NAME

       ctdb-tunables - CTDB tunable configuration variables

DESCRIPTION

       CTDB's behaviour can be configured by setting run-time tunable variables. This lists and
       describes all tunables. See the ctdb(1) listvars, setvar and getvar commands for more
       details.

       Unless otherwise stated, tunables should be set to the same value on all nodes. Setting
       tunables to different values across nodes may produce unexpected results. Future releases
       may set (some or most) tunables globally across the cluster but doing so is currently a
       manual process.

       Tunables can be set at startup from the /etc/ctdb/ctdb.tunables configuration file.

           TUNABLE=VALUE

       For example:

           MonitorInterval=20

       The available tunable variables are listed alphabetically below.

   AllowClientDBAttach
       Default: 1

       When set to 0, clients are not allowed to attach to any databases. This can be used to
       temporarily block any new processes from attaching to and accessing the databases. This is
       mainly used for detaching a volatile database using 'ctdb detach'.

   AllowMixedVersions
       Default: 0

       CTDB will not allow incompatible versions to co-exist in a cluster. If a version mismatch
       is found, then losing CTDB will shutdown. To disable the incompatible version check, set
       this tunable to 1.

       For version checking, CTDB uses major and minor version. For example, CTDB 4.6.1 and CTDB
       4.6.2 are matching versions; CTDB 4.5.x and CTDB 4.6.y do not match.

       CTDB with version check support will lose to CTDB without version check support. Between
       two different CTDB versions with version check support, one running for less time will
       lose. If the running time for both CTDB versions with version check support is equal (to
       seconds), then the older version will lose. The losing CTDB daemon will shutdown.

   AllowUnhealthyDBRead
       Default: 0

       When set to 1, ctdb allows database traverses to read unhealthy databases. By default,
       ctdb does not allow reading records from unhealthy databases.

   ControlTimeout
       Default: 60

       This is the default setting for timeout for when sending a control message to either the
       local or a remote ctdb daemon.

   DatabaseHashSize
       Default: 100001

       Number of the hash chains for the local store of the tdbs that ctdb manages.

   DatabaseMaxDead
       Default: 5

       Maximum number of dead records per hash chain for the tdb databses managed by ctdb.

   DBRecordCountWarn
       Default: 100000

       When set to non-zero, ctdb will log a warning during recovery if a database has more than
       this many records. This will produce a warning if a database grows uncontrollably with
       orphaned records.

   DBRecordSizeWarn
       Default: 10000000

       When set to non-zero, ctdb will log a warning during recovery if a single record is bigger
       than this size. This will produce a warning if a database record grows uncontrollably.

   DBSizeWarn
       Default: 1000000000

       When set to non-zero, ctdb will log a warning during recovery if a database size is bigger
       than this. This will produce a warning if a database grows uncontrollably.

   DeferredAttachTO
       Default: 120

       When databases are frozen we do not allow clients to attach to the databases. Instead of
       returning an error immediately to the client, the attach request from the client is
       deferred until the database becomes available again at which stage we respond to the
       client.

       This timeout controls how long we will defer the request from the client before timing it
       out and returning an error to the client.

   ElectionTimeout
       Default: 3

       The number of seconds to wait for the election of recovery master to complete. If the
       election is not completed during this interval, then that round of election fails and ctdb
       starts a new election.

   EnableBans
       Default: 1

       This parameter allows ctdb to ban a node if the node is misbehaving.

       When set to 0, this disables banning completely in the cluster and thus nodes can not get
       banned, even it they break. Don't set to 0 unless you know what you are doing.

   EventScriptTimeout
       Default: 30

       Maximum time in seconds to allow an event to run before timing out. This is the total time
       for all enabled scripts that are run for an event, not just a single event script.

       Note that timeouts are ignored for some events ("takeip", "releaseip", "startrecovery",
       "recovered") and converted to success. The logic here is that the callers of these events
       implement their own additional timeout.

   FetchCollapse
       Default: 1

       This parameter is used to avoid multiple migration requests for the same record from a
       single node. All the record requests for the same record are queued up and processed when
       the record is migrated to the current node.

       When many clients across many nodes try to access the same record at the same time this
       can lead to a fetch storm where the record becomes very active and bounces between nodes
       very fast. This leads to high CPU utilization of the ctdbd daemon, trying to bounce that
       record around very fast, and poor performance. This can improve performance and reduce CPU
       utilization for certain workloads.

   HopcountMakeSticky
       Default: 50

       For database(s) marked STICKY (using 'ctdb setdbsticky'), any record that is migrating so
       fast that hopcount exceeds this limit is marked as STICKY record for StickyDuration
       seconds. This means that after each migration the sticky record will be kept on the node
       StickyPindownmilliseconds and prevented from being migrated off the node.

       This will improve performance for certain workloads, such as locking.tdb if many clients
       are opening/closing the same file concurrently.

   IPAllocAlgorithm
       Default: 2

       Selects the algorithm that CTDB should use when doing public IP address allocation.
       Meaningful values are:

       0
           Deterministic IP address allocation.

           This is a simple and fast option. However, it can cause unnecessary address movement
           during fail-over because each address has a "home" node. Works badly when some nodes
           do not have any addresses defined. Should be used with care when addresses are defined
           across multiple networks.

       1
           Non-deterministic IP address allocation.

           This is a relatively fast option that attempts to do a minimise unnecessary address
           movements. Addresses do not have a "home" node. Rebalancing is limited but it usually
           adequate. Works badly when addresses are defined across multiple networks.

       2
           LCP2 IP address allocation.

           Uses a heuristic to assign addresses defined across multiple networks, usually
           balancing addresses on each network evenly across nodes. Addresses do not have a
           "home" node. Minimises unnecessary address movements. The algorithm is complex, so is
           slower than other choices for a large number of addresses. However, it can calculate
           an optimal assignment of 900 addresses in under 10 seconds on modern hardware.

       If the specified value is not one of these then the default will be used.

   KeepaliveInterval
       Default: 5

       How often in seconds should the nodes send keep-alive packets to each other.

   KeepaliveLimit
       Default: 5

       After how many keepalive intervals without any traffic should a node wait until marking
       the peer as DISCONNECTED.

       If a node has hung, it can take KeepaliveInterval * (KeepaliveLimit + 1) seconds before
       ctdb determines that the node is DISCONNECTED and performs a recovery. This limit should
       not be set too high to enable early detection and avoid any application timeouts (e.g.
       SMB1) to kick in before the fail over is completed.

   LockProcessesPerDB
       Default: 200

       This is the maximum number of lock helper processes ctdb will create for obtaining record
       locks. When ctdb cannot get a record lock without blocking, it creates a helper process
       that waits for the lock to be obtained.

   LogLatencyMs
       Default: 0

       When set to non-zero, ctdb will log if certains operations take longer than this value, in
       milliseconds, to complete. These operations include "process a record request from
       client", "take a record or database lock", "update a persistent database record" and
       "vacuum a database".

   MaxQueueDropMsg
       Default: 1000000

       This is the maximum number of messages to be queued up for a client before ctdb will treat
       the client as hung and will terminate the client connection.

   MonitorInterval
       Default: 15

       How often should ctdb run the 'monitor' event in seconds to check for a node's health.

   MonitorTimeoutCount
       Default: 20

       How many 'monitor' events in a row need to timeout before a node is flagged as UNHEALTHY.
       This setting is useful if scripts can not be written so that they do not hang for benign
       reasons.

   NoIPFailback
       Default: 0

       When set to 1, ctdb will not perform failback of IP addresses when a node becomes healthy.
       When a node becomes UNHEALTHY, ctdb WILL perform failover of public IP addresses, but when
       the node becomes HEALTHY again, ctdb will not fail the addresses back.

       Use with caution! Normally when a node becomes available to the cluster ctdb will try to
       reassign public IP addresses onto the new node as a way to distribute the workload evenly
       across the clusternode. Ctdb tries to make sure that all running nodes have approximately
       the same number of public addresses it hosts.

       When you enable this tunable, ctdb will no longer attempt to rebalance the cluster by
       failing IP addresses back to the new nodes. An unbalanced cluster will therefore remain
       unbalanced until there is manual intervention from the administrator. When this parameter
       is set, you can manually fail public IP addresses over to the new node(s) using the 'ctdb
       moveip' command.

   NoIPTakeover
       Default: 0

       When set to 1, ctdb will not allow IP addresses to be failed over to other nodes. Any IP
       addresses already hosted on healthy nodes will remain. Any IP addresses hosted on
       unhealthy nodes will be released by unhealthy nodes and will become un-hosted.

   PullDBPreallocation
       Default: 10*1024*1024

       This is the size of a record buffer to pre-allocate for sending reply to PULLDB control.
       Usually record buffer starts with size of the first record and gets reallocated every time
       a new record is added to the record buffer. For a large number of records, this can be
       very inefficient to grow the record buffer one record at a time.

   QueueBufferSize
       Default: 1024

       This is the maximum amount of data (in bytes) ctdb will read from a socket at a time.

       For a busy setup, if ctdb is not able to process the TCP sockets fast enough (large amount
       of data in Recv-Q for tcp sockets), then this tunable value should be increased. However,
       large values can keep ctdb busy processing packets and prevent ctdb from handling other
       events.

   RecBufferSizeLimit
       Default: 1000000

       This is the limit on the size of the record buffer to be sent in various controls. This
       limit is used by new controls used for recovery and controls used in vacuuming.

   RecdFailCount
       Default: 10

       If the recovery daemon has failed to ping the main daemon for this many consecutive
       intervals, the main daemon will consider the recovery daemon as hung and will try to
       restart it to recover.

   RecdPingTimeout
       Default: 60

       If the main daemon has not heard a "ping" from the recovery daemon for this many seconds,
       the main daemon will log a message that the recovery daemon is potentially hung. This also
       increments a counter which is checked against RecdFailCount for detection of hung recovery
       daemon.

   RecLockLatencyMs
       Default: 1000

       When using a reclock file for split brain prevention, if set to non-zero this tunable will
       make the recovery daemon log a message if the fcntl() call to lock/testlock the recovery
       file takes longer than this number of milliseconds.

   RecoverInterval
       Default: 1

       How frequently in seconds should the recovery daemon perform the consistency checks to
       determine if it should perform a recovery.

   RecoverTimeout
       Default: 120

       This is the default setting for timeouts for controls when sent from the recovery daemon.
       We allow longer control timeouts from the recovery daemon than from normal use since the
       recovery daemon often use controls that can take a lot longer than normal controls.

   RecoveryBanPeriod
       Default: 300

       The duration in seconds for which a node is banned if the node fails during recovery.
       After this time has elapsed the node will automatically get unbanned and will attempt to
       rejoin the cluster.

       A node usually gets banned due to real problems with the node. Don't set this value too
       small. Otherwise, a problematic node will try to re-join cluster too soon causing
       unnecessary recoveries.

   RecoveryDropAllIPs
       Default: 120

       If a node is stuck in recovery, or stopped, or banned, for this many seconds, then ctdb
       will release all public addresses on that node.

   RecoveryGracePeriod
       Default: 120

       During recoveries, if a node has not caused recovery failures during the last grace period
       in seconds, any records of transgressions that the node has caused recovery failures will
       be forgiven. This resets the ban-counter back to zero for that node.

   RepackLimit
       Default: 10000

       During vacuuming, if the number of freelist records are more than RepackLimit, then the
       database is repacked to get rid of the freelist records to avoid fragmentation.

   RerecoveryTimeout
       Default: 10

       Once a recovery has completed, no additional recoveries are permitted until this timeout
       in seconds has expired.

   SeqnumInterval
       Default: 1000

       Some databases have seqnum tracking enabled, so that samba will be able to detect
       asynchronously when there has been updates to the database. Every time a database is
       updated its sequence number is increased.

       This tunable is used to specify in milliseconds how frequently ctdb will send out updates
       to remote nodes to inform them that the sequence number is increased.

   StatHistoryInterval
       Default: 1

       Granularity of the statistics collected in the statistics history. This is reported by
       'ctdb stats' command.

   StickyDuration
       Default: 600

       Once a record has been marked STICKY, this is the duration in seconds, the record will be
       flagged as a STICKY record.

   StickyPindown
       Default: 200

       Once a STICKY record has been migrated onto a node, it will be pinned down on that node
       for this number of milliseconds. Any request from other nodes to migrate the record off
       the node will be deferred.

   TakeoverTimeout
       Default: 9

       This is the duration in seconds in which ctdb tries to complete IP failover.

   TickleUpdateInterval
       Default: 20

       Every TickleUpdateInterval seconds, ctdb synchronizes the client connection information
       across nodes.

   TraverseTimeout
       Default: 20

       This is the duration in seconds for which a database traverse is allowed to run. If the
       traverse does not complete during this interval, ctdb will abort the traverse.

   VacuumFastPathCount
       Default: 60

       During a vacuuming run, ctdb usually processes only the records marked for deletion also
       called the fast path vacuuming. After finishing VacuumFastPathCount number of fast path
       vacuuming runs, ctdb will trigger a scan of complete database for any empty records that
       need to be deleted.

   VacuumInterval
       Default: 10

       Periodic interval in seconds when vacuuming is triggered for volatile databases.

   VacuumMaxRunTime
       Default: 120

       The maximum time in seconds for which the vacuuming process is allowed to run. If
       vacuuming process takes longer than this value, then the vacuuming process is terminated.

   VerboseMemoryNames
       Default: 0

       When set to non-zero, ctdb assigns verbose names for some of the talloc allocated memory
       objects. These names are visible in the talloc memory report generated by 'ctdb
       dumpmemory'.

FILES>

           /etc/ctdb/ctdb.tunables

SEE ALSO

       ctdb(1), ctdbd(1), ctdb.conf(5), ctdb(7), http://ctdb.samba.org/

AUTHOR

       This documentation was written by Ronnie Sahlberg, Amitay Isaacs, Martin Schwenke

COPYRIGHT

       Copyright © 2007 Andrew Tridgell, Ronnie Sahlberg

       This program is free software; you can redistribute it and/or modify it under the terms of
       the GNU General Public License as published by the Free Software Foundation; either
       version 3 of the License, or (at your option) any later version.

       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
       without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
       See the GNU General Public License for more details.

       You should have received a copy of the GNU General Public License along with this program;
       if not, see http://www.gnu.org/licenses.