Re: Sync Rep for 2011CF1
От | Simon Riggs |
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Тема | Re: Sync Rep for 2011CF1 |
Дата | |
Msg-id | 1295703074.1803.19835.camel@ebony обсуждение исходный текст |
Ответ на | Re: Sync Rep for 2011CF1 (Robert Haas <robertmhaas@gmail.com>) |
Ответы |
Re: Sync Rep for 2011CF1
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Список | pgsql-hackers |
On Fri, 2011-01-21 at 13:32 -0500, Robert Haas wrote: > One idea might be to wait both before and after commit. If > allow_standalone_primary is off, and a commit is attempted, we check > whether there's a slave connected, and if not, wait for one to > connect. Then, we write and sync the commit WAL record. Next, we > wait for the WAL to be ack'd. Of course, the standby might disappear > between the first check and the second, but it would greatly reduce > the possibility of the master being ahead of the standby after a > crash, which might be useful for some people. I like this idea. I think it would be too invasive to make a check before we insert each WAL record, as Aidan suggests. Even if we did that, you aren't protected when a standby goes down because you'll still have written half a transaction and still be waiting. So I propose that if (!allow_standalone_primary) ConfirmSyncRepAvailable(); before PreCommit_Notify(). That puts transaction into a wait state that lasts until a sync rep standby is available. Note that it is before the actual commit, so if we decide we need to we can cancel those transactions and have them properly abort. I won't add that code yet, in case better ideas emerge. There is no support for preventing connections at startup, so I will remove that completely, now. -- Simon Riggs http://www.2ndQuadrant.com/books/PostgreSQL Development, 24x7 Support, Training and Services
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