Hi
I'll try to vaccum first before I start the delete to see if it change something.I rerun the example with the debug info turned on in postgresl. As you can see all dependent tables (that as foreign key on table IC) are emptied before the DELETE FROM IC statement is issued. For what I understand the performance problem seem to came from those selects that point back to IC ( LOG: statement: SELECT 1 FROM ONLY "public"."ic" x WHERE "icnum" = $1 FOR UPDATE OF x). There are 6 of them. I don't know where they are comming from.
I think they come from the FK checking code. Try to run a VACUUM on the
IC table just before you delete from the other tables; that should make
the checking almost instantaneous (assuming the vacuuming actually
empties the table, which would depend on other transactions).
There is probably a good reason why but I don't understant why in a foreign key check it need to check the date it points to.
You delete a row from table IC and do a check for integrity on tables that have foreign keys on IC (make sense). But why checking back IC? I'm pretty sure there is a good reason but it seems to have a big performance impact... In this case. It means it's not really feasable to empty the content of a schema. The table has only 10k .. with a huge table it's not feasible just because the checks on itselft!
Is someone can explain why there is this extra check? Is that can be fixed or improved?
Thanks for your help
/David
LOG: duration: 144.000 ms
LOG: statement: DELETE FROM YN
LOG: duration: 30.000 ms
LOG: statement: DELETE FROM YO
LOG: statement: SELECT 1 FROM ONLY "public"."yo" x WHERE "yotype" = $1 AND "yonum" = $2 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."yn" x WHERE "ynyotype" = $1 AND "ynyonum" = $2 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."yo" x WHERE "yotype" = $1 AND "yonum" = $2 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."yr" x WHERE "yryotype" = $1 AND "yryonum" = $2 FOR UPDATE OF x
LOG: duration: 83.000 ms
LOG: connection received: host=127.0.0.1 port=2196
LOG: connection authorized: user=admin database=webCatalog
LOG: statement: set datestyle to 'ISO'; select version(), case when pg_encoding_to_char(1) = 'SQL_ASCII' then 'UNKNOWN' else getdatabaseencoding() end;
LOG: duration: 2.000 ms
LOG: statement: set client_encoding = 'UNICODE'
LOG: duration: 0.000 ms
LOG: statement: DELETE FROM IY
LOG: duration: 71.000 ms
LOG: statement: DELETE FROM IA
LOG: duration: 17.000 ms
LOG: statement: DELETE FROM IQ
LOG: duration: 384.000 ms
LOG: statement: DELETE FROM IC
LOG: statement: SELECT 1 FROM ONLY "public"."ic" x WHERE "icnum" = $1 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."iq" x WHERE "iqicnum" = $1 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."ic" x WHERE "icnum" = $1 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."ia" x WHERE "iaicnum" = $1 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."ic" x WHERE "icnum" = $1 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."iy" x WHERE "iyicnumo" = $1 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."ic" x WHERE "icnum" = $1 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."iy" x WHERE "iyicnumr" = $1 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."ic" x WHERE "icnum" = $1 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."il" x WHERE "ilicnum" = $1 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."ic" x WHERE "icnum" = $1 FOR UPDATE OF x
LOG: statement: SELECT 1 FROM ONLY "public"."bd" x WHERE "bdicnum" = $1 FOR UPDATE OF x
LOG: duration: 656807.000 msMichael Fuhr wrote:
It would be better to be able to use TRUNCATE to do this, but in 8.0 you can't if the tables have FKs. 8.1 is better on that regard ...
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