postgres_fdw join pushdown (was Re: Custom/Foreign-Join-APIs)

On Mon, Apr 27, 2015 at 5:07 AM, Shigeru Hanada
<shigeru(dot)hanada(at)gmail(dot)com> wrote:
> 2015-04-27 11:00 GMT+09:00 Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com>:
>> Hanada-san, could you adjust your postgres_fdw patch according to
>> the above new (previous?) definition.
>
> The attached v14 patch is the revised version for your v13 patch. It also contains changed for Ashutosh’s comments.

We should probably move this discussion to a new thread now that the
other patch is committed. Changing subject line accordingly.

Generally, there's an awful lot of changes in this patch - it is over
2000 insertions and more than 450 deletions - and it's not awfully
obvious why all of those changes are there. I think this patch needs
a detailed README to accompany it explaining what the various changes
in the patch are and why those things got changed; or maybe there is a
way to break it up into multiple patches so that we can take a more
incremental approach. I am really suspicious of the amount of
wholesale reorganization of code that this patch is doing. It's
really hard to validate that a reorganization like that is necessary,
or that it's correct, and it's gonna make back-patching noticeably
harder in the future. If we really need this much code churn it needs
careful justification; if we don't, we shouldn't do it.

+SET enable_mergejoin = off; -- planner choose MergeJoin even it has
higher costs, so disable it for testing.

This seems awfully strange. Why would the planner choose a plan if it
had a higher cost?

- * If the table or the server is configured to use remote estimates,
- * identify which user to do remote access as during planning. This
+ * Identify which user to do remote access as during planning. This
* should match what ExecCheckRTEPerms() does. If we fail due
to lack of
* permissions, the query would have failed at runtime anyway.
*/
- if (fpinfo->use_remote_estimate)
- {
- RangeTblEntry *rte = planner_rt_fetch(baserel->relid, root);
- Oid userid = rte->checkAsUser ?
rte->checkAsUser : GetUserId();
-
- fpinfo->user = GetUserMapping(userid, fpinfo->server->serverid);
- }
- else
- fpinfo->user = NULL;
+ rte = planner_rt_fetch(baserel->relid, root);
+ fpinfo->userid = rte->checkAsUser ? rte->checkAsUser : GetUserId();

So, wait a minute, remote estimates aren't optional any more?

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company