From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Victor Yegorov <viy(at)pirmabanka(dot)lv> |
Cc: | pgsql-admin(at)postgresql(dot)org |
Subject: | Re: DB archiving |
Date: | 2003-03-17 15:53:23 |
Message-ID: | 6522.1047916403@sss.pgh.pa.us |
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Lists: | pgsql-admin |
Victor Yegorov <viy(at)pirmabanka(dot)lv> writes:
> One more thing. I still cannot find any info on HOW pg_dump locks data it
> is going to backup.
It doesn't. Well, it does take a reader's lock (AccessShareLock) on
each table it intends to back up, but that's essentially just preventing
the table from being dropped completely. The individual data rows need
not be locked. pg_dump does the whole dump as a single transaction, so
it can rely on MVCC semantics to give it a consistent picture of the
data in every table. Basically, it doesn't "see" changes that commit
after its transaction starts. See the discussion of MVCC.
regards, tom lane
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