Horton

RE: [Proposal] Add foreign-server health checks infrastructure

Hayato Kuroda (Fujitsu) <kuroda.hayato@fujitsu.com>

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From: "kuroda.hayato@fujitsu.com" <kuroda.hayato@fujitsu.com>
To: 'Fujii Masao' <masao.fujii@oss.nttdata.com>
Cc: "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, 'Shinya Kato' <Shinya11.Kato@oss.nttdata.com>, "zyu@yugabyte.com" <zyu@yugabyte.com>
Date: 2022-02-02T12:37:42Z
Lists: pgsql-hackers

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Dear Fujii-san,

Thank you for good suggestions.

> This logic sounds complicated to me. I'm afraid that FDW developers may a bit
> easily misunderstand the logic and make the bug in their FDW.
> Isn't it simpler to just disable the timeout in core whenever the transaction ends
> whether committed or aborted, like statement_timeout is disabled after each
> command? For example, call something like DisableForeignCheckTimeout() in
> CommitTransaction() etc.

Your idea is that stop the timer at the end of each transactions, right?
I had not adopted that because I thought some developers might want not to stop the timer
even if transactions ends. It caused complexed situation and not have good usecase, however,
so your logic was implemented.

> > You are right. I think this suggests that error-reporting should be done in the
> core layer.
> > For meaningful error reporting, I changed a callback specification
> > that it should return ForeignServer* which points to downed remote server.
> 
> This approach seems to assume that FDW must manage all the ForeignServer
> information so that the callback can return it. Is this assumption valid for all the
> FDW?

Not sure, the assumption might be too optimistic. 
mysql_fdw can easily return ForeignServer* because it caches serverid,
but dblink and maybe oracle_fdw cannot.

> How about making FDW trigger a query cancel interrupt by signaling SIGINT to
> the backend, instead?

I understood that the error should be caught by QueryCancelPending.
Could you check 0003? Does it follow that?

Best Regards,
Hayato Kuroda
FUJITSU LIMITED

Commits

  1. postgres_fdw: Extend postgres_fdw_get_connections to return user name.

  2. postgres_fdw: Fix bug in connection status check.

  3. postgres_fdw: Add connection status check to postgres_fdw_get_connections().

  4. postgres_fdw: Add "used_in_xact" column to postgres_fdw_get_connections().

  5. doc: Enhance documentation for postgres_fdw_get_connections() output columns.

  6. Avoid reference to nonexistent array element in ExecInitAgg().

  7. Add WL_SOCKET_CLOSED for socket shutdown events.

  8. postgres_fdw: reestablish new connection if cached one is detected as broken.