75 lines
2.9 KiB
XML
75 lines
2.9 KiB
XML
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<chapter id="ljp.prog-guide.database">
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<title>Database</title>
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<itemizedlist>
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<title>Database</title>
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<listitem><simpara>
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Check your db index usage... mysql's <function>EXPLAIN</function> is your friend.
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</simpara></listitem>
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<listitem><simpara>
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Between <function>LOCK TABLES</function> & <function>UNLOCK TABLES</function>,
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never call a subroutine.
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</simpara></listitem>
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<listitem><simpara>
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Check the DB error code after an SQL statement. Just because it worked once and the SQL is correct,
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that doesn't mean the table might not go corrupt, a disk might fill up, or index space within the
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file might not fill up. Errors happen. Deal with them.
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</simpara></listitem>
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<listitem><simpara>
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Preferred way to break up a long SQL query:
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<programlisting>
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$sth = $dbh->prepare("SELECT cola, colb, colc, cold FROM foo ".
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"WHERE colb<>cola AND colc=22");
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</programlisting>
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</simpara></listitem>
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<listitem><para>
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Note on variable naming:
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<informaltable>
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<tgroup cols="2">
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<tbody>
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<row>
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<entry><varname>$sth</varname></entry>
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<entry>statement handle</entry>
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</row>
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<row>
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<entry><varname>$dbh</varname></entry>
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<entry>one database handle (usually the master)</entry>
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</row>
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<row>
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<entry><varname>$dbs</varname></entry>
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<entry>set of database handles [master(, slave)]</entry>
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</row>
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<row>
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<entry><varname>$dbr</varname></entry>
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<entry>read-only slave db handle (used for selects)</entry>
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</row>
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<row>
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<entry><varname>$dbarg</varname></entry>
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<entry>argument that can take a <varname>$dbh/r</varname> or <varname>$dbs</varname></entry>
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</row>
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<row>
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<entry><varname>$remote</varname></entry>
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<entry>hashref of remote user, based on cookies. will contain 'userid' and 'user' params,
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unless faster get_remote_noauth was used, in which case only 'user' will be present.</entry>
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</row>
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<row>
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<entry><varname>$u</varname></entry>
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<entry>a user 'object' (a hashref)</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</para></listitem>
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<listitem><simpara>
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Call for database handles as you need them, instead of predeclaring <varname>$db<replaceable>x</replaceable></varname> variables.
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Use <function>LJ::get_db_writer</function> to get a writable handle to the database, and
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<function>LJ::get_db_reader</function> to get a read-only handle.
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</simpara></listitem>
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</itemizedlist>
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</chapter>
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<!--
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Local Variables:
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mode:sgml
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sgml-parent-document: ("index.xml" "part" "chapter")
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End:
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-->
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