Re: pg_relation_size locking

Tom Lane wrote:
> Andreas Pflug <pgadmin@pse-consulting.de> writes:
> 
>>Tom Lane wrote:
>>
>>>Nonsense.
> 
> 
>>Ahem.
> 
> 
>>I'm running Slony against a big replication set. While slon runs COPY 
>>foo(colnamelist) FROM STDIN, I can't execute pg_relation_size(foo_oid). 
>>pg_locks will show that the AccessShareLock on foo is not granted.
> 
> 
> That's only possible if Slony is taking AccessExclusive lock; if so,
> your gripe is properly directed to the Slony folks, not to
> pg_relation_size which is acting as a good database citizen should.

More precisely, it executes TRUNCATE;COPY at the same time; there might 
be additional locks to prevent using the table. Still, I see no reason 
why pg_relation_size shouldn't continue to use SearchSysCache as id did 
for years now. There's no sense in using locking mechanisms on table foo 
while reading file system data; pg_class is sufficient to locate the 
table's files.

Regards,
Andreas