Dear Hackers,

A gin index created on an initially empty table will never get used
until the table is vacuumed, which for a table with no update or
delete activity could be forever unless someone manually intervenes.


The problem is that numEntries in src/backend/utils/adt/selfuncs.c is
zero and eventually causes a division by zero and a cost estimate of
nan.

The code below does not save the day, because nTotalPages and
nEntryPages are 2 and 1 respectively when an index is created on an
empty table, or when an indexed table is truncated.

    if (ginStats.nTotalPages == 0 || ginStats.nEntryPages == 0)
    {
        numEntryPages = numPages;
        numDataPages = 0;
        numEntries = numTuples;     /* bogus, but no other info available */
    }

I don't know what the solution is.  Simply setting numEntries to 1 if
ginStats.nEntries zero solves this particular problem, but I don't
know what other consequences it might have.

Cheers,

Jeff

Responses

• Re: gincostestimate at 2011-04-21 23:27:22 from Tom Lane

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