I'm preparing for an upgrade from PostgreSQL 7.4.5 to 8.1.3, and I
noticed a potential performance issue.
I have two servers, a dual proc Dell with raid 5 running PostgreSQL
7.4, and a quad proc Dell with a storage array running PostgreSQL
8.1. Both servers have identical postgresql.conf settings and were
restored from the same 7.4 backup. Almost everything is faster on the
8.1 server (mostly due to hardware), except one thing...deletes from
tables with many foreign keys pointing to them.
I have table A with around 100,000 rows, that has foreign keys from
about 50 other tables pointing to it. Some of these other tables
(table B, for example) have around 10 million rows.
On the 7.4 server, I can delete a single row from a table A in well
under a second (as expected). On the 8.1 server, it takes over a
minute to delete. I tried all the usual stuff, recreating indexes,
vacuum analyzing, explain analyze. Everything is identical between
the systems. If I hit ctrl-c while the slow delete was running on
8.1, I repeatedly got the following message...
db=# delete from "A" where "ID" in ('6');
Cancel request sent
ERROR: canceling statement due to user request
CONTEXT: SQL statement "SELECT 1 FROM ONLY "public"."B" x WHERE
"A_ID" = $1 FOR SHARE OF x"
It looks to me like the "SELECT ... FOR SHARE" functionality in 8.1
is the culprit. Has anyone else run into this issue?
Will Reese -- http://blog.rezra.com
pgsql-performance by date
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