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Fix some planning oversights in postgres_fdw.

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Include eval costs of local conditions in remote-estimate mode, and don't
assume the remote eval cost is zero in local-estimate mode.  (The best
we can do with that at the moment is to assume a seqscan, which may well
be wildly pessimistic ... but zero won't do at all.)

To get a reasonable local estimate, we need to know the relpages count
for the remote rel, so improve the ANALYZE code to fetch that rather
than just setting the foreign table's relpages field to zero.
This commit is contained in:
Tom Lane
2013-02-22 10:56:06 -05:00
parent af0a4c5924
commit c0c6acdfa0
3 changed files with 104 additions and 7 deletions
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23
contrib/postgres_fdw/deparse.c
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@ -456,6 +456,29 @@ appendWhereClause(StringInfo buf,
}
}
/*
* Construct SELECT statement to acquire size in blocks of given relation.
*
* Note: we use local definition of block size, not remote definition.
* This is perhaps debatable.
*
* Note: pg_relation_size() exists in 8.1 and later.
*/
void
deparseAnalyzeSizeSql(StringInfo buf, Relation rel)
{
Oid relid = RelationGetRelid(rel);
StringInfoData relname;
/* We'll need the remote relation name as a literal. */
initStringInfo(&relname);
deparseRelation(&relname, relid);
appendStringInfo(buf, "SELECT pg_catalog.pg_relation_size(");
deparseStringLiteral(buf, relname.data);
appendStringInfo(buf, "::pg_catalog.regclass) / %d", BLCKSZ);
}
/*
* Construct SELECT statement to acquire sample rows of given relation.
*