php-doc-en/reference/mongo/mongocursor/batchsize.xml

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<refentry xml:id="mongocursor.batchsize" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>MongoCursor::batchSize</refname>
  <refpurpose>Limits the number of elements returned in one batch.</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <modifier>public</modifier> <type>MongoCursor</type><methodname>MongoCursor::batchSize</methodname>
   <methodparam><type>int</type><parameter>batchSize</parameter></methodparam>
  </methodsynopsis>
  <para>
   A cursor typically fetches a batch of result objects and store them
   locally. This method sets the batchSize value to configure the amount of
   documents retrieved from the server in one data packet. However, it will
   never return more documents than fit in the max batch size limit (usually
   4MB).  
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;  
  <para>
   <variablelist>
    <varlistentry>
     <term>
      <parameter>batchSize</parameter>
     </term>
     <listitem>
      <para>
       The number of results to return per batch. Each batch requires a
       round-trip to the server. 
      </para>
      <para>
       If <parameter>batchSize</parameter> is <emphasis>2 or
       more</emphasis>, it represents the size of each batch of objects retrieved.
       It can be adjusted to optimize performance and limit data transfer.
      </para>
      <para>
       If <parameter>batchSize</parameter> is <literal>1</literal> or negative, it
       will limit of number returned documents to the absolute value of batchSize,
       and the cursor will be closed. For example if
       batchSize is <literal>-10</literal>, then the server will return a maximum
       of 10 documents and as many as can fit in 4MB, then close the cursor.
      </para>
      <warning>
       <para>
        A <parameter>batchSize</parameter> of <literal>1</literal> is special, and
        means the same as <literal>-1</literal>, i.e. a value of
        <literal>1</literal> makes the cursor only capable of returning
        <emphasis>one</emphasis> document.
       </para>
      </warning>
      <para>
       Note that this feature is different from
       <function>MongoCursor::limit</function> in that documents must fit within a
       maximum size, and it removes the need to send a request to close the cursor
       server-side. The batch size can be changed even after a cursor is iterated,
       in which case the setting will apply on the next batch retrieval. 
      </para>
      <para>
       This cannot override MongoDB's limit on the amount of data it will return to 
       the client (i.e., if you set batch size to 1,000,000,000, MongoDB will still 
       only return 4-16MB of results per batch). 
      </para>
      <para>
       To ensure consistent behavior, the rules of
       <function>MongoCursor::batchSize</function> and
       <function>MongoCursor::limit</function> behave a 
       little complex but work "as expected".  The rules are: hard limits override 
       soft limits with preference given to <function>MongoCursor::limit</function>
       over <function>MongoCursor::batchSize</function>.  After that, whichever is 
       set and lower than the other will take precedence. See below.
       section for some examples.
      </para>
     </listitem>
    </varlistentry>   
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;  
  <para>
   Returns this cursor.
  </para>
 </refsect1>

 <refsect1 role="errors">
  &reftitle.errors;
  <para>
   Throws <classname>MongoCursorException</classname> if this cursor has 
   started iterating.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <example>
   <title><function>MongoCursor::batchSize</function> and combinations with
   <function>MongoCursor::limit</function></title>
   <programlisting role="php">
<![CDATA[
<?php

// one batch, at most 10 items. The -10 makes the server to return 10 items,
// and then remove the cursor.
$cursor->limit(20)->batchSize(-10);

// first batch: at most 10 items
$cursor->limit(10);

// first batch: at most 10 items
$cursor->limit(10)->batchSize(20);

// results are fetched in batches of 10 each, with a maximum of 20 items
// returned (that means two batches of 10).
$cursor->limit(20)->batchSize(10);

// results are fetched in batches of 7 each, with a maximum of 30 items
// returned (that means that the driver requests 4 batches of 7, and one batch
// of 2).
$cursor->limit(30)->batchSize(7)
?>
]]>
   </programlisting>
  </example>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   MongoDB core docs on <link xlink:href="&url.mongodb.dochub.limit;">limit</link>.
  </para>
  <para>
   <simplelist>
    <member><function>MongoCursor::limit</function></member>
   </simplelist>
  </para>
 </refsect1>
</refentry>
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