Provided by: ctdb_4.3.11+dfsg-0ubuntu0.16.04.34_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.
MaxRedirectCount
Default: 3
If we are not the DMASTER and need to fetch a record across the network we first send the
request to the LMASTER after which the record is passed onto the current DMASTER. If the
DMASTER changes before the request has reached that node, the request will be passed onto
the "next" DMASTER. For very hot records that migrate rapidly across the cluster this can
cause a request to "chase" the record for many hops before it catches up with the record.
this is how many hops we allow trying to chase the DMASTER before we switch back to the
LMASTER again to ask for new directions.
When chasing a record, this is how many hops we will chase the record for before going
back to the LMASTER to ask for new guidance.
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 'ms' how frequently ctdb will send out updates to
remote nodes to inform them that the sequence number is increased.
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.
TraverseTimeout
Default: 20
This setting controls how long we allow a traverse process to run. After this timeout
triggers, the main ctdb daemon will abort the traverse if it has not yet finished.
KeepaliveInterval
Default: 5
How often in seconds should the nodes send keepalives to eachother.
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 thus take KeepaliveInterval*(KeepaliveLimit+1) seconds before
we determine that the node is DISCONNECTED and that we require a recovery. This
limitshould not be set too high since we want a hung node to be detectec, and expunged
from the cluster well before common CIFS timeouts (45-90 seconds) kick in.
RecoverTimeout
Default: 20
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.
RecoverInterval
Default: 1
How frequently in seconds should the recovery daemon perform the consistency checks that
determine if we need to perform a recovery or not.
ElectionTimeout
Default: 3
When electing a new recovery master, this is how many seconds we allow the election to
take before we either deem the election finished or we fail the election and start a new
one.
TakeoverTimeout
Default: 9
This is how many seconds we allow controls to take for IP failover events.
MonitorInterval
Default: 15
How often should ctdb run the event scripts to check for a nodes health.
TickleUpdateInterval
Default: 20
How often will ctdb record and store the "tickle" information used to kickstart stalled
tcp connections after a recovery.
EventScriptTimeout
Default: 20
How long should ctdb let an event script run before aborting it and marking the node
unhealthy.
EventScriptTimeoutCount
Default: 1
How many events in a row needs to timeout before we flag the node UNHEALTHY. This setting
is useful if your scripts can not be written so that they do not hang for benign reasons.
EventScriptUnhealthyOnTimeout
Default: 0
This setting can be be used to make ctdb never become UNHEALTHY if your eventscripts keep
hanging/timing out.
RecoveryGracePeriod
Default: 120
During recoveries, if a node has not caused recovery failures during the last grace
period, 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.
RecoveryBanPeriod
Default: 300
If a node becomes banned causing repetitive recovery failures. The node will eventually
become banned from the cluster. This controls how long the culprit node will be banned
from the cluster before it is allowed to try to join the cluster again. Don't set to
small. A node gets banned for a reason and it is usually due to real problems with the
node.
DatabaseHashSize
Default: 100001
Size of the hash chains for the local store of the tdbs that ctdb manages.
DatabaseMaxDead
Default: 5
How many dead records per hashchain in the TDB database do we allow before the freelist
needs to be processed.
RerecoveryTimeout
Default: 10
Once a recovery has completed, no additional recoveries are permitted until this timeout
has expired.
EnableBans
Default: 1
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. You should
set this to the same value on all nodes to avoid unexpected behaviour.
DeterministicIPs
Default: 0
When enabled, this tunable makes ctdb try to keep public IP addresses locked to specific
nodes as far as possible. This makes it easier for debugging since you can know that as
long as all nodes are healthy public IP X will always be hosted by node Y.
The cost of using deterministic IP address assignment is that it disables part of the
logic where ctdb tries to reduce the number of public IP assignment changes in the
cluster. This tunable may increase the number of IP failover/failbacks that are performed
on the cluster by a small margin.
LCP2PublicIPs
Default: 1
When enabled this switches ctdb to use the LCP2 ip allocation algorithm.
ReclockPingPeriod
Default: x
Obsolete
NoIPFailback
Default: 0
When set to 1, ctdb will not perform failback of IP addresses when a node becomes healthy.
Ctdb WILL perform failover of public IP addresses when a node becomes UNHEALTHY, 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.
DisableIPFailover
Default: 0
When enabled, 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 you enable this tunable, 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 failover to replacement nodes using the 'ctdb moveip'
command.
NoIPTakeover
Default: 0
When set to 1, ctdb will not allow IP addresses to be failed over onto this node. Any IP
addresses that the node currently hosts will remain on the node but no new IP addresses
can be failed over to the node.
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 on a node and that node is
disabled it, any IPs hosted by this node will be released and the node will not takeover
any IPs until it is no longer disabled.
DBRecordCountWarn
Default: 100000
When set to non-zero, ctdb will log a warning when we try to recover a database with 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 when we try to recover a database where a
single record is bigger than this. This will produce a warning if a database record grows
uncontrollably with orphaned sub-records.
DBSizeWarn
Default: 1000000000
When set to non-zero, ctdb will log a warning when we try to recover a database bigger
than this. This will produce a warning if a database grows uncontrollably.
VerboseMemoryNames
Default: 0
This feature consumes additional memory. when used the talloc library will create more
verbose names for all talloc allocated objects.
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.
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.
LogLatencyMs
Default: 0
When set to non-zero, this will make the main daemon log any operation that took longer
than this value, in 'ms', to complete. These include "how long time a lockwait child
process needed", "how long time to write to a persistent database" but also "how long did
it take to get a response to a CALL from a remote node".
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 ms.
RecoveryDropAllIPs
Default: 120
If we have been stuck in recovery, or stopped, or banned, mode for this many seconds we
will force drop all held public addresses.
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.
RepackLimit
Default: 10000
During vacuuming, if the number of freelist records are more than RepackLimit, then
databases are repacked to get rid of the freelist records to avoid fragmentation.
Databases are repacked only if both RepackLimit and VacuumLimit are exceeded.
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.
VacuumFastPathCount
Default: 60
When a record is deleted, it is marked for deletion during vacuuming. Vacuuming process
usually processes this list to purge the records from the database. If the number of
records marked for deletion are more than VacuumFastPathCount, then vacuuming process will
scan the complete database for empty records instead of using the list of records marked
for deletion.
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 application 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.
HopcountMakeSticky
Default: 50
If the database is set to 'STICKY' mode, using the 'ctdb setdbsticky' command, any record
that is seen as very hot and migrating so fast that hopcount surpasses 50 is set to become
a STICKY record for StickyDuration seconds. This means that after each migration the
record will be kept on the node and prevented from being migrated off the node.
This setting allows one to try to identify such records and stop them from migrating
across the cluster so fast. This will improve performance for certain workloads, such as
locking.tdb if many clients are opening/closing the same file concurrently.
StickyDuration
Default: 600
Once a record has been found to be fetch-lock hot and has been flagged to become STICKY,
this is for how long, 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 ms. Any request from other nodes to migrate the record off the node
will be deferred until the pindown timer expires.
StatHistoryInterval
Default: 1
Granularity of the statistics collected in the statistics history.
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.
RecoverPDBBySeqNum
Default: 1
When set to zero, database recovery for persistent databases is record-by-record and
recovery process simply collects the most recent version of every individual record.
When set to non-zero, persistent databases will instead be recovered as a whole db and not
by individual records. The node that contains the highest value stored in the record
"__db_sequence_number__" is selected and the copy of that nodes database is used as the
recovered database.
By default, recovery of persistent databses is done using __db_sequence_number__ record.
FetchCollapse
Default: 1
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 parameter is used to activate a fetch-collapse. A fetch-collapse is when we track
which records we have requests in flight so that we only keep one request in flight from a
certain node, even if multiple smbd processes are attemtping to fetch the record at the
same time. This can improve performance and reduce CPU utilization for certain workloads.
This timeout controls if we should collapse multiple fetch operations of the same record
into a single request and defer all duplicates or not.
Samba3AvoidDeadlocks
Default: 0
Enable code that prevents deadlocks with Samba (only for Samba 3.x).
This should be set to 1 when using Samba version 3.x to enable special code in CTDB to
avoid deadlock with Samba version 3.x. This code is not required for Samba version 4.x and
must not be enabled for Samba 4.x.
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.