On Sat, Jun 7, 2014 at 1:28 AM, Andres Freund <and...@2ndquadrant.com> wrote: > > On 2014-06-06 15:44:25 -0400, Tom Lane wrote: > > I figured it'd be easy enough to get a better estimate by adding another > > counter to count just LIVE and INSERT_IN_PROGRESS tuples (thus effectively > > assuming that in-progress inserts and deletes will both commit). I did > > that, and found that it helped Tim's test case not at all :-(. A bit of > > sleuthing revealed that HeapTupleSatisfiesVacuum actually returns > > INSERT_IN_PROGRESS for any tuple whose xmin isn't committed, regardless of > > whether the transaction has since marked it for deletion: > > > > /* > > * It'd be possible to discern between INSERT/DELETE in progress > > * here by looking at xmax - but that doesn't seem beneficial for > > * the majority of callers and even detrimental for some. We'd > > * rather have callers look at/wait for xmin than xmax. It's > > * always correct to return INSERT_IN_PROGRESS because that's > > * what's happening from the view of other backends. > > */ > > return HEAPTUPLE_INSERT_IN_PROGRESS; > > That's only the case of a couple of days ago. I really wasn't sure > wheter to go that way or discern the two cases. That changed in the wake > of: > http://www.postgresql.org/message-id/20140530143150.GA11051@localhost
Won't this change impact the calculation of number of live rows for analyze (acquire_sample_rows() considers the HEAPTUPLE_DELETE_IN_PROGRESS tuples as liverows for tuples updated by transactions other than current transaction)? Even if we think that estimates are okay, the below comment in acquire_same_rows() doesn't seem to suggest it. /* * We count delete-in-progress rows as still live, using * the same reasoning given above; but we don't bother to * include them in the sample. * .. */ With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
