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Assorted updates and some more additional notes in the service level concepts section. Service level concepts should get more hints on SHOW SLAVE STATUS, maybe. We have them elsewhere already.

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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@321019 c90b9560-bf6c-de11-be94-00142212c4b1
This commit is contained in:
Ulf Wendel 2011-12-14 17:11:20 +00:00
parent 3bb8c62d1a
commit 4511dd704d
2 changed files with 76 additions and 12 deletions
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60
reference/mysqlnd_ms/concepts.xml
View file

@ -987,6 +987,16 @@ version = 5.6.2-m5-log
</listitem>
</itemizedlist>
</para>
<para>
Depending how a cluster is used it may be possible to achieve higher service
levels than the default one. For example, a read from an asynchronous
MySQL replication slave is eventual consistent. Thus, one may say the default
consistency level of a MySQL replication cluster is eventual consistency.
However, if the master only is used by a client for reading and writing during a
session, session consistency (read your writes) is given. PECL mysqlnd 1.2.0
abstracts the details of choosing an appropriate node for any of the above
service levels from the user.
</para>
<para>
Service levels can be set through the qualify-of-service filter in the
<link linkend="mysqlnd-ms.plugin-ini-json">plugins configuration file</link>
@ -1039,6 +1049,56 @@ version = 5.6.2-m5-log
The latter requires the use of
<link linkend="mysqlnd-ms.gtid">client-side global transaction id injection</link>.
</para>
<para>
<emphasis role="bold">Advantages of the new approach</emphasis>
</para>
<para>
The new approach supersedes the use of SQL hints and the configuration option
<literal>master_on_write</literal> in some respects. If an application
running on top of an asynchonous MySQL replication cluster cannot accept stale
data for certain reads, it is easier to tell the plugin to choose appropriate
nodes than prefixing all read statements in question with the SQL hint
to enforce the use of the master. Furthermore, the plugin may be able to
use selected slaves for reading.
</para>
<para>
The <literal>master_on_write</literal> configuration option makes the plugin
use the master after the first write (session consistency, read your writes).
In some cases, session consistency may not be needed for the rest of the session
but only for some, few read operations. Thus, <literal>master_on_write</literal>
may result in more read load on the master than necessary. In those cases it
is better to request a higher than default service level only for those reads
that actually need it. Once the reads are done, the application can return to
default service level. Switching between service levels is only possible
using <link linkend="function.mysqlnd-ms-set-qos"><function>mysqlnd_ms_set_qos</function></link>.
</para>
<para>
<emphasis role="bold">Performance considerations</emphasis>
</para>
<para>
A MySQL replication cluster cannot tell clients which slaves are capable
of delivering which level of service. Thus, in some cases,
clients need to query the slaves to check their status.
PECL mysqlnd_ms transparently runs the necessary SQL in the
background. However, this is an expensive and slow operation. SQL statements
are run if eventual consistency is combined with an age (slave lag) limit and
if session consistency is combined with a global transaction ID.
</para>
<para>
If no parameters and options are set, no SQL is needed. In that case,
the plugin consider all nodes of the type shown below.
<itemizedlist>
<listitem>
<simpara>eventual consistency, no further options set: all masters, all slaves</simpara>
</listitem>
<listitem>
<simpara>session consistency, no further options set: all masters</simpara>
</listitem>
<listitem>
<simpara>strong consistency (no options allowed): all masters</simpara>
</listitem>
</itemizedlist>
</para>
</section>
<section xml:id="mysqlnd-ms.gtid">

28
reference/mysqlnd_ms/quickstart.xml
View file

@ -740,7 +740,7 @@ $mysqli->close();
</para>
<para>
<example>
<title>Outlook: transaction aware</title>
<title>Transaction aware</title>
<programlisting role="php">
<![CDATA[
<?php
@ -1120,7 +1120,7 @@ PHP Warning: mysqli::query(): (mysqlnd_ms) No connection selected by the last f
<para>
First, create a counter table on your master server and insert a record into it.
The plugin does not assist creating the table.
Database administrators must make sure it exists. Depending on the error
Database administrators must make sure it exists. Depending on the error
reporting mode, the plugin will silently ignore the lack of the table or bail out.
</para>
<para>
@ -1144,7 +1144,7 @@ INSERT INTO `trx`(`trx_id`) VALUES (1);
section. Make sure the table name used for the <literal>UPDATE</literal>
statement is fully qualified. In the example,
<literal>test.trx</literal> is used to refer to table <literal>trx</literal>
in the schema <literal>test</literal>. Use the table that was created in
in the schema (database) <literal>test</literal>. Use the table that was created in
the previous step. It is important to set the fully qualified table name
because the connection on which the injection is done may use a different
default database. Make sure the user that opens the connection
@ -1229,8 +1229,8 @@ array(1) {
The example runs three statements in auto commit mode on the master, causing
three transactions on the master. For every such statement, the plugin will
inject the configured <literal>UPDATE</literal> transparently before executing
the users SQL statement. After the example script has finished the global
transaciton ID counter on the master has been incremented by three.
the users SQL statement. When the script ends the global
transaction ID counter on the master has been incremented by three.
</para>
<para>
The fourth SQL statement executed in the example, a <literal>SELECT</literal>,
@ -1311,13 +1311,17 @@ GTID after transaction 8
</example>
</para>
<para>
Applications can ask mysqlnd_ms for a global transaction ID which
belongs to the last write transactions. The function <literal>mysqlnd_ms_get_last_gtid()</literal>
may be called after the GTID has been incremented. The
function returns the GTID obtained when executing the SQL statement from
Applications can ask PECL mysqlnd_ms for a global transaction ID which
belongs to the last write operation performed by the application.
The function <function>mysqlnd_ms_get_last_gtid</function> returns the
GTID obtained when executing the SQL statement from
the <literal>fetch_last_gtid</literal> entry of the
<literal>global_transaction_id_injection</literal> section from
the plugins configuration file. Applications are advices not to run the SQL
the plugins configuration file. The function may be called
after the GTID has been incremented.
</para>
<para>
Applications are adviced not to run the SQL
statement themselves as this bares the risk of accidently causing an implicit
GTID increment. Also, if the function is used, it is easy to migrate
an application from one SQL statement for fetching a transaction ID to another,
@ -1398,7 +1402,7 @@ var_dump($res->fetch_assoc());
</example>
</para>
<para>
A GTID returned from <literal>mysqlnd_ms_get_last_gtid()</literal>
A GTID returned from <function>mysqlnd_ms_get_last_gtid</function>
can be used as an option for the session consistency service level.
Session consistency delivers read your writes. Session consistency can
be requested by calling
@ -1408,7 +1412,7 @@ var_dump($res->fetch_assoc());
the previous <literal>INSERT</literal> already.
</para>
<para>
PECL/mysqlnd_ms will transparently check every configured slave if
PECL mysqlnd_ms will transparently check every configured slave if
it has replicated the <literal>INSERT</literal> by checking the slaves
GTID table. The check is done running the SQL set with the
<literal>check_for_gtid</literal> option from the