| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera Munoz <alvherre(at)dcc(dot)uchile(dot)cl> |
| Cc: | Haroldo Stenger <haroldo(dot)stenger(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Does psql use nested transactions? |
| Date: | 2004-08-17 21:10:45 |
| Message-ID: | 10131.1092777045@sss.pgh.pa.us |
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Alvaro Herrera Munoz <alvherre(at)dcc(dot)uchile(dot)cl> writes:
> Establishing a savepoint is a non-trivial operation (cost-wise). Several
> internal server structures have to be prepared for it.
Check
> It's way cheaper than normal transaction start and commit,
Is it? You have the same amount of work to do (sooner or later) in
terms of updating pg_clog, plus extra work to update pg_subtrans.
And in the abort case it can be worse than aborting a full xact, because
we have to do retail rather than wholesale release of locks, buffers, etc.
I have not had an opportunity to benchmark it but I fear a savepoint may
cost near as much as a full xact in practice.
regards, tom lane
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