source: vendor/current/ctdb/doc/ctdb-tunables.7.xml

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<refentry id="ctdb-tunables.7">

  <refmeta>
    <refentrytitle>ctdb-tunables</refentrytitle>
    <manvolnum>7</manvolnum>
    <refmiscinfo class="source">ctdb</refmiscinfo>
    <refmiscinfo class="manual">CTDB - clustered TDB database</refmiscinfo>
  </refmeta>

  <refnamediv>
    <refname>ctdb-tunables</refname>
    <refpurpose>CTDB tunable configuration variables</refpurpose>
  </refnamediv>

  <refsect1>
    <title>DESCRIPTION</title>

    <para>
      CTDB's behaviour can be configured by setting run-time tunable
      variables.  This lists and describes all tunables.  See the
      <citerefentry><refentrytitle>ctdb</refentrytitle>
      <manvolnum>1</manvolnum></citerefentry>
      <command>listvars</command>, <command>setvar</command> and
      <command>getvar</command> commands for more details.
    </para>

    <para>
      The tunable variables are listed alphabetically.
    </para>

    <refsect2>
      <title>AllowClientDBAttach</title>
      <para>Default: 1</para>
      <para>
        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'.
      </para>
    </refsect2>

    <refsect2>
      <title>AllowUnhealthyDBRead</title>
      <para>Default: 0</para>
      <para>
        When set to 1, ctdb allows database traverses to read unhealthy
        databases.  By default, ctdb does not allow reading records from
        unhealthy databases.
      </para>
    </refsect2>

    <refsect2>
      <title>ControlTimeout</title>
      <para>Default: 60</para>
      <para>
        This is the default setting for timeout for when sending a
        control message to either the local or a remote ctdb daemon.
      </para>
    </refsect2>

    <refsect2>
      <title>DatabaseHashSize</title>
      <para>Default: 100001</para>
      <para>
        Number of the hash chains for the local store of the tdbs that
        ctdb manages.
      </para>
    </refsect2>

    <refsect2>
      <title>DatabaseMaxDead</title>
      <para>Default: 5</para>
      <para>
        Maximum number of dead records per hash chain for the tdb databses
        managed by ctdb.
      </para>
    </refsect2>

    <refsect2>
      <title>DBRecordCountWarn</title>
      <para>Default: 100000</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>DBRecordSizeWarn</title>
      <para>Default: 10000000</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>DBSizeWarn</title>
      <para>Default: 1000000000</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>DeferredAttachTO</title>
      <para>Default: 120</para>
      <para>
        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.
      </para>
      <para>
        This timeout controls how long we will defer the request from the
        client before timing it out and returning an error to the client.
      </para>
    </refsect2>

    <refsect2>
      <title>DeterministicIPs</title>
      <para>Default: 0</para>
      <para>
        When set to 1, ctdb will 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.
      </para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>DisableIPFailover</title>
      <para>Default: 0</para>
      <para>
        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.
      </para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>ElectionTimeout</title>
      <para>Default: 3</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>EnableBans</title>
      <para>Default: 1</para>
      <para>
        This parameter allows ctdb to ban a node if the node is misbehaving.
      </para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>EventScriptTimeout</title>
      <para>Default: 30</para>
      <para>
        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.
      </para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>FetchCollapse</title>
      <para>Default: 1</para>
      <para>
       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.
      </para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>HopcountMakeSticky</title>
      <para>Default: 50</para>
      <para>
        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
        <varname>StickyDuration</varname> seconds. This means that
        after each migration the sticky record will be kept on the node
        <varname>StickyPindown</varname>milliseconds and prevented from
        being migrated off the node.
       </para>
       <para>
        This will improve performance for certain workloads, such as
        locking.tdb if many clients are opening/closing the same file
        concurrently.
      </para>
    </refsect2>

    <refsect2>
      <title>KeepaliveInterval</title>
      <para>Default: 5</para>
      <para>
        How often in seconds should the nodes send keep-alive packets to
        each other.
      </para>
    </refsect2>

    <refsect2>
      <title>KeepaliveLimit</title>
      <para>Default: 5</para>
      <para>
        After how many keepalive intervals without any traffic should
        a node wait until marking the peer as DISCONNECTED.
       </para>
       <para>
        If a node has hung, it can take
        <varname>KeepaliveInterval</varname> *
        (<varname>KeepaliveLimit</varname> + 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.
      </para>
    </refsect2>

    <refsect2>
      <title>LCP2PublicIPs</title>
      <para>Default: 1</para>
      <para>
        When set to 1, ctdb uses the LCP2 ip allocation algorithm.
      </para>
    </refsect2>

    <refsect2>
      <title>LockProcessesPerDB</title>
      <para>Default: 200</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>LogLatencyMs</title>
      <para>Default: 0</para>
      <para>
        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".
      </para>
    </refsect2>

    <refsect2>
      <title>MaxQueueDropMsg</title>
      <para>Default: 1000000</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>MonitorInterval</title>
      <para>Default: 15</para>
      <para>
        How often should ctdb run the 'monitor' event in seconds to check
        for a node's health.
      </para>
    </refsect2>

    <refsect2>
      <title>MonitorTimeoutCount</title>
      <para>Default: 20</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>NoIPFailback</title>
      <para>Default: 0</para>
      <para>
        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.
      </para>
      <para>
        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.
      </para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>NoIPHostOnAllDisabled</title>
      <para>Default: 0</para>
      <para>
        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, any IPs hosted by this node will be
        released and the node will not takeover any IPs until it is no
        longer disabled.
      </para>
    </refsect2>

    <refsect2>
      <title>NoIPTakeover</title>
      <para>Default: 0</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>PullDBPreallocation</title>
      <para>Default: 10*1024*1024</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>RecBufferSizeLimit</title>
      <para>Default: 1000000</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>RecdFailCount</title>
      <para>Default: 10</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>RecdPingTimeout</title>
      <para>Default: 60</para>
      <para>
        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 <varname>RecdFailCount</varname>
        for detection of hung recovery daemon.
      </para>
    </refsect2>

    <refsect2>
      <title>RecLockLatencyMs</title>
      <para>Default: 1000</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>RecoverInterval</title>
      <para>Default: 1</para>
      <para>
        How frequently in seconds should the recovery daemon perform the
        consistency checks to determine if it should perform a recovery.
      </para>
    </refsect2>

    <refsect2>
      <title>RecoverPDBBySeqNum</title>
      <para>Default: 1</para>
      <para>
        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.
      </para>
      <para>
        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.
      </para>
      <para>
        By default, recovery of persistent databses is done using
        __db_sequence_number__ record.
      </para>
    </refsect2>

    <refsect2>
      <title>RecoverTimeout</title>
      <para>Default: 120</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>RecoveryBanPeriod</title>
      <para>Default: 300</para>
      <para>
       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.
      </para>
      <para>
       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.
      </para>
    </refsect2>

    <refsect2>
      <title>RecoveryDropAllIPs</title>
      <para>Default: 120</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>RecoveryGracePeriod</title>
      <para>Default: 120</para>
      <para>
       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.
      </para>
    </refsect2>

    <refsect2>
      <title>RepackLimit</title>
      <para>Default: 10000</para>
      <para>
        During vacuuming, if the number of freelist records are more than
        <varname>RepackLimit</varname>, then the database is repacked
        to get rid of the freelist records to avoid fragmentation.
      </para>
      <para>
        Databases are repacked only if both <varname>RepackLimit</varname>
        and <varname>VacuumLimit</varname> are exceeded.
      </para>
    </refsect2>

    <refsect2>
      <title>RerecoveryTimeout</title>
      <para>Default: 10</para>
      <para>
        Once a recovery has completed, no additional recoveries are
        permitted until this timeout in seconds has expired.
      </para>
    </refsect2>

    <refsect2>
      <title>Samba3AvoidDeadlocks</title>
      <para>Default: 0</para>
      <para>
        If set to non-zero, enable code that prevents deadlocks with Samba
        (only for Samba 3.x).
      </para> <para>
        This should be set to 1 only 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.
      </para>
    </refsect2>

    <refsect2>
      <title>SeqnumInterval</title>
      <para>Default: 1000</para>
      <para>
        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.
      </para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>StatHistoryInterval</title>
      <para>Default: 1</para>
      <para>
        Granularity of the statistics collected in the statistics
        history. This is reported by 'ctdb stats' command.
      </para>
    </refsect2>

    <refsect2>
      <title>StickyDuration</title>
      <para>Default: 600</para>
      <para>
        Once a record has been marked STICKY, this is the duration in
        seconds, the record will be flagged as a STICKY record.
      </para>
    </refsect2>

    <refsect2>
      <title>StickyPindown</title>
      <para>Default: 200</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>TakeoverTimeout</title>
      <para>Default: 9</para>
      <para>
        This is the duration in seconds in which ctdb tries to complete IP
        failover.
      </para>
    </refsect2>

    <refsect2>
      <title>TDBMutexEnabled</title>
      <para>Default: 0</para>
      <para>
        This paramter 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.
      </para>
    </refsect2>

    <refsect2>
      <title>TickleUpdateInterval</title>
      <para>Default: 20</para>
      <para>
        Every <varname>TickleUpdateInterval</varname> seconds, ctdb
        synchronizes the client connection information across nodes.
      </para>
    </refsect2>

    <refsect2>
      <title>TraverseTimeout</title>
      <para>Default: 20</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>VacuumFastPathCount</title>
      <para>Default: 60</para>
      <para>
       During a vacuuming run, ctdb usually processes only the records
       marked for deletion also called the fast path vacuuming. After
       finishing <varname>VacuumFastPathCount</varname> number of fast
       path vacuuming runs, ctdb will trigger a scan of complete database
       for any empty records that need to be deleted.
      </para>
    </refsect2>

    <refsect2>
      <title>VacuumInterval</title>
      <para>Default: 10</para>
      <para>
        Periodic interval in seconds when vacuuming is triggered for
        volatile databases.
      </para>
    </refsect2>

    <refsect2>
      <title>VacuumLimit</title>
      <para>Default: 5000</para>
      <para>
        During vacuuming, if the number of deleted records are more than
        <varname>VacuumLimit</varname>, then databases are repacked to
        avoid fragmentation.
      </para>
      <para>
        Databases are repacked only if both <varname>RepackLimit</varname>
        and <varname>VacuumLimit</varname> are exceeded.
      </para>
    </refsect2>

    <refsect2>
      <title>VacuumMaxRunTime</title>
      <para>Default: 120</para>
      <para>
        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.
      </para>
    </refsect2>

    <refsect2>
      <title>VerboseMemoryNames</title>
      <para>Default: 0</para>
      <para>
        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'.
      </para>
    </refsect2>

  </refsect1>

  <refsect1>
    <title>SEE ALSO</title>
    <para>
      <citerefentry><refentrytitle>ctdb</refentrytitle>
      <manvolnum>1</manvolnum></citerefentry>,

      <citerefentry><refentrytitle>ctdbd</refentrytitle>
      <manvolnum>1</manvolnum></citerefentry>,

      <citerefentry><refentrytitle>ctdbd.conf</refentrytitle>
      <manvolnum>5</manvolnum></citerefentry>,

      <citerefentry><refentrytitle>ctdb</refentrytitle>
      <manvolnum>7</manvolnum></citerefentry>,

      <ulink url="http://ctdb.samba.org/"/>
    </para>
  </refsect1>

  <refentryinfo>
    <author>
      <contrib>
        This documentation was written by
        Ronnie Sahlberg,
        Amitay Isaacs,
        Martin Schwenke
      </contrib>
    </author>

    <copyright>
      <year>2007</year>
      <holder>Andrew Tridgell</holder>
      <holder>Ronnie Sahlberg</holder>
    </copyright>
    <legalnotice>
      <para>
        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.
      </para>
      <para>
        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.
      </para>
      <para>
        You should have received a copy of the GNU General Public
        License along with this program; if not, see
        <ulink url="http://www.gnu.org/licenses"/>.
      </para>
    </legalnotice>
  </refentryinfo>

</refentry>