On 09.08.2012 14:11, Simon Riggs wrote:
Given the marginal gain because of a low percentage of cross-block
updates, I'm not keen. Low percentage because HOT tries hard to keep
things on same block - even for non-HOT updates (which is the case,
even though it sounds weird).
That depends entirely on the workload. If you do a bulk update that
updates every row on the table, most are going to be cross-block
updates, and the WAL size does matter.
But then again, full-page writes cover that too. There
will be a full-page image of the old block in the WAL anyway.
Right, but we're planning to remove that, so its not a safe assumption
to use when building new code.
I don't think we're going to get rid of full-page images any time soon.
I guess you could easily check if full-page writes are enabled, though,
and only do it for cross-page updates if it is.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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