Message-ID: <4E9D126F.5010508@lab.ntt.co.jp>
Date: Tue, 18 Oct 2011 14:45:19 +0900
From: Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>
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To: Shigeru Hanada <shigeru.hanada@gmail.com>
CC: pgsql-hackers@postgresql.org
Subject: Re: WIP: Collecting statistics on CSV file data
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(2011/10/18 2:27), Shigeru Hanada wrote:
> The new patch could be applied with some shifts.  Regression tests of
> core and file_fdw have passed cleanly.  Though I've tested only simple
> tests, ANALYZE works for foreign tables for file_fdw, and estimation of
> costs and selectivity seem appropriate.

Thank you for your testing.

> New API AnalyzeForeignTable
> ===========================

> And I think that AnalyzeForeignTable should be optional, and it would be
> very useful if a default handler is provided.  Probably a default
> handler can use basic FDW APIs to acquire sample rows from the result of
> "SELECT * FROM foreign_table" with skipping periodically.  It won't be
> efficient but I think it's not so unreasonable.

I agree with you. However, I think that it is difficult to support such
a default handler in a unified way because there exist external data
sources for which we cannot execute "SELECT * FROM foreign_table", e.g.,
web-accessible DBs limiting full access to the contents.

> Other issues
> ============
> There are some other comments about non-critical issues.
> - When there is no analyzable column, vac_update_relstats is not called.
>   Is this behavior intentional?
> - psql can't complete foreign table name after ANALYZE.
> - A new parameter has been added to vac_update_relstats in a recent
> commit.  Perhaps 0 is OK for that parameter.

I'll check.

> - ANALYZE without relation name ignores foreign tables because
> get_rel_oids doesn't list foreign tables.

I think that it might be better to ignore foreign tables by default
because analyzing such tables may take long depending on FDW.

> - IMO logging "analyzing foo.bar" should not be done in
> AnalyzeForeignTable handler of each FDW because some FDW might forget to
> do it.  Maybe it should be pulled up to analyze_rel or somewhere in core.
> - It should be mentioned in a document that foreign tables are not
> analyzed automatically because they are read-only.

OK. I'll revise.

> Regards,

Best regards,
Etsuro Fujita