database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-06-14 18:42:34 +03:00
Code Activity

Allow FDWs and custom scan providers to replace joins with scans.

Browse Source 
Foreign data wrappers can use this capability for so-called "join
pushdown"; that is, instead of executing two separate foreign scans
and then joining the results locally, they can generate a path which
performs the join on the remote server and then is scanned locally.
This commit does not extend postgres_fdw to take advantage of this
capability; it just provides the infrastructure.

Custom scan providers can use this in a similar way.  Previously,
it was only possible for a custom scan provider to scan a single
relation.  Now, it can scan an entire join tree, provided of course
that it knows how to produce the same results that the join would
have produced if executed normally.

KaiGai Kohei, reviewed by Shigeru Hanada, Ashutosh Bapat, and me.
This commit is contained in:
Robert Haas
2015-05-01 08:50:35 -04:00
parent 2b22795b32
commit e7cb7ee145
20 changed files with 448 additions and 71 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
src/backend/executor/execScan.c
View File

@ -251,6 +251,12 @@ ExecAssignScanProjectionInfo(ScanState *node)
/* Vars in an index-only scan's tlist should be INDEX_VAR */
if (IsA(scan, IndexOnlyScan))
varno = INDEX_VAR;
/* Also foreign or custom scan on pseudo relation should be INDEX_VAR */
else if (scan->scanrelid == 0)
{
Assert(IsA(scan, ForeignScan) || IsA(scan, CustomScan));
varno = INDEX_VAR;
}
else
varno = scan->scanrelid;