| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Treat <xzilla(at)users(dot)sourceforge(dot)net> |
| Cc: | Gaetano Mendola <mendola(at)bigfoot(dot)com>, pgsql-admin(at)postgresql(dot)org |
| Subject: | Re: Vacuum explained |
| Date: | 2003-01-06 20:45:59 |
| Message-ID: | 26423.1041885959@sss.pgh.pa.us |
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| Lists: | pgsql-admin |
Robert Treat <xzilla(at)users(dot)sourceforge(dot)net> writes:
> Tup = # of "rows" in your table
Right. This is the number of rows remaining after the vacuum, to be
precise.
> Keep = # of tuples that the db did not feel it could safely mark/remove
> (probably envolved in some type of transaction)
More specifically, these are tuples that are committed dead, but cannot
yet be removed because they might still be visible under the MVCC rules
to one or more open transactions. This number is included in "Tup".
> Unused = # of tuples awaiting being reused
These are not actually tuples, but tuple slots (page item pointers)
that are open for re-use.
regards, tom lane
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