Manage Journaling
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MongoDB uses write ahead logging to an on-disk journal to guarantee write operation durability.
The WiredTiger storage engine does not require journaling to guarantee a consistent state after a crash. The database will be restored to the last consistent checkpoint during recovery. However, if MongoDB exits unexpectedly in between checkpoints, journaling is required to recover writes that occurred after the last checkpoint.
Note
Starting in MongoDB 4.0, you cannot specify --nojournal
option or storage.journal.enabled:
false
for replica set members that use the
WiredTiger storage engine.
With journaling enabled, if mongod
stops unexpectedly, the
program can recover everything written to the journal. MongoDB will
re-apply the write operations on restart and maintain a consistent
state. By default, the greatest extent of lost writes, i.e., those not
made to the journal, are those made in the last 100 milliseconds, plus
the time it takes to perform the actual journal writes. See
commitIntervalMs
for more information on
the default.
Procedures
Disable Journaling
Warning
Do not disable journaling on production systems.
Starting in MongoDB 4.0, you cannot specify
--nojournal
option orstorage.journal.enabled: false
for replica set members that use the WiredTiger storage engine.
To disable journaling for a standalone deployment, start
mongod
with the --nojournal
command line option.
Get Commit Acknowledgement
You can get commit acknowledgement with the Write Concern and
the j
option. For details, see
Write Concern.
Monitor Journal Status
The serverStatus
command/db.serverStatus()
method returns wiredTiger.log
, which contains
statistics on the journal.
Recover Data After Unexpected Shutdown
On a restart after a crash, MongoDB replays all journal files in the
journal directory before the server becomes available. If MongoDB must
replay journal files, mongod
notes these events in the log
output.
There is no reason to run --repair
.
Change WiredTiger Journal Compressor
With the WiredTiger storage engine, MongoDB, by default, uses the
snappy
compressor for the journal. To specify a different
compressions algorithm or no compression for a mongod
instance:
Tip
If you encounter an unclean shutdown for a mongod
during this procedure, you must use the old compressor settings to
recover using the journal files. Once recovered, you can retry the
procedure.
Use the following procedure to change the journal compressor
for a standalone mongod
instance:
Update the
storage.wiredTiger.engineConfig.journalCompressor
setting to the new value.If you use command-line options instead of a configuration file, you will have to update the
--wiredTigerJournalCompressor
command-line option during the restart below.Perform a clean shutdown of the
mongod
instance. For example, connect amongo
shell to the instance and issuedb.shutdownServer()
:db.getSiblingDB('admin').shutdownServer() Once you have confirmed that the process is no longer running, restart the
mongod
instance:If you are using a configuration file:
mongod -f <path/to/myconfig.conf> If you are using command-line options instead of a configuration file, update the
--wiredTigerJournalCompressor
option.mongod --wiredTigerJournalCompressor <differentCompressor|none> ...
Use the following procedure to change the journal compressor for a member of a replica set:
Note
The following procedure involves restarting the replica member as a standalone without the journal.
Perform a clean shutdown of the
mongod
instance. For example, connect amongo
shell to the instance and issuedb.shutdownServer()
:db.getSiblingDB('admin').shutdownServer() Update the configuration file to prepare to restart as a standalone:
Set
storage.journal.enabled
tofalse
.Comment out the replication settings for your deployment.
Set parameter
disableLogicalSessionCacheRefresh
totrue
in thesetParameter
section.
For example:
storage: journal: enabled: false #replication: # replSetName: replA setParameter: disableLogicalSessionCacheRefresh: true If you use command-line options instead of a configuration file, you will have to update the command-line option during the restart.
Restart the
mongod
instance:If you are using a configuration file:
mongod -f <path/to/myconfig.conf> If you are using command-line options instead of a configuration file,
Include the
--nojournal
optionRemove any replication command-line options (such as
--replSet
):Set parameter
disableLogicalSessionCacheRefresh
totrue
in the--setParameter
option.mongod --nojournal --setParameter disableLogicalSessionCacheRefresh=true ...
Perform a clean shutdown of the
mongod
instance:db.getSiblingDB('admin').shutdownServer() Confirm that the process is no longer running.
Update the configuration file to prepare to restart as a replica set member with the new journal compressor:
Remove the
storage.journal.enabled
setting.Uncomment the replication settings for your deployment.
Remove the
disableLogicalSessionCacheRefresh
parameter.Remove
storage.wiredTiger.engineConfig.journalCompressor
setting to use the default journal compressor or specify a new value.
For example:
storage: wiredTiger: engineConfig: journalCompressor: <newValue> replication: replSetName: replA If you use command-line options instead of a configuration file, you will have to update the command-line options during the restart below.
Restart the
mongod
instance as a replica set member:If you are using a configuration file:
mongod -f <path/to/myconfig.conf> If you are using command-line options instead of a configuration file:
Remove the
--nojournal
option.Remove the
--wiredTigerJournalCompressor
command-line option to use the default journal compressor or update to a new value.Include your replication command-line options as well as any additional options for your replica set member.
Remove the
disableLogicalSessionCacheRefresh
parameter.
mongod --wiredTigerJournalCompressor <differentCompressor|none> --replSet ...
Use the following procedure to change the journal compressor for a member of a shard replica set or config server replica set:
Note
The following procedure involves restarting the replica member as a standalone without the journal.
Perform a clean shutdown of the
mongod
instance. For example, connect amongo
shell to the instance and issuedb.shutdownServer()
:db.getSiblingDB('admin').shutdownServer() Update the configuration file to prepare to restart as a standalone:
Set
storage.journal.enabled
tofalse
.Set parameter
skipShardingConfigurationChecks
to true.Set parameter
disableLogicalSessionCacheRefresh
totrue
in thesetParameter
section.Comment out the replication settings for your deployment.
Comment out the
sharding.clusterRole
setting.Set the
net.port
to the member's current port, if it is not explicitly set.
For example:
storage: journal: enabled: false setParameter: skipShardingConfigurationChecks: true disableLogicalSessionCacheRefresh: true #replication: # replSetName: shardA #sharding: # clusterRole: shardsvr net: port: 27218 If you use command-line options instead of a configuration file, you will have to update the command-line option during the restart.
Restart the
mongod
instance:If you are using a configuration file:
mongod -f <path/to/myconfig.conf> If you are using command-line options instead of a configuration file:
Include the
--nojournal
option.Set parameter
skipShardingConfigurationChecks
to true.Set parameter
disableLogicalSessionCacheRefresh
totrue
in the--setParameter
option.Remove any replication command-line options (such as
--replSet
).Remove
--shardsvr
/--configsvr
option.Explicitly include
--port
set to the instance's current port.
mongod --nojournal --setParameter skipShardingConfigurationChecks=true --setParameter disableLogicalSessionCacheRefresh=true --port <samePort> ...
Perform a clean shutdown of the
mongod
instance:db.getSiblingDB('admin').shutdownServer() Confirm that the process is no longer running.
Update the configuration file to prepare to restart with the new journal compressor:
Remove the
storage.journal.enabled
setting.Remove the
skipShardingConfigurationChecks
parameter setting.Remove the
disableLogicalSessionCacheRefresh
parameter setting.Uncomment the replication settings for your deployment.
Uncomment the
sharding.clusterRole
setting.Remove
storage.wiredTiger.engineConfig.journalCompressor
setting to use the default journal compressor or specify a new value.
For example:
storage: wiredTiger: engineConfig: journalCompressor: <newValue> replication: replSetName: shardA sharding: clusterRole: shardsvr net: port: 27218 If you use command-line options instead of a configuration file, you will have to update the command-line options during the restart below.
Restart the
mongod
instance as a replica set member:If you are using a configuration file:
mongod -f <path/to/myconfig.conf> If you are using command-line options instead of a configuration file:
Remove the
--nojournal
option.Remove the
skipShardingConfigurationChecks
parameter setting.Remove the
disableLogicalSessionCacheRefresh
parameter.Remove the
--wiredTigerJournalCompressor
command-line option to use the default journal compressor or update to a new value.Include
--shardsvr
/--configsvr
option.Include your replication command-line options as well as any additional options for your replica set member.
mongod --shardsvr --wiredTigerJournalCompressor <differentCompressor|none> --replSet ...