Merge lp:~hrvojem/percona-xtradb-cluster/bug1319708-5.6 into lp:percona-xtradb-cluster

[Hrvoje Matijakovic]

[Raghavendra D Prabhu (raghavendra-prabhu)]

In-line comments added.

review: Needs Fixing

[Raghavendra D Prabhu (raghavendra-prabhu)]

lp:1280896 and lp:1260713 are two important bugs to be added as they are fixed.

lp:1260713 specifically introduces two new variables - wsrep_slave_FK_checks and wsrep_slave_UK_checks which are set to TRUE and FALSE respectively by default. They control whether FK and UK checking is done for applier threads.

[Raghavendra D Prabhu (raghavendra-prabhu)]

Noted in in-line diff comments. Also, note that new variables added will need to be documented under variables.

review: Needs Fixing

[Raghavendra D Prabhu (raghavendra-prabhu)]

Added inline diff comments.

review: Needs Fixing

[Raghavendra D Prabhu (raghavendra-prabhu)]

Looks good.

review: Approve

[lp:~hrvojem/percona-xtradb-cluster/bug1319708-5.6]

777. By Hrvoje Matijakovic on 2014-07-18

- Bug fix for Bug #1319708
- Percona-XtraDB-Cluster-5.6.19-25.6 release notes

=== modified file '.bzrignore'
--- .bzrignore	2014-07-02 10:52:20 +0000
+++ .bzrignore	2014-07-18 11:34:40 +0000
@@ -3147,3 +3147,4 @@
 storage/perfschema/gen_pfs_lex_token
 sql/share/bulgarian
 doc/build
+doc-pxc/build/
 
=== modified file 'doc-pxc/source/conf.py'
--- doc-pxc/source/conf.py	2014-03-20 09:43:39 +0000
+++ doc-pxc/source/conf.py	2014-07-18 11:34:40 +0000
@@ -53,9 +53,9 @@
 # built documents.
 #
 # The short X.Y version.
-version = '5.6.15'
+version = '5.6.19'
 # The full version, including alpha/beta/rc tags.
-release = '5.6.15-25.5'
+release = '5.6.19-25.6'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
@@ -136,8 +136,6 @@
 
 .. |Drizzle|  replace:: *Drizzle*
 
-.. |MariaDB|  replace:: *MariaDB*
-
 .. |tar4ibd|  replace:: :program:`tar4ibd`
 
 .. |tar|  replace:: :program:`tar`
@@ -146,6 +144,7 @@
 
 extlinks = {'bug': ('https://bugs.launchpad.net/percona-xtradb-cluster/+bug/%s',
                       '#'), 'mysqlbug': ('http://bugs.mysql.com/bug.php?id=%s',
+                      '#'), 'githubbug': ('https://github.com/codership/galera/issues/%s',
                       '#')}
 
 # A list of ignored prefixes for module index sorting.
 
=== modified file 'doc-pxc/source/glossary.rst'
--- doc-pxc/source/glossary.rst	2013-09-05 13:37:01 +0000
+++ doc-pxc/source/glossary.rst	2014-07-18 11:34:40 +0000
@@ -32,7 +32,7 @@
      *Percona XtraBackup* is an open-source hot backup utility for |MySQL| - based servers that doesn’t lock your database during the backup.
 
    XtraDB
-     *Percona XtraDB* is an enhanced version of the InnoDB storage engine, designed to better scale on modern hardware, and including a variety of other features useful in high performance environments. It is fully backwards compatible, and so can be used as a drop-in replacement for standard InnoDB. More information `here <http://www.percona.com/docs/wiki/Percona-XtraDB:start>`_ .
+     *Percona XtraDB* is an enhanced version of the InnoDB storage engine, designed to better scale on modern hardware, and including a variety of other features useful in high performance environments. It is fully backwards compatible, and so can be used as a drop-in replacement for standard InnoDB. More information `here <http://www.percona.com/doc/percona-server/5.5/percona_xtradb.html>`_ .
 
    XtraDB Cluster
      *Percona XtraDB Cluster* is a high availability solution for MySQL.
 
=== modified file 'doc-pxc/source/howtos/virt_sandbox.rst'
--- doc-pxc/source/howtos/virt_sandbox.rst	2013-09-05 13:37:01 +0000
+++ doc-pxc/source/howtos/virt_sandbox.rst	2014-07-18 11:34:40 +0000
@@ -7,7 +7,7 @@
 
 The client node will have HAProxy installed and it will redirect requests to |PXC| nodes. This approach works well in real-world scenarios too. Running HAProxy on the application servers instead of having them as dedicated entities gives you benefits like no need for an extra network roundtrip, because loadbalancer and scalability of |PXC|'s load balancing layer scales simply with application servers.
 
-We'll use `Percona <http://www.percona.com/docs/wiki/repositories:yum>`_ and `EPEL <http://fedoraproject.org/wiki/EPEL>`_ repositories for software installation.
+We'll use `Percona <http://www.percona.com/doc/percona-xtradb-cluster/5.6/installation/yum_repo.html>`_ and `EPEL <http://fedoraproject.org/wiki/EPEL>`_ repositories for software installation.
 
 After configuring the repositories you'll be able to install software that will be used. First, install |PXC| on the database nodes. ::
 
 
=== modified file 'doc-pxc/source/installation/apt_repo.rst'
--- doc-pxc/source/installation/apt_repo.rst	2014-01-29 15:10:12 +0000
+++ doc-pxc/source/installation/apt_repo.rst	2014-07-18 11:34:40 +0000
@@ -37,13 +37,12 @@
 
  * 10.04LTS lucid
  * 12.04LTS precise
- * 12.10 quantal
- * 13.04 raring
  * 13.10 saucy
-
-
-Install XtraDB Cluster
-=======================
+ * 14.04LTS trusty
+
+
+Install Percona XtraDB Cluster
+==============================
 
 Make sure to remove existing |Percona XtraDB Cluster| 5.5 and |Percona Server| 5.5/5.6 packages before proceeding.
 
@@ -64,3 +63,15 @@
 
   deb http://repo.percona.com/apt VERSION main experimental
   deb-src http://repo.percona.com/apt VERSION main experimental
+
+Apt-Pinning the packages
+========================
+
+In some cases you might need to "pin" the selected packages to avoid the upgrades from the distribution repositories. You'll need to make a new file :file:`/etc/apt/preferences.d/00percona.pref` and add the following lines in it: :: 
+
+  Package: *
+  Pin: release o=Percona Development Team
+  Pin-Priority: 1001
+
+For more information about the pinning you can check the official `debian wiki <http://wiki.debian.org/AptPreferences>`_.
+
 
=== modified file 'doc-pxc/source/intro.rst'
--- doc-pxc/source/intro.rst	2014-03-20 09:43:39 +0000
+++ doc-pxc/source/intro.rst	2014-07-18 11:34:40 +0000
@@ -54,7 +54,7 @@
 It uses  the  `Galera library <https://launchpad.net/galera>`_, version 3.x, 
 a generic Synchronous Multi-Master replication plugin for transactional applications. 
 
-Galera library is developed by `Codership Oy <http://www.codership.com/>`_.
+Galera library is developed by `Codership Oy <http://www.galeracluster.com/>`_.
 
 Galera 3.x supports such new features as:
  * Incremental State Transfer (|IST|), especially useful for WAN deployments,
 
=== modified file 'doc-pxc/source/manual/state_snapshot_transfer.rst'
--- doc-pxc/source/manual/state_snapshot_transfer.rst	2014-01-30 13:56:19 +0000
+++ doc-pxc/source/manual/state_snapshot_transfer.rst	2014-07-18 11:34:40 +0000
@@ -39,5 +39,5 @@
 Other Reading
 =============
 
-* `SST Methods for MySQL <http://www.codership.com/wiki/doku.php?id=sst_mysql>`_
+* `SST Methods for MySQL <http://galeracluster.com/documentation-webpages/statetransfer.html#state-snapshot-transfer-sst>`_
 * :ref:`Xtrabackup SST configuration<xtrabackup_sst>`
 
=== modified file 'doc-pxc/source/manual/xtrabackup_sst.rst'
--- doc-pxc/source/manual/xtrabackup_sst.rst	2014-03-20 13:08:06 +0000
+++ doc-pxc/source/manual/xtrabackup_sst.rst	2014-07-18 11:34:40 +0000
@@ -79,7 +79,7 @@
 
   * OpenSSL based encryption with ``encrypt=2``. Socat must be built with openSSL for encryption: ``socat -V | grep OPENSSL``.
 
-  * Support for SSL encryption for just the key and crt files as implemented in `Galera <http://www.codership.com/wiki/doku.php?id=ssl_support>`_ can be enabled with ``encrypt=3`` option. Information on this option can be found :ref:`here <galera_sst_encryption>`.
+  * Support for SSL encryption for just the key and crt files as implemented in `Galera <http://galeracluster.com/documentation-webpages/ssl.html?highlight=ssl#enabling-ssl>`_ can be enabled with ``encrypt=3`` option. Information on this option can be found :ref:`here <galera_sst_encryption>`.
 
 Refer to this :ref:`document <xtrabackup_sst_encryption>` when enabling with ``encrypt=1``.
 
@@ -215,7 +215,7 @@
 Galera compatible encryption
 ----------------------------
 
-Support for SSL encryption for just the key and crt files as implemented in `Galera <http://www.codership.com/wiki/doku.php?id=ssl_support>`_ can be enabled with ``encrypt=3`` option. This has been implemented in :rn:`5.5.34-23.7.6` for compatibility with Galera. **NOTE**: This option does not provide certificate validation. In order to work correctly paths to the key and cert files need to be specified as well, like: ::
+Support for SSL encryption for just the key and crt files as implemented in `Galera <http://galeracluster.com/documentation-webpages/ssl.html?highlight=ssl#enabling-ssl>`_ can be enabled with ``encrypt=3`` option. This has been implemented in :rn:`5.5.34-23.7.6` for compatibility with Galera. **NOTE**: This option does not provide certificate validation. In order to work correctly paths to the key and cert files need to be specified as well, like: ::
 
    [sst] 
    encrypt=3
 
=== added file 'doc-pxc/source/release-notes/Percona-XtraDB-Cluster-5.6.19-25.6.rst'
--- doc-pxc/source/release-notes/Percona-XtraDB-Cluster-5.6.19-25.6.rst	1970-01-01 00:00:00 +0000
+++ doc-pxc/source/release-notes/Percona-XtraDB-Cluster-5.6.19-25.6.rst	2014-07-18 11:34:40 +0000
@@ -0,0 +1,106 @@
+.. rn:: 5.6.17-25.6
+
+======================================
+ |Percona XtraDB Cluster| 5.6.19-25.6 
+======================================
+
+Percona is glad to announce the release of |Percona XtraDB Cluster| 5.6 on July 21st 2014. Binaries are available from `downloads area <http://www.percona.com/downloads/Percona-XtraDB-Cluster-56/release-5.6.19-25.6/>`_ or from our :doc:`software repositories </installation>`.
+
+Based on `Percona Server 5.6.19-67.0 <http://www.percona.com/doc/percona-server/5.6/release-notes/Percona-Server-5.6.19-67.0.html>`_ including all the bug fixes in it, `Galera Replicator 3.6 <https://github.com/codership/galera/issues?milestone=1&page=1&state=closed>`_ and on `Codership wsrep API 25.6 <https://launchpad.net/wsrep-group/+milestone/5.6.19-25.6>`_ is now the current **General Availability** release. All of |Percona|'s software is open-source and free, all the details of the release can be found in the `5.6.19-25.6 milestone <https://launchpad.net/percona-xtradb-cluster/+milestone/5.6.19-25.6>`_ at Launchpad.
+
+New Features
+============
+ 
+ During joiner joining the group, state message exchange provides us with ``gcache seqno limits``. That info is now used to choose a donor through IST first, if not possible, only then SST is attempted. :variable:`wsrep_sst_donor` is also honored here. This is also segment aware. (:bug:`1252461`)
+
+ Asynchronous replication slave thread is stopped when the node tries to apply next replication event while the node is in non-primary state. But it would then remain stopped after node successfully re-joined the cluster. A new variable :variable:`wsrep_restart_slave` has been implemented, which controls if |MySQL| slave should be restarted automatically when the node joins back to the cluster. (:bug:`1288479`)
+
+ Handling install message and install state message processing has been improved to make group forming more stable in case many nodes are joining the cluster. (:githubbug:`14`)
+
+ |Percona XtraDB Cluster| now supports storing the Primary Component state to disk by setting the :variable:`pc.recovery` variable to ``true``. The Primary Component can then recover automatically when all nodes that were part of the last saved state reestablish communications with each other. This feature can be used for automatic recovery from full cluster crashes, such as in the case of a data center power outage and graceful full cluster restarts without the need for explicitly bootstrapping a new Primary Component. (:githubbug:`10`)
+
+ New :variable:`wsrep_evs_repl_latency` status variable has been implemented which provides the group communication replication latency information. (:githubbug:`15`)
+
+ Node consistency issues with foreign keys have been fixed. This fix introduces two new variables: :variable:`wsrep_slave_FK_checks` and :variable:`wsrep_slave_UK_checks`. These variables are set to ``TRUE`` and ``FALSE`` respectively by default. They control whether Foreign Key and Unique Key checking is done for applier threads. (:bug:`1260713`).
+
+Bugs fixed 
+==========
+
+ Fixed the race condition in Foreign Key processing that could cause assertion. Bug fixed :bug:`1342959`.
+ 
+ The restart sequence in ``scripts/mysql.server`` would fail to capture and return if the start call failed to start the server, so a restart could occur that failed upon start-up, and the script would still return ``0`` as if it worked without any issues. Bug fixed :bug:`1339894`.
+
+ Updating a unique key value could cause server hang if slave node has enabled parallel slaves. Bug fixed :bug:`1280896`.
+ 
+ |Percona XtraDB Cluster| has implemented threadpool scheduling fixes. Bug fixed :bug:`1333348`.
+
+ ``garbd`` was returning incorrect return code, ie. when ``garbd`` was already started, return code was ``0``. Bug fixed :bug:`1308103`.
+
+ :variable:`wsrep_sst_rsync` would silently fail on joiner when ``rsync`` server port was already taken. Bug fixed :bug:`1099783`.
+
+ Example ``wsrep_notify`` script failed on node shutdown. Bug fixed :bug:`1132955`.
+
+ When :variable:`gmcast.listen_addr` was configured to a certain address, local connection point for outgoing connections was not bound to listen address. This would happen if OS has multiple interfaces with IP addresses in the same subnet, it may happen that OS would pick wrong IP for local connection point and other nodes would see connections originating from IP address which was not listened to. Bug fixed :bug:`1240964`.
+
+ Issue with re-setting galera provider (in :variable:`wsrep_provider_options`) has been fixed. Bug fixed :bug:`1260283`.
+
+ Variable  :variable:`wsrep_provider_options` couldn't be set in runtime if no provider was loaded. Bug fixed :bug:`1260290`.
+
+ |Percona XtraDB Cluster| couldn't be built with *Bison* 3.0. Bug fixed :bug:`1262439`.
+
+ ``mysqld`` wasn't handling exceeding max writeset size wsrep error correctly. Bug fixed :bug:`1270920`.
+
+ When ``FLUSH TABLES WITH READ LOCK`` was used on a node with :variable:`wsrep_causal_reads` set to ``1`` while there was a ``DML`` on other nodes then, subsequent SELECTs/SHOW STATUS didn't hang earlier providing non-causal output, that has been fixed here. Bug fixed :bug:`1271177`.
+
+ Lowest group communication layer (evs) would fail to handle the situation properly when big number of nodes would suddenly start to see each other. Bugs fixed :bug:`1271918` and :bug:`1249805`.
+
+ |Percona XtraDB Cluster| server package no longer conflicts with ``mysql-libs`` package from *CentOS* repository. Bug fixed :bug:`1278516`.
+
+ The mysql-debug ``UNIV_DEBUG`` binary was missing from RPM/DEB server packages. Bug fixed :bug:`1290087`.
+ 
+ XtraBackup SST would fail if `progress <http://www.percona.com/doc/percona-xtradb-cluster/5.6/manual/xtrabackup_sst.html#progress>`_ option was used with large number of files. Bug fixed :bug:`1294431`.
+
+ When Query Cache was used and a node would go into non-PRIM state, queries which returned results earlier (and cached into query cache) would still return results whereas newer queries (or the ones not cached) would return ``unknown command``. Bug fixed :bug:`1296403`.
+
+ Brute Force abort did not work with INSERTs to table with single unique key. Bug fixed :bug:`1299116`.
+
+ |InnoDB| buffer pool dump and load was not working as expected due to :variable:`wsrep_recover` overwriting the buffer pool dump file. Bug fixed :bug:`1305955`.
+
+ Close referenced table opened in the same function when foreign constraints were checked, otherwise it could lead to server stall when running ``DROP TABLE``. Bug fixed :bug:`1309241`.
+
+ Compiling on *FreeBSD* 10.0 with ``CLANG`` would result in fatal error. Bug fixed :bug:`1309507`.
+
+ Truncating the sorted version of multi-byte character conversion could lead to wsrep certification failures. Bug fixed :bug:`1314854`.
+
+ Cluster node acting as async slave would stop with the wrong position after hitting :variable:`max_write_set_size`. Bug fixed :bug:`1309669`.
+
+ Fixed the events replication inconsistencies. Bug fixed :bug:`1312618`.
+
+ :variable:`wsrep_slave_threads` was counted towards :variable:`max_connections` which could cause ``ERROR 1040 (HY000): Too many connections`` error. Bug fixed :bug:`1315588`.
+
+ Leaving node was not set nonoperational if processed leave message originated from different view than the current one which could cause other nodes to crash. Bug fixed :bug:`1323412` (:githubbug:`41`).
+
+ ``garb`` couldn't be started with ``init`` script on *RHEL* 6.5. Bug fixed :bug:`1323652`.
+
+ SST would fail when binlogs were in dedicated directory that's located inside ``datadir``. This bug was a regression introduced by bug fix for :bug:`1273368`. Bug fixed :bug:`1326012`.
+
+ GTID of TOI operations is now also synced to |InnoDB| tablespace in order to get consistent backups. Bug fixed :bug:`1329055`.
+
+ ``mysql-debug`` is now distributed with binary ``tar.gz``  along with RPM and DEB packages. Bug fixed :bug:`1332073`.
+
+ Startup failure with ``Undetected state gap`` has been fixed. Bug fixed :bug:`1334606`.
+
+ Galera3 is now installed in ``/usr/lib/galera3/libgalera_smm.so`` with a  compatibility symlink to ``/usr/lib/libgalera_smm.so``. Bug fixed :bug:`1279328`.
+
+ Galera could not be compiled on PowerPC. Bug fixed :githubbug:`59`.
+
+ Cluster could stall if leaving node failed to acknowledge all messages it had received due to exception and remaining nodes failed to reach consensus because of that. Bug fixed :githubbug:`37`.  
+
+ When two node instances were set up on the same server with the two different IPs, they couldn't not work well because they were use wrong IP addresses. Bug fixed :githubbug:`31`.
+
+ Automated donor selection with segments gave inconsistent results. Bug fixed :githubbug:`29`.
+
+Other bug fixes: :bug:`1297822`, :bug:`1269811`, :bug:`1262887`, :bug:`1244835`, :bug:`1338995`, :githubbug:`11`, :githubbug:`40`, :githubbug:`38`, :githubbug:`33`, and :githubbug:`24`.
+
+Help us improve quality by reporting any bugs you encounter using our `bug tracking system <https://bugs.launchpad.net/percona-xtradb-cluster/+filebug>`_. As always, thanks for your continued support of Percona!
+
 
=== modified file 'doc-pxc/source/release-notes/release-notes_index.rst'
--- doc-pxc/source/release-notes/release-notes_index.rst	2014-03-20 09:43:39 +0000
+++ doc-pxc/source/release-notes/release-notes_index.rst	2014-07-18 11:34:40 +0000
@@ -6,6 +6,7 @@
    :maxdepth: 1
    :glob:
 
+   Percona-XtraDB-Cluster-5.6.19-25.6
    Percona-XtraDB-Cluster-5.6.15-25.5
    Percona-XtraDB-Cluster-5.6.15-25.4
    Percona-XtraDB-Cluster-5.6.15-25.3
 
=== modified file 'doc-pxc/source/wsrep-provider-index.rst'
--- doc-pxc/source/wsrep-provider-index.rst	2014-03-20 09:43:39 +0000
+++ doc-pxc/source/wsrep-provider-index.rst	2014-07-18 11:34:40 +0000
@@ -485,6 +485,16 @@
 
 When this variable is set to ``TRUE`` more recent primary component overrides older ones in case of conflicting prims.
 
+.. variable::  pc.recovery
+
+   :cli: Yes
+   :conf: Yes
+   :scope: Global
+   :dyn: No
+   :default: true
+
+When this variable is set to ``true`` the node stores the Primary Component state to disk. The Primary Component can then recover automatically when all nodes that were part of the last saved state re-establish communications with each other. This feature allows automatic recovery from full cluster crashes, such as in the case of a data center power outage and graceful full cluster restarts without the need for explicitly bootstrapping a new Primary Component.
+
 .. variable::  pc.version
 
    :cli: Yes
 
=== modified file 'doc-pxc/source/wsrep-status-index.rst'
--- doc-pxc/source/wsrep-status-index.rst	2014-01-29 15:10:12 +0000
+++ doc-pxc/source/wsrep-status-index.rst	2014-07-18 11:34:40 +0000
@@ -135,6 +135,10 @@
 .. variable:: wsrep_incoming_addresses
 
 Shows the comma-separated list of incoming node addresses in the cluster.
+
+.. variable:: wsrep_evs_repl_latency
+
+This status variable provides the information regarding the group communication replication latency. This latency is measured from the time point when a message is sent out to the time point when a message is received.
   
 .. variable:: wsrep_cluster_conf_id
 
 
=== modified file 'doc-pxc/source/wsrep-system-index.rst'
--- doc-pxc/source/wsrep-system-index.rst	2014-03-20 12:59:52 +0000
+++ doc-pxc/source/wsrep-system-index.rst	2014-07-18 11:34:40 +0000
@@ -231,7 +231,7 @@
    :scope: Global
    :dyn: Yes
 
-This variable is used to set the notification `command <http://www.codership.com/wiki/doku.php?id=notification_command>`_ that server will execute every time cluster membership or local node status changes.
+This variable is used to set the notification `command <http://galeracluster.com/documentation-webpages/notification-cmd.html>`_ that server will execute every time cluster membership or local node status changes.
 
 .. variable:: wsrep_on
 
@@ -309,6 +309,16 @@
 
 This variable controls if *MyISAM* will be replicated or not. *MyISAM* replication is still experimental and that is one of the reasons why this variable is set to ``OFF`` by default. 
 
+.. variable:: wsrep_restart_slave
+
+   :cli: Yes
+   :conf: Yes
+   :scope: Global
+   :dyn: Yes
+   :default: OFF
+
+This variable controls if |MySQL| slave should be restarted automatically, when node joins back to cluster, because asynchronous replication slave thread is stopped when the node tries to apply next replication event while the node is in non-primary state.
+
 .. variable:: wsrep_retry_autocommit
 
    :cli: Yes
@@ -319,6 +329,26 @@
 
 This variable sets the number of times autocommitted transactions will be tried in the cluster if it encounters certification errors. In case there is a conflict, it should be safe for the cluster node to simply retry the statement without the client's knowledge with the hopes that it will pass the next time. This can be useful to help an application using autocommit to avoid the deadlock errors that can be triggered by replication conflicts. If this variable is set to ``0`` transaction won't be retried and if it is set to ``1`` it will be retried once.
 
+.. variable:: wsrep_slave_FK_checks
+
+   :cli: Yes
+   :conf: Yes
+   :scope: Global
+   :dyn: Yes
+   :default: ON
+
+This variable is used to control if Foreign Key checking is done for applier threads.
+
+.. variable:: wsrep_slave_UK_checks
+
+   :cli: Yes
+   :conf: Yes
+   :scope: Global
+   :dyn: Yes
+   :default: OFF
+
+This variable is used to control if Unique Key checking is done for applier threads.
+
 .. variable:: wsrep_slave_threads
 
    :cli: Yes
@@ -327,7 +357,7 @@
    :dyn: Yes
    :default: 1
 
-This variable controls the number of threads that can apply replication transactions in parallel. Galera supports true parallel replication, replication that applies transactions in parallel only when it is safe to do so. The variable is dynamic, you can increase/decrease it anytime, note that, when you decrease it, it won't kill the threads immediately but stop them after they are done applying current transaction (the effect with increase is immediate though).  If any replication consistency problems are encountered, it's recommended to set this back to ``1`` to see if that resolves the issue. The default value can be increased for better throughput. You may want to increase it many a time as suggested `in Codership documentation <http://www.codership.com/wiki/doku.php?id=flow_control>`_, in JOINED state for instance to speed up the catchup process to SYNCED. You can also estimate the optimal value for this from :variable:`wsrep_cert_deps_distance` as suggested `on this page <http://www.codership.com/wiki/doku.php?id=monitoring#checking_replication_health>`_. You can also refer to `this <http://www.codership.com/wiki/doku.php?id=configuration_tips#parallel_applying_wsrep_slave_threads>`_ for more configuration tips.
+This variable controls the number of threads that can apply replication transactions in parallel. Galera supports true parallel replication, replication that applies transactions in parallel only when it is safe to do so. The variable is dynamic, you can increase/decrease it anytime, note that, when you decrease it, it won't kill the threads immediately but stop them after they are done applying current transaction (the effect with increase is immediate though).  If any replication consistency problems are encountered, it's recommended to set this back to ``1`` to see if that resolves the issue. The default value can be increased for better throughput. You may want to increase it many a time as suggested `in Codership documentation <http://galeracluster.com/documentation-webpages/nodestates.html#flow-control>`_, in ``JOINED`` state for instance to speed up the catchup process to ``SYNCED``. You can also estimate the optimal value for this from :variable:`wsrep_cert_deps_distance` as suggested `on this page <http://galeracluster.com/documentation-webpages/monitoringthecluster.html#checking-the-replication-health>`_. You can also refer to `this <http://galeracluster.com/documentation-webpages/configurationtips.html#setting-parallel-slave-threads>`_ for more configuration tips.
 
 .. variable:: wsrep_sst_auth
 
@@ -372,7 +402,7 @@
  * xtrabackup-v2 - This is same as xtrabackup SST except that it uses newer protocol, hence is not compatible. This is the **recommended** option for PXC 5.5.34 and above. For more details, please check :ref:`xtrabackup_sst` and :ref:`errata`. This is also the default SST method. For SST with older nodes (< 5.5.34), use xtrabackup as the SST method.
  * rsync - uses ``rsync`` to perform the SST, this method doesn't use the :variable:`wsrep_sst_auth`
  * mysqldump - uses ``mysqldump`` to perform the SST, this method requires :variable:`wsrep_sst_auth` to be set up with <user>:<password>, where user has root privileges on the server.
- * custom_script_name - Galera supports `Scriptable State Snapshot Transfer <http://www.codership.com/wiki/doku.php?id=scriptable_state_snapshot_transfer>`_. This enables users to create their own custom script for performing an SST.
+ * custom_script_name - Galera supports `Scriptable State Snapshot Transfer <http://galeracluster.com/documentation-webpages/statetransfer.html#scriptable-state-snapshot-transfer>`_. This enables users to create their own custom script for performing an SST.
  * skip - this option can be used to skip the SST, it can be used when initially starting the cluster and manually restore the same data to all nodes. It shouldn't be used as permanent setting because it could lead to data inconsistency across the nodes.
 
 .. note::