Provided by: ctdb_4.7.6+dfsg~ubuntu-0ubuntu2.29_amd64 
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.
The tunable variables are listed alphabetically.
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
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.
DisableIPFailover
Default: 0
When set to non-zero, ctdb will not perform failover or failback. Even if a node fails
while holding public IPs, ctdb will not recover the IPs or assign them to another node.
When this tunable is enabled, ctdb will no longer attempt to recover the cluster by
failing IP addresses over to other nodes. This leads to a service outage until the
administrator has manually performed IP failover to replacement nodes using the 'ctdb
moveip' command.
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
"vaccum 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.
NoIPHostOnAllDisabled
Default: 0
If no nodes are HEALTHY then by default ctdb will happily host public IPs on disabled
(unhealthy or administratively disabled) nodes. This can cause problems, for example if
the underlying cluster filesystem is not mounted. When set to 1 and a node is disabled,
any IPs hosted by this node will be released and the node will not takeover any IPs until
it is no longer disabled.
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. Usually IP addresses hosted on
unhealthy nodes will also remain, if NoIPHostOnAllDisabled is 0. However, if
NoIPHostOnAllDisabled is 1 then IP addresses 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 dameon 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 dameon has not heard a "ping" from the recovery dameon for this many seconds,
the main dameon 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 dameon 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 dameon 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.
Databases are repacked only if both RepackLimit and VacuumLimit are exceeded.
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. Everytime 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.
TDBMutexEnabled
Default: 1
This parameter enables TDB_MUTEX_LOCKING feature on volatile databases if the robust
mutexes are supported. This optimizes the record locking using robust mutexes and is much
more efficient that using posix locks.
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.
VacuumLimit
Default: 5000
During vacuuming, if the number of deleted records are more than VacuumLimit, then
databases are repacked to avoid fragmentation.
Databases are repacked only if both RepackLimit and VacuumLimit are exceeded.
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'.
SEE ALSO
ctdb(1), ctdbd(1), ctdbd.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.