_bt_check_unique checks every row in table when doing update??

Hi, I'm running 7.2.1 on a sparc/solaris box. I get performance problems
when doing updates in one of my tables (inserts are faster), so I tried
to run it with profiling enabled.

With reservations for my non-existent knowledge of the code, the results
do look like the bad performance is because of some bug.

When doing ~1000 inserts into the testdata table, gprof says
this about _bt_check_unique which looks reasonable:

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

0.00 0.01 1002/1002 _bt_doinsert [86]
[264] 0.1 0.00 0.01 1002 _bt_check_unique [264]
0.00 0.01 1006/1006 _bt_isequal [271]
0.00 0.00 1002/67941 _bt_binsrch <cycle 1> [4417]
0.00 0.00 6/429 heap_fetch [331]
0.00 0.00 2/857310 ReleaseBuffer [50]

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

But when doing ~1000 updates (i.e. setting val0 and val1 with
a where on an existing key0/key1/key2 triplet), I get this which
seems very strange to me:

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

0.10 6.43 1002/1002 _bt_doinsert [21]
[22] 17.3 0.10 6.43 1002 _bt_check_unique [22]
0.40 3.21 505436/505436 _bt_isequal [26]
0.57 2.22 500509/1000450 heap_fetch [23]
0.00 0.01 4926/27777 _bt_getbuf [157]
0.00 0.00 4926/25330 _bt_relbuf [262]
0.00 0.00 1002/2213707 _bt_binsrch <cycle 1> [4425]
0.00 0.00 1001/1878622 ReleaseBuffer [41]

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

The schema is as follows:

mats=# \d testdata
Table "testdata"
Column | Type | Modifiers
--------+-----------------------+-----------
key0 | character varying(32) | not null
key1 | character varying(32) | not null
key2 | character varying(32) | not null
val0 | character varying(64) | not null
val1 | text | not null
Indexes: testdataval0index
Unique keys: testdataindex

mats=# \d testdataindex
Index "testdataindex"
Column | Type
--------+-----------------------
key0 | character varying(32)
key1 | character varying(32)
key2 | character varying(32)
unique btree

mats=# \d testdataval0index
Index "testdataval0index"
Column | Type
--------+-----------------------
val0 | character varying(64)
btree

mats=# select count(*) from testdata;
count
--------
435614
(1 row)

Note that he number of calls to _bt_isequal is very close to the
number of rows in the table plus the number of dead rows.

Vacuum analyze and/or recreating the unique index makes no
difference as far as I can tell.

(The fact that _bt_check_unique is called at all when
doing an update seems strange by itself, but shouldn't be
a problem if it was just done as efficiently as when doing
an insert.)

_
Mats Lofkvist
mal(at)algonet(dot)se