Re: [HACKERS] get_relation_stats_hook()

Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> New version of Postgres patch, v5. Implements suggested changes.
> Ready for review and apply.

Applied with some revisions. The method for passing back freefunc
didn't work, so I made it pass the whole VariableStatsData struct
instead; this might allow some additional flexibility by changing other
fields besides the intended statsTuple and freefunc. Also, I was still
unhappy about adding a hook in the midst of code that clearly needs
improvement, without making it possible for the hook to override the
adjacent broken code paths; so I refactored the API a bit for that too.

The plugin function would now be something like this:

static bool
plugin_get_relation_stats(PlannerInfo *root,
RangeTblEntry *rte,
AttrNumber attnum,
VariableStatData *vardata)
{
HeapTuple statstup = NULL;

/* For now, we only cover the simple-relation case */
if (rte->rtekind != RTE_RELATION || rte->inh)
return false;

if (!get_tom_stats_tupletable(rte->relid, attnum))
return false;

/*
* Get stats if present. We asked for only one row, so no need for loops.
*/
if (SPI_processed > 0)
statstup = SPI_copytuple(SPI_tuptable->vals[0]);

SPI_freetuptable(SPI_tuptable);
SPI_finish();

if (!statstup)
return false; /* should this happen? */

vardata->statsTuple = statstup;
/* define function to use when time to free the tuple */
vardata->freefunc = heap_freetuple;

return true;
}

and if you want to insert stats for expression indexes then there's a
separate get_index_stats_hook for that.

regards, tom lane