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Add new replication mode synchronous_commit = 'remote_apply'.

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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.
This commit is contained in:
Robert Haas
2016-03-29 21:16:12 -04:00
parent a898b409f6
commit 314cbfc5da
16 changed files with 208 additions and 66 deletions
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5
src/backend/utils/misc/guc.c
View File

@ -345,12 +345,13 @@ static const struct config_enum_entry constraint_exclusion_options[] = {
};
/*
* Although only "on", "off", "remote_write", and "local" are documented, we
* accept all the likely variants of "on" and "off".
* Although only "on", "off", "remote_apply", "remote_write", and "local" are
* documented, we accept all the likely variants of "on" and "off".
*/
static const struct config_enum_entry synchronous_commit_options[] = {
{"local", SYNCHRONOUS_COMMIT_LOCAL_FLUSH, false},
{"remote_write", SYNCHRONOUS_COMMIT_REMOTE_WRITE, false},
{"remote_apply", SYNCHRONOUS_COMMIT_REMOTE_APPLY, false},
{"on", SYNCHRONOUS_COMMIT_ON, false},
{"off", SYNCHRONOUS_COMMIT_OFF, false},
{"true", SYNCHRONOUS_COMMIT_ON, true},

2
src/backend/utils/misc/postgresql.conf.sample
View File

@ -177,7 +177,7 @@
# (change requires restart)
#fsync = on # turns forced synchronization on or off
#synchronous_commit = on # synchronization level;
# off, local, remote_write, or on
# off, local, remote_write, remote_apply, or on
#wal_sync_method = fsync # the default is the first option
# supported by the operating system:
# open_datasync