with <option>-b</option>
   and user-provided scripts specified with <option>-f</option>.
   Each script may be given a relative weight specified after an
   <literal>@</literal> so as to change its selection probability.
   The default weight is <literal>1</literal>.
   Scripts with a weight of <literal>0</literal> are ignored.
 </para>

  <para>
   The default built-in transaction script (also invoked with <option>-b tpcb-like</option>)
   issues seven commands per transaction over randomly chosen <literal>aid</literal>,
   <literal>tid</literal>, <literal>bid</literal> and <literal>delta</literal>.
   The scenario is inspired by the TPC-B benchmark, but is not actually TPC-B,
   hence the name.
  </para>

  <orderedlist>
   <listitem><para><literal>BEGIN;</literal></para></listitem>
   <listitem><para><literal>UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;</literal></para></listitem>
   <listitem><para><literal>SELECT abalance FROM pgbench_accounts WHERE aid = :aid;</literal></para></listitem>
   <listitem><para><literal>UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;</literal></para></listitem>
   <listitem><para><literal>UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;</literal></para></listitem>
   <listitem><para><literal>INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);</literal></para></listitem>
   <listitem><para><literal>END;</literal></para></listitem>
  </orderedlist>

  <para>
   If you select the <literal>simple-update</literal> built-in (also <option>-N</option>),
   steps 4 and 5 aren't included in the transaction.
   This will avoid update contention on these tables, but
   it makes the test case even less like TPC-B.
  </para>

  <para>
   If you select the <literal>select-only</literal> built-in (also <option>-S</option>),
   only the <command>SELECT</command> is issued.
  </para>
 </refsect2>

 <refsect2>
  <title>Custom Scripts</title>

  <para>
   <application>pgbench</application> has support for running custom
   benchmark scenarios by replacing the default transaction script
   (described above) with a transaction script read from a file
   (<option>-f</option> option).  In this case a <quote>transaction</quote>
   counts as one execution of a script file.
  </para>

  <para>
   A script file contains one or more SQL commands terminated by
   semicolons.  Empty lines and lines beginning with
   <literal>--</literal> are ignored.  Script files can also contain
   <quote>meta commands</quote>, which are interpreted by <application>pgbench</application>
   itself, as described below.
  </para>

  <note>
   <para>
    Before <productname>PostgreSQL</productname> 9.6, SQL commands in script files
    were terminated by newlines, and so they could not be continued across
    lines.  Now a semicolon is <emphasis>required</emphasis> to separate consecutive
    SQL commands (though an SQL command does not need one if it is followed
    by a meta command).  If you need to create a script file that works with
    both old and new versions of <application>pgbench</application>, be sure to write
    each SQL command on a single line ending with a semicolon.
   </para>
   <para>
    It is assumed that <application>pgbench</application> scripts do not contain
    incomplete blocks of SQL
    transactions. If at runtime the client reaches the end of the script without
    completing the last transaction block, it will be aborted.
   </para>
  </note>

  <para>
   There is a simple variable-substitution facility for script files.
   Variable names must consist of letters (including non-Latin letters),
   digits, and underscores, with the first character not being a digit.
   Variables can be set by the command-line <option>-D</option> option,
   explained above, or by the meta commands explained below.
   In addition to any variables preset by <option>-D</option> command-line options,