On Apr 22, 2008, at 8:35 AM, Alvaro Herrera wrote:
Roberts, Jon wrote:
-With autovacuum, does it skip these rows still being referenced
in a transaction or does it wait?
It skips them, the idea being that a future vacuum will remove them.
Awesome. In a large data warehouse, the snapshot too old error is
very
annoying and I'm glad PostgreSQL is superior to Oracle in this
regard.
:)
Well, the disadvantage of the PostgreSQL way is that it keeps dead
rows
around for longer than they're actually needed, and so it causes some
problems in pathological conditions -- for example when setting up
large
replication sets with Slony, or during a pg_dump, no dead rows can be
removed. Since the Slony thing can take a very long time, dead rows
start to pile up in a way that can really harm performance.
In addition or rather, another potential issue, if you have a REALLY
long transaction running then you can risk transaction id wraparound.
Erik Jones
DBA | Emma®
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