Re: pgsql: Add new replication mode synchronous_commit = 'remote_apply'.
От | Michael Paquier |
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Тема | Re: pgsql: Add new replication mode synchronous_commit = 'remote_apply'. |
Дата | |
Msg-id | CAB7nPqR3pedustYhF2USocFhs9ON=8XucRo-SU2=oJ4LszSB2A@mail.gmail.com обсуждение исходный текст |
Ответ на | Re: pgsql: Add new replication mode synchronous_commit = 'remote_apply'. (Robert Haas <robertmhaas@gmail.com>) |
Ответы |
Re: pgsql: Add new replication mode synchronous_commit = 'remote_apply'.
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Список | pgsql-committers |
On Wed, Mar 30, 2016 at 10:39 AM, Robert Haas <robertmhaas@gmail.com> wrote: > On Tue, Mar 29, 2016 at 9:37 PM, Michael Paquier > <michael.paquier@gmail.com> wrote: >> On Wed, Mar 30, 2016 at 10:31 AM, Robert Haas <rhaas@postgresql.org> wrote: >>> Add new replication mode synchronous_commit = 'remote_apply'. >>> >>> In this mode, the master waits for the transaction to be applied on >>> the remote side, not just written to disk. That means that you can >>> count on a transaction started on the standby to see all commits >>> previously acknowledged by the master. >>> >>> To make this work, the standby sends a reply after replaying each >>> commit record generated with synchronous_commit >= 'remote_apply'. >>> This introduces a small inefficiency: the extra replies will be sent >>> even by standbys that aren't the current synchronous standby. But >>> previously-existing synchronous_commit levels make no attempt at all >>> to optimize which replies are sent based on what the primary cares >>> about, so this is no worse, and at least avoids any extra replies for >>> people not using the feature at all. >>> >>> Thomas Munro, reviewed by Michael Paquier and by me. Some additional >>> tweaks by me. >> >> The commit message does not directly mention that the spec of >> walrcv_receive has been changed in a backward-incompatible way so as >> the wait control can be done with a latch directly in walreceiver.c >> and not in libpqwalreceiver.c. That's not worth a mention in the >> release notes as this is really low-level and compilation on any code >> using this hook would simply fail on 9.6, so I am just mentioning it >> for the sake of the archives. > > Yeah, I didn't really think that mattered much. I'm not really sure > what you even mean by backward-incompatible -- AFAIK, that's a private > interface which we can whack around whenever we like. By "Backward-incompatible", I mean that any custom library using this walrcv hook is not going to compile anymore and we don't provide a pre-9.5 equivalent. I don't think that's worth worrying though, I have yet to see this interface being used for something else than libpqwalreceiver to be honest. -- Michael
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