Re: Curious about exclusive table locks

"Uwe C. Schroeder" <uwe(at)oss4u(dot)com> writes:
> Tom: What did you mean by "snapshot has been set" ?

Read the MVCC documentation. Also it'd be worth your while to read the
slides from my 2002 O'Reilly talk:
http://conferences.oreillynet.com/cs/os2002/view/e_sess/2681
I've been meaning to get those slides put onto the Postgres web site,
but it's never gotten done ...

The slides don't really go into the issues for writing functions,
but the critical point is that the snapshot does not change while
a function runs; it's set when the interactive command that invokes
the function begins. (There has been some discussion about whether
this is a bug or not, but that's how it works in all extant releases.)

regards, tom lane