Russell Smith wrote:
2. Index cleanup is the most expensive part of vacuum. So doing a partial vacuum actually means more I/O as you have to do index cleanup more often.

I don't think that's usually the case. Index(es) are typically only a fraction of the size of the table, and since 8.2 we do index vacuums in a single scan in physical order. In fact, in many applications the index is be mostly cached and the index scan doesn't generate any I/O at all.

I believe the heap scans are the biggest issue at the moment.

  Heikki Linnakangas

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