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Merge synchronous_replication setting into synchronous_commit. 

This means one less thing to configure when setting up synchronous
replication, and also avoids some ambiguity around what the behavior
should be when the settings of these variables conflict.

Fujii Masao, with additional hacking by me.
This commit is contained in:
Robert Haas 2011-04-04 16:13:01 -04:00
parent fc3459d70c
commit 240067b3b0
10 changed files with 91 additions and 104 deletions
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68
doc/src/sgml/config.sgml
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@ -1507,8 +1507,9 @@ SET ENABLE_SEQSCAN TO OFF;
<para>
Specifies whether transaction commit will wait for WAL records
to be written to disk before the command returns a <quote>success</>
indication to the client. The default, and safe, setting is
<literal>on</>. When <literal>off</>, there can be a delay between
indication to the client. Valid values are <literal>on</>,
<literal>local</>, and <literal>off</>. The default, and safe, value
is <literal>on</>. When <literal>off</>, there can be a delay between
when success is reported to the client and when the transaction is
really guaranteed to be safe against a server crash. (The maximum
delay is three times <xref linkend="guc-wal-writer-delay">.) Unlike
@ -1522,6 +1523,19 @@ SET ENABLE_SEQSCAN TO OFF;
exact certainty about the durability of a transaction. For more
discussion see <xref linkend="wal-async-commit">.
</para>
<para>
If <xref linkend="guc-synchronous-standby-names"> is set, this
parameter also controls whether or not transaction commit will wait
for the transaction's WAL records to be flushed to disk and replicated
to the standby server. The commit wait will last until a reply from
the current synchronous standby indicates it has written the commit
record of the transaction to durable storage. If synchronous
replication is in use, it will normally be sensible either to wait
both for WAL records to reach both the local and remote disks, or
to allow the transaction to commit asynchronously. However, the
special value <literal>local</> is available for transactions that
wish to wait for local flush to disk, but not synchronous replication.
</para>
<para>
This parameter can be changed at any time; the behavior for any
one transaction is determined by the setting in effect when it
@ -2057,39 +2071,6 @@ SET ENABLE_SEQSCAN TO OFF;
</para>
<variablelist>
<varlistentry id="guc-synchronous-replication" xreflabel="synchronous_replication">
<term><varname>synchronous_replication</varname> (<type>boolean</type>)</term>
<indexterm>
<primary><varname>synchronous_replication</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
Specifies whether transaction commit will wait for WAL records
to be replicated before the command returns a <quote>success</>
indication to the client. The default setting is <literal>off</>.
When <literal>on</>, there will be a delay while the client waits
for confirmation of successful replication. That delay will
increase depending upon the physical distance and network activity
between primary and standby. The commit wait will last until a
reply from the current synchronous standby indicates it has written
the commit record of the transaction to durable storage. This
parameter has no effect if
<xref linkend="guc-synchronous-standby-names"> is empty or
<xref linkend="guc-max-wal-senders"> is zero.
</para>
<para>
This parameter can be changed at any time; the
behavior for any one transaction is determined by the setting in
effect when it commits. It is therefore possible, and useful, to have
some transactions replicate synchronously and others asynchronously.
For example, to make a single multistatement transaction commit
asynchronously when the default is synchronous replication, issue
<command>SET LOCAL synchronous_replication TO OFF</> within the
transaction.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-synchronous-standby-names" xreflabel="synchronous_standby_names">
<term><varname>synchronous_standby_names</varname> (<type>string</type>)</term>
<indexterm>
@ -2098,7 +2079,7 @@ SET ENABLE_SEQSCAN TO OFF;
<listitem>
<para>
Specifies a priority ordered list of standby names that can offer
synchronous replication. At any one time there will be just one
synchronous replication. At any one time there will be at most one
synchronous standby that will wake sleeping users following commit.
The synchronous standby will be the first named standby that is
both currently connected and streaming in real-time to the standby
@ -2114,18 +2095,17 @@ SET ENABLE_SEQSCAN TO OFF;
not enforced for uniqueness. In case of duplicates one of the standbys
will be chosen to be the synchronous standby, though exactly which
one is indeterminate.
</para>
<para>
No value is set by default.
The special entry <literal>*</> matches any application_name, including
the default application name of <literal>walreceiver</>.
</para>
<para>
If a standby is removed from the list of servers then it will stop
being the synchronous standby, allowing another to take its place.
If the list is empty, synchronous replication will not be
possible, whatever the setting of <varname>synchronous_replication</>.
Standbys may also be added to the list without restarting the server.
If no synchronous standby names are specified, then synchronous
replication is not enabled and transaction commit will never wait for
replication. This is the default configuration. Even when
synchronous replication is enabled, individual transactions can be
configured not to wait for replication by setting the
<xref linkend="guc-synchronous-commit"> parameter to
<literal>local</> or <literal>off</>.
</para>
</listitem>
</varlistentry>

48
doc/src/sgml/high-availability.sgml
View File

@ -929,19 +929,18 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
<title>Basic Configuration</title>
<para>
All parameters have useful default values, so we can enable
synchronous replication easily just by setting this on the primary:
<programlisting>
synchronous_replication = on
</programlisting>
When <varname>synchronous_replication</> is set, a commit will wait
for confirmation that the standby has received the commit record,
even if that takes a very long time.
<varname>synchronous_replication</> can be set by individual
Once streaming replication has been configured, configuring synchronous
replication requires only one additional configuration step:
<xref linkend="guc-synchronous-standby-names"> must be set to
a non-empty value. <varname>synchronous_commit</> must also be set to
<literal>on</>, but since this is the default value, typically no change is
required. This configuration will cause each commit to wait for
confirmation that the standby has written the commit record to durable
storage, even if that takes a very long time.
<varname>synchronous_commit</> can be set by individual
users, so can be configured in the configuration file, for particular
users or databases, or dynamically by applications.
users or databases, or dynamically by applications, in order to control
the durability guarantee on a per-transaction basis.
</para>
<para>
@ -959,17 +958,10 @@ synchronous_replication = on
</para>
<para>
Users will stop waiting if a fast shutdown is requested, though the
server does not fully shutdown until all outstanding WAL records are
transferred to standby servers.
</para>
<para>
Note also that <varname>synchronous_commit</> is used when the user
specifies <varname>synchronous_replication</>, overriding even an
explicit setting of <varname>synchronous_commit</> to <literal>off</>.
This is because we must write WAL to disk on primary before we replicate
to ensure the standby never gets ahead of the primary.
Users will stop waiting if a fast shutdown is requested. However, as
when using asynchronous replication, the server will does not fully
shutdown until all outstanding WAL records are transferred to the currently
connected standby servers.
</para>
</sect3>
@ -1019,9 +1011,9 @@ synchronous_replication = on
<title>Planning for High Availability</title>
<para>
Commits made when synchronous_replication is set will wait until
the sync standby responds. The response may never occur if the last,
or only, standby should crash.
Commits made when <varname>synchronous_commit</> is set to <literal>on</>
will wait until the sync standby responds. The response may never occur
if the last, or only, standby should crash.
</para>
<para>
@ -1073,8 +1065,8 @@ synchronous_replication = on
If you need to re-create a standby server while transactions are
waiting, make sure that the commands to run pg_start_backup() and
pg_stop_backup() are run in a session with
synchronous_replication = off, otherwise those requests will wait
forever for the standby to appear.
<varname>synchronous_commit</> = <literal>off</>, otherwise those
requests will wait forever for the standby to appear.
</para>
</sect3>

7
doc/src/sgml/release-9.1.sgml
View File

@ -651,14 +651,15 @@
</para>
<para>
This allows the primary to wait for a standby to write the transaction
information to disk before acknowledging the commit.
One standby at a time can take the role of the synchronous standby,
as controlled by the
<link linkend="guc-synchronous-standby-names"><varname>synchronous_standby_names</varname></link>
setting. Synchronous replication can be enabled or disabled on a
per-transaction basis using the
<link linkend="guc-synchronous-replication"><varname>synchronous_replication</></link>
setting. This allows the primary to wait for a standby to write the
transaction information to disk before acknowledging the commit.
<link linkend="guc-synchronous-commit"><varname>synchronous_commit</></link>
setting.
</para>
</listitem>

5
src/backend/access/transam/xact.c
View File

@ -68,7 +68,7 @@ bool XactReadOnly;
bool DefaultXactDeferrable = false;
bool XactDeferrable;
bool XactSyncCommit = true;
int synchronous_commit = SYNCHRONOUS_COMMIT_ON;
int CommitDelay = 0; /* precommit delay in microseconds */
int CommitSiblings = 5; /* # concurrent xacts needed to sleep */
@ -1056,7 +1056,8 @@ RecordTransactionCommit(void)
* if all to-be-deleted tables are temporary though, since they are lost
* anyway if we crash.)
*/
if ((wrote_xlog && XactSyncCommit) || forceSyncCommit || nrels > 0 || SyncRepRequested())
if ((wrote_xlog && synchronous_commit >= SYNCHRONOUS_COMMIT_LOCAL) ||
forceSyncCommit || nrels > 0)
{
/*
* Synchronous commit case:

3
src/backend/postmaster/autovacuum.c
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@ -1531,7 +1531,8 @@ AutoVacWorkerMain(int argc, char *argv[])
* if we are waiting for standbys to connect. This is important to
* ensure we aren't blocked from performing anti-wraparound tasks.
*/
SetConfigOption("synchronous_replication", "off", PGC_SUSET, PGC_S_OVERRIDE);
if (synchronous_commit == SYNCHRONOUS_COMMIT_ON)
SetConfigOption("synchronous_commit", "local", PGC_SUSET, PGC_S_OVERRIDE);
/*
* Get the info about the database we're going to work on.

1
src/backend/replication/syncrep.c
View File

@ -63,7 +63,6 @@
#include "utils/ps_status.h"
/* User-settable parameters for sync rep */
bool synchronous_replication = false; /* Only set in user backends */
char *SyncRepStandbyNames;
#define SyncStandbysDefined() \

43
src/backend/utils/misc/guc.c
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@ -350,6 +350,23 @@ static const struct config_enum_entry constraint_exclusion_options[] = {
{NULL, 0, false}
};
/*
* Although only "on", "off", 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, false},
{"on", SYNCHRONOUS_COMMIT_ON, false},
{"off", SYNCHRONOUS_COMMIT_OFF, false},
{"true", SYNCHRONOUS_COMMIT_ON, true},
{"false", SYNCHRONOUS_COMMIT_OFF, true},
{"yes", SYNCHRONOUS_COMMIT_ON, true},
{"no", SYNCHRONOUS_COMMIT_OFF, true},
{"1", SYNCHRONOUS_COMMIT_ON, true},
{"0", SYNCHRONOUS_COMMIT_OFF, true},
{NULL, 0, false}
};
/*
* Options for enum values stored in other modules
*/
@ -746,22 +763,6 @@ static struct config_bool ConfigureNamesBool[] =
&enableFsync,
true, NULL, NULL
},
{
{"synchronous_commit", PGC_USERSET, WAL_SETTINGS,
gettext_noop("Sets immediate fsync at commit."),
NULL
},
&XactSyncCommit,
true, NULL, NULL
},
{
{"synchronous_replication", PGC_USERSET, WAL_REPLICATION,
gettext_noop("Requests synchronous replication."),
NULL
},
&synchronous_replication,
false, NULL, NULL
},
{
{"zero_damaged_pages", PGC_SUSET, DEVELOPER_OPTIONS,
gettext_noop("Continues processing past damaged page headers."),
@ -2908,6 +2909,16 @@ static struct config_enum ConfigureNamesEnum[] =
assign_session_replication_role, NULL
},
{
{"synchronous_commit", PGC_USERSET, WAL_SETTINGS,
gettext_noop("Sets the current transaction's synchronization level."),
NULL
},
&synchronous_commit,
SYNCHRONOUS_COMMIT_ON, synchronous_commit_options,
NULL, NULL
},
{
{"trace_recovery_messages", PGC_SIGHUP, DEVELOPER_OPTIONS,
gettext_noop("Enables logging of recovery-related debugging information."),

6
src/backend/utils/misc/postgresql.conf.sample
View File

@ -153,7 +153,7 @@
#wal_level = minimal # minimal, archive, or hot_standby
# (change requires restart)
#fsync = on # turns forced synchronization on or off
#synchronous_commit = on # immediate fsync at commit
#synchronous_commit = on # synchronization level; on, off, or local
#wal_sync_method = fsync # the default is the first option
# supported by the operating system:
# open_datasync
@ -184,10 +184,6 @@
#archive_timeout = 0 # force a logfile segment switch after this
# number of seconds; 0 disables
# - Replication - User Settings
#synchronous_replication = off # does commit wait for reply from standby
# - Streaming Replication - Server Settings
#synchronous_standby_names = '' # standby servers that provide sync rep

11
src/include/access/xact.h
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@ -52,8 +52,15 @@ extern bool XactReadOnly;
extern bool DefaultXactDeferrable;
extern bool XactDeferrable;
/* Asynchronous commits */
extern bool XactSyncCommit;
typedef enum
{
SYNCHRONOUS_COMMIT_OFF, /* asynchronous commit */
SYNCHRONOUS_COMMIT_LOCAL, /* wait for only local flush */
SYNCHRONOUS_COMMIT_ON /* wait for local flush and sync rep */
} SyncCommitLevel;
/* Synchronous commit level */
extern int synchronous_commit;
/* Kluge for 2PC support */
extern bool MyXactAccessedTempRel;

3
src/include/replication/syncrep.h
View File

@ -20,7 +20,7 @@
#include "utils/guc.h"
#define SyncRepRequested() \
(synchronous_replication && max_wal_senders > 0)
(max_wal_senders > 0 && synchronous_commit == SYNCHRONOUS_COMMIT_ON)
/* syncRepState */
#define SYNC_REP_NOT_WAITING 0
@ -28,7 +28,6 @@
#define SYNC_REP_WAIT_COMPLETE 2
/* user-settable parameters for synchronous replication */
extern bool synchronous_replication;
extern char *SyncRepStandbyNames;
/* called by user backend */