Hey,
I've gone and increased shared memory and now the deletes
seem to be really fast. I guess it had to do with postgresql not being
able to keep all the tables/indexes in memory and having to read/write
everything from the disk.
I'll look at the utils anyway and see if there really is
unindexed foreign keys, but from first glance it looks like they're all
indexed.
Thanks for your suggestion.
Steve.
From: Reece Hart [mailto:reece@xxxxxxxxx]
Sent: Thursday, November 02, 2006 2:53 PM
To: Tom Lane
Cc: Schwenker, Stephen; Michael Fuhr; pgsql-general@xxxxxxxxxxxxxx
Subject: Re: [GENERAL] DELETE performance issues
Are you absolutely sure about that last? Unindexed foreign key
references are the explanation nine times out of ten when someone
complains about deletes being slow.
This was certainly the major cause when I had slow deletes. (The other problem was chaining of cascading deletes.) In order to help correct such problems, I wrote some views to identify unindexed, cascading foreign keys. An example:
rkh@csb-dev=> select * from pgutils.foreign_keys_missing_indexes ; fk_namespace | fk_relation | fk_column | fk_indexed | pk_namespace | pk_relation | pk_column | pk_indexed | ud ... --------------+--------------+---------------------+------------+--------------+-------------+-------------+------------+--- ... gong | node | alias_id | f | gong | alias | alias_id | t | cn ... taxonomy | node | division_id | f | taxonomy | division | division_id | t | cc ... gong | alias | go_id | f | gong | node | go_id | t | cc ...etc...
ud is an abbreviation for update and delete constraint type (cascade, set null, restrict, etc).
In this view, "indexed" means that the column is the first or only column in some index, i.e., pg_index.indkey[0] = pg_attribute.attnum. I suppose that one might want to distinguish the indexing cases more precisely as unindexed, sole-column index, first col of mult-col index, second col of multi-col index, etc, but I didn't do so. The views were originally written for 7.4 and I don't know what's appropriate for current multicolumn index behavior.
The code is in http://harts.net/reece/pgutils/ .
-Reece
-- Reece Hart, http://harts.net/reece/, GPG:0x25EC91A0 |
