ)
> +                 VARHDRSZ)
>  
>  
>  /* ----------
> 
> -- 
> output = ("cbbrowne" "@" "linuxdatabases.info")
> http://cbbrowne.com/info/linuxxian.html
> When a man talks dirty to a woman, its sexual harassment. When a woman
> talks dirty to a man, it's 3.95 per minute.
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend

--  Bruce Momjian  <bruce@momjian.us>          http://momjian.us EnterpriseDB
http://www.enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +

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