Обсуждение: Get relid for a relation

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Get relid for a relation

От
Amin
Дата:
Hi,

In CustomScan cost estimator, where PlannerInfo and RelOptInfo are passed, I want to get access to the relation stats (for example pg_stat_all_tables) by calling pg_stat_fetch_stat_tabentry(). However, I don't have access to relid to pass to this function. For a sample relation, when I hardcode the relid (for example 16385), it works. However, RelOptInfo->relid is always 1 (for whatever relation the query is scanning). Why this happens and how to get access to the correct relid (16385) as in pg_stat_all_tables?

Thank you!

Re: Get relid for a relation

От
Tom Lane
Дата:
Amin <amin.fallahi@gmail.com> writes:
> In CustomScan cost estimator, where PlannerInfo and RelOptInfo are passed,
> I want to get access to the relation stats (for example pg_stat_all_tables)
> by calling pg_stat_fetch_stat_tabentry(). However, I don't have access to
> relid to pass to this function.

Sure you do.  The existing code, eg in selfuncs.c, does it about like
this:

        RangeTblEntry *rte = planner_rt_fetch(rel->relid, root);

        Assert(rte->rtekind == RTE_RELATION);
        relid = rte->relid;
        Assert(relid != InvalidOid);
        ...
        vardata.statsTuple = SearchSysCache3(STATRELATTINH,
                                             ObjectIdGetDatum(relid),
                                             Int16GetDatum(colnum),
                                             BoolGetDatum(rte->inh));

This is maybe a bit confusing, in that rel->relid is a range
table index but rte->relid is an OID.

FWIW, I seriously doubt that the numbers kept by the pg_stat mechanisms
are what you want for query planning purposes.

            regards, tom lane