Re: GiST seems to drop left-branch leaf tuples - Mailing list pgsql-hackers

On Nov 23, 2010, at 1:37 PM, Yeb Havinga wrote:
>>>> j = 0;
>>>> for (i = FirstOffsetNumber; i < maxoff; i = OffsetNumberNext(i)) {
>>>>   FPrint* v = deserialize_fprint(entv[i].key);
>>>
>>> Isn't this off by one?  Offset numbers are 1-based, so the maxoff
>>> computation is wrong.
> The first for loop of all others compare with i <= maxoff instead of i < maxoff.

You are right: I am missing the last one, there.  (During a memory-debugging phase entv[entryvec-n - 1] was always
invalid,probably as a memory overwrite error but I fixed that later and never changed it back.) 

On the other hand, there are two problems:

1. the maximum size on a GiST page is 4240 bytes, so I cannot add a full-size Datum using this kind of hash-key setup
(thebase Datum size is 4230 bytes on a 64-bit machine).  The example test cases I used were smaller in order to get
aroundthat issue: they are 2326 bytes base size.   

2. Even after fixing the Picksplit() loop, the dropped-leaf problem still manifests itself:

postgres=# set enable_seqscan=false;
SET
postgres=# set enable_indexscan=true;
SET
postgres=# create table fps2 (id serial, soid character(24) not null, fingerprint fprint not null);
NOTICE:  CREATE TABLE will create implicit sequence "fps2_id_seq" for serial column "fps2.id"
CREATE TABLE
postgres=# create index fps2_fingerprint_ix on fps2 using gist (fingerprint fprint_gist_ops);
CREATE INDEX
postgres=# \i xaa
psql:xaa:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
INSERT 0 1
postgres=# \i xab
psql:xab:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
INSERT 0 1
postgres=# \i xac
psql:xac:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
INSERT 0 1
postgres=# \i xad
psql:xad:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
INSERT 0 1
postgres=# select gist_stat('fps2_fingerprint_ix');              gist_stat
---------------------------------------Number of levels:          1         +Number of pages:           1
+Numberof leaf pages:      1         +Number of tuples:          4         +Number of invalid tuples:  0
+Numberof leaf tuples:     4         +Total size of tuples:      5628 bytes+Total size of leaf tuples: 5628 bytes+Total
sizeof index:       8192 bytes+ 

postgres=# \i xae
psql:xae:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
INSERT 0 1
postgres=# select gist_stat('fps2_fingerprint_ix');              gist_stat
---------------------------------------Number of levels:          1         +Number of pages:           1
+Numberof leaf pages:      1         +Number of tuples:          5         +Number of invalid tuples:  0
+Numberof leaf tuples:     5         +Total size of tuples:      7032 bytes+Total size of leaf tuples: 7032 bytes+Total
sizeof index:       8192 bytes+ 

postgres=# \i xaf
psql:xaf:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
psql:xaf:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaf:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaf:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaf:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaf:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaf:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaf:1: NOTICE:  [pgfprint.c:fprint_picksplit:659] entered picksplit
psql:xaf:1: NOTICE:  [pgfprint.c:fprint_picksplit:838] split: 3 left, 2 right
psql:xaf:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
psql:xaf:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
INSERT 0 1
postgres=# select gist_stat('fps2_fingerprint_ix');              gist_stat
----------------------------------------Number of levels:          2          +Number of pages:           3
+Numberof leaf pages:      2          +Number of tuples:          7          +Number of invalid tuples:  0
+Numberof leaf tuples:     5          +Total size of tuples:      9864 bytes +Total size of leaf tuples: 7044 bytes
+Totalsize of index:       24576 bytes+ 

postgres=# select id, soid from fps2;id |           soid
----+-------------------------- 1 | 4c65a39d4d9bca2c33000082 2 | 4c65a39d4d9bca2c3300008a 3 | 4c65a39d4d9bca2c33000090
4| 4c65a39d4d9bca2c33000099 5 | 4c65a39d4d9bca2c330000a5 6 | 4c65a39d4d9bca2c330000a8 

postgres=# select f1.id, f2.id, fprint_cmp(f1.fingerprint, f2.fingerprint) from fps2 f1 join fps2 f2 on
f1.fingerprint=f2.fingerprint;id| id |    fprint_cmp     
----+----+------------------ 1 |  1 | 1.00031467691569 2 |  2 | 1.00031467691569 4 |  4 | 1.00031467691569 5 |  5 |
1.000314676915696 |  6 | 1.00031467691569 
So GiST does not include a tuple for row 3; one of the old tuples.

After inserting a few more rows to trigger another Picksplit():

postgres=# \i xag
psql:xag:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
psql:xag:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xag:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xag:1: NOTICE:  [pgfprint.c:fprint_penalty:913] entered penalty
psql:xag:1: NOTICE:  [pgfprint.c:fprint_penalty:935] penalty: 703.4312133789062500
psql:xag:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xag:1: NOTICE:  [pgfprint.c:fprint_penalty:913] entered penalty
psql:xag:1: NOTICE:  [pgfprint.c:fprint_penalty:935] penalty: 832.1127319335937500
psql:xag:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xag:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xag:1: NOTICE:  [pgfprint.c:fprint_union:453] entered union
psql:xag:1: NOTICE:  [pgfprint.c:fprint_same:951] entered same
psql:xag:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
psql:xag:1: NOTICE:  [pgfprint.c:fprint_compress:384] returning non-leafkey entry raw
INSERT 0 1
postgres=# \i xah
psql:xah:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
psql:xah:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xah:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xah:1: NOTICE:  [pgfprint.c:fprint_penalty:913] entered penalty
psql:xah:1: NOTICE:  [pgfprint.c:fprint_penalty:935] penalty: 880.7246093750000000
psql:xah:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xah:1: NOTICE:  [pgfprint.c:fprint_penalty:913] entered penalty
psql:xah:1: NOTICE:  [pgfprint.c:fprint_penalty:935] penalty: 903.4860839843750000
psql:xah:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xah:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xah:1: NOTICE:  [pgfprint.c:fprint_union:453] entered union
psql:xah:1: NOTICE:  [pgfprint.c:fprint_same:951] entered same
psql:xah:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
psql:xah:1: NOTICE:  [pgfprint.c:fprint_compress:384] returning non-leafkey entry raw
INSERT 0 1
postgres=# \i xai
psql:xai:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
psql:xai:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xai:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xai:1: NOTICE:  [pgfprint.c:fprint_penalty:913] entered penalty
psql:xai:1: NOTICE:  [pgfprint.c:fprint_penalty:935] penalty: 904.7127075195312500
psql:xai:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xai:1: NOTICE:  [pgfprint.c:fprint_penalty:913] entered penalty
psql:xai:1: NOTICE:  [pgfprint.c:fprint_penalty:935] penalty: 907.4243164062500000
psql:xai:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xai:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xai:1: NOTICE:  [pgfprint.c:fprint_union:453] entered union
psql:xai:1: NOTICE:  [pgfprint.c:fprint_same:951] entered same
psql:xai:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
psql:xai:1: NOTICE:  [pgfprint.c:fprint_compress:384] returning non-leafkey entry raw
INSERT 0 1
postgres=# \i xaj
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_penalty:913] entered penalty
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_penalty:935] penalty: 910.3089599609375000
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_penalty:913] entered penalty
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_penalty:935] penalty: 906.1793212890625000
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_picksplit:659] entered picksplit
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_picksplit:838] split: 2 left, 3 right
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_compress:384] returning non-leafkey entry raw
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_compress:384] returning non-leafkey entry raw
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_decompress:419] entered decompress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_union:453] entered union
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_compress:379] entered compress
psql:xaj:1: NOTICE:  [pgfprint.c:fprint_compress:384] returning non-leafkey entry raw
INSERT 0 1
postgres=# select id, soid from fps2;id |           soid
----+-------------------------- 1 | 4c65a39d4d9bca2c33000082 2 | 4c65a39d4d9bca2c3300008a 3 | 4c65a39d4d9bca2c33000090
4| 4c65a39d4d9bca2c33000099 5 | 4c65a39d4d9bca2c330000a5 6 | 4c65a39d4d9bca2c330000a8 7 | 4c65a39d4d9bca2c330000b0 8 |
4c65a39d4d9bca2c330000be9 | 4c65a39d4d9bca2c330000c810 | 4c65a39d4d9bca2c330000d3 
(10 rows)

postgres=# select f1.id, f2.id, fprint_cmp(f1.fingerprint, f2.fingerprint) from fps2 f1 join fps2 f2 on
f1.fingerprint=f2.fingerprint;id| id |    fprint_cmp     
----+----+------------------ 1 |  1 | 1.00031467691569 4 |  4 | 1.00031467691569 5 |  5 | 1.00031467691569 6 |  6 |
1.000314676915697 |  7 | 1.00031467691569 8 |  8 | 1.00031467691569 9 |  9 | 1.0003146769156910 | 10 | 1.00031467691569 
(8 rows)

Index tuples for rows 3 and 2 have been dropped.