Re: [HACKERS] Hot Standby and cancelling idle queries
On Wednesday 25 November 2009 17:25:43 Tom Lane wrote: Simon Riggs si...@2ndquadrant.com writes: An idle-in-transaction transaction can also hold a temporary file. Think of an open cursor, for example. Therefore, remove the distinction between CONFLICT_MODE_ERROR and CONFLICT_MODE_ERROR_IF_NOT_IDLE, idle-in-transaction backends need to be killed too when a tablespace is dropped. Um ... I think you have forgotten about WITH HOLD cursors, which will also have temp files. Implication: whatever you are thinking of here would require killing EVERY session. Conclusion: you need a different design. Actually WITH HOLD cursors should not pose a problem - the code already tries to handle that: In fd.c:OpenTemporaryFile: * BUT: if the temp file is slated to outlive the current transaction, * force it into the database's default tablespace, so that it will not * pose a threat to possible tablespace drop attempts. */ Whether thats generally a good idea is another question. Andres -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Hot Standby and cancelling idle queries
On Thu, 2009-11-26 at 08:30 +0200, Heikki Linnakangas wrote: I suspect you missed the context of this change. It's about the code in tablespc.c, to kill all backends that might have a temporary file in a tablespace that's being dropped. It's not about tuple visibility but temporary files. Got you now. -- Simon Riggs www.2ndQuadrant.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
[HACKERS] Hot Standby and cancelling idle queries
Recent change: An idle-in-transaction transaction can also hold a temporary file. Think of an open cursor, for example. Therefore, remove the distinction between CONFLICT_MODE_ERROR and CONFLICT_MODE_ERROR_IF_NOT_IDLE, idle-in-transaction backends need to be killed too when a tablespace is dropped. Open cursors still have snapshots, so they would not be treated as idle in transaction. If the user has a held cursor then they can keep it, since it has already read the database and released the snapshot. So this change seems both unnecessary and harsh, since even if it is necessary we can work out how to avoid this easily enough. -- Simon Riggs www.2ndQuadrant.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Hot Standby and cancelling idle queries
Simon Riggs si...@2ndquadrant.com writes: An idle-in-transaction transaction can also hold a temporary file. Think of an open cursor, for example. Therefore, remove the distinction between CONFLICT_MODE_ERROR and CONFLICT_MODE_ERROR_IF_NOT_IDLE, idle-in-transaction backends need to be killed too when a tablespace is dropped. Um ... I think you have forgotten about WITH HOLD cursors, which will also have temp files. Implication: whatever you are thinking of here would require killing EVERY session. Conclusion: you need a different design. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Hot Standby and cancelling idle queries
Simon Riggs wrote: Recent change: An idle-in-transaction transaction can also hold a temporary file. Think of an open cursor, for example. Therefore, remove the distinction between CONFLICT_MODE_ERROR and CONFLICT_MODE_ERROR_IF_NOT_IDLE, idle-in-transaction backends need to be killed too when a tablespace is dropped. Open cursors still have snapshots, so they would not be treated as idle in transaction. A backend is idle-in-transaction whenever a transaction is open and the backend is waiting for a command from the client. Whether it has active snapshots or open cursors doesn't affect that. If the user has a held cursor then they can keep it, since it has already read the database and released the snapshot. A held cursor can keep a temp file open. I suspect you missed the context of this change. It's about the code in tablespc.c, to kill all backends that might have a temporary file in a tablespace that's being dropped. It's not about tuple visibility but temporary files. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
