09.01.2014 05:15, Peter Eisentraut kirjoitti:
pg_upgrade creates a script analyze_new_cluster.{sh|bat} that runs
vacuumdb --analyze-only in three stages with different statistics target
settings to get a fresh cluster analyzed faster. I think this behavior
is also useful for clusters or databases freshly created by pg_restore
or any other loading mechanism, so it's suboptimal to have this
constrained to pg_upgrade.
I think the three stage analyze is a wrong solution to the "slow
analyze" problem. In my experience most of the analyze time goes to
reading random blocks from the disk but we usually use only a small
portion of that data (1 row per block.)
If we were able to better utilize the data we read we could get good
statistics with a lot less IO than we currently need. This was
discussed in length at
http://www.postgresql.org/message-id/CAM-w4HOjRbNPMW=shjhw_qfapcuu5ege1tmdr0zqu+kqx8q...@mail.gmail.com
but it hasn't turned into patches so far.
/ Oskari
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