pgsql: Add new replication mode synchronous_commit = 'remote_apply'.
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.
Branch
------
master
Details
-------
http://git.postgresql.org/pg/commitdiff/314cbfc5da988eff8998655158f84c9815ecfbcd
Modified Files
--------------
doc/src/sgml/config.sgml | 14 ++--
doc/src/sgml/high-availability.sgml | 18 ++++-
src/backend/access/transam/twophase.c | 6 +-
src/backend/access/transam/xact.c | 16 +++-
src/backend/access/transam/xlog.c | 23 ++++++
src/backend/replication/README | 18 +++--
.../libpqwalreceiver/libpqwalreceiver.c | 26 +++----
src/backend/replication/syncrep.c | 35 +++++++--
src/backend/replication/walreceiver.c | 85 ++++++++++++++++++----
src/backend/utils/misc/guc.c | 5 +-
src/backend/utils/misc/postgresql.conf.sample | 2 +-
src/include/access/xact.h | 7 +-
src/include/access/xlog.h | 2 +
src/include/access/xlog_internal.h | 2 +-
src/include/replication/syncrep.h | 5 +-
src/include/replication/walreceiver.h | 12 ++-
16 files changed, 209 insertions(+), 67 deletions(-)
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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.
--
Michael
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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.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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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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On Tue, Mar 29, 2016 at 9:43 PM, Michael Paquier
<michael.paquier@gmail.com> wrote:
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.
Yeah, I'd be very surprised if anyone did that.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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