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To: [email protected] <[email protected]>
To: 'Önder Kalacı' <[email protected]>
To: Fujii Masao <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: [email protected] <[email protected]>
Cc: [email protected] <[email protected]>
Cc: [email protected] <[email protected]>
Cc: Kyotaro Horiguchi <[email protected]>
Subject: RE: [Proposal] Add foreign-server health checks infrastructure
Date: Mon, 17 Oct 2022 12:25:21 +0000
Message-ID: <TYAPR01MB5866E2788F327896D2AF4E42F5299@TYAPR01MB5866.jpnprd01.prod.outlook.com> (raw)
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Dear Osumi-san,
> I mainly followed the steps there and
> replaced the command "SELECT" for the remote table at 6-9 with "INSERT"
> command.
> Then, after waiting for few seconds, the "COMMIT" succeeded like below output,
> even after the server stop of the worker side.
> Additionally, the last reference "SELECT" which failed above can succeed,
> if I restart the worker server before the "SELECT" command to the remote table.
> This means the transaction looks successful but the data isn't there ?
> Could you please have a look at this issue ?
Good catch. This was occurred because we disconnected the crashed server.
Previously the failed server had been disconnected in the pgfdw_connection_check().
It was OK if the transaction(or statement) was surely cacneled.
But currently the statement might be not canceled because QueryCancelPending might be cleaned up[1].
If we failed to cancel statements and reached pgfdw_xact_callback(),
the connection would not be used because entry->conn is NULL.
That's why you sucseeded to do "COMMIT".
However, the backend did not send "COMMIT" command to the srever,
so inserted data was vanished on remote server.
I understood that we should not call disconnect_pg_server(entry->conn) even if we detect the disconnection.
If should be controlled in Xact callback. This will be modified in next version.
Moreover, I noticed that we should enable timer even if the QueryCancelMessage was not NULL.
If we do not turn on here, the checking will be never enabled again.
[1]: https://www.postgresql.org/message-id/TYAPR01MB5866CE34430424A588F60FC2F55D9%40TYAPR01MB5866.jpnprd0...
Best Regards,
Hayato Kuroda
FUJITSU LIMITED
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Subject: RE: [Proposal] Add foreign-server health checks infrastructure
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