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193 <div class=
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"working-with-data-on-the-server-in-an-atomic-fashion">
194 <h1>Working with data on the server in an atomic fashion
<a class=
"headerlink" href=
"#working-with-data-on-the-server-in-an-atomic-fashion" title=
"Permalink to this headline">¶
</a></h1>
195 <div class=
"section" id=
"synopsis">
196 <span id=
"index-0"></span><h2>SYNOPSIS
<a class=
"headerlink" href=
"#synopsis" title=
"Permalink to this headline">¶
</a></h2>
197 <p>#include
<libmemcached/memcached.h
></p>
198 <dl class=
"function">
199 <dt id=
"_CPPv413memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t">
200 <span id=
"_CPPv313memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t"></span><span id=
"_CPPv213memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t"></span><span id=
"memcached_cas__memcached_stP.cCP.s.cCP.s.time_t.uint32_t.uint64_t"></span><a class=
"reference internal" href=
"memcached_return_t.html#_CPPv418memcached_return_t" title=
"memcached_return_t">memcached_return_t
</a> <code class=
"sig-name descname">memcached_cas
</code><span class=
"sig-paren">(
</span><a class=
"reference internal" href=
"memcached_create.html#_CPPv412memcached_st" title=
"memcached_st">memcached_st
</a> *
<em>ptr
</em>,
<em class=
"property">const
</em> char *
<em>key
</em>, size_t
<em>key_length
</em>,
<em class=
"property">const
</em> char *
<em>value
</em>, size_t
<em>value_length
</em>, time_t
<em>expiration
</em>, uint32_t
<em>flags
</em>, uint64_t
<em>cas
</em><span class=
"sig-paren">)
</span><a class=
"headerlink" href=
"#_CPPv413memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title=
"Permalink to this definition">¶
</a><br /></dt>
203 <dl class=
"function">
204 <dt id=
"_CPPv420memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t">
205 <span id=
"_CPPv320memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t"></span><span id=
"_CPPv220memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t"></span><span id=
"memcached_cas_by_key__memcached_stP.cCP.s.cCP.s.cCP.s.time_t.uint32_t.uint64_t"></span><a class=
"reference internal" href=
"memcached_return_t.html#_CPPv418memcached_return_t" title=
"memcached_return_t">memcached_return_t
</a> <code class=
"sig-name descname">memcached_cas_by_key
</code><span class=
"sig-paren">(
</span><a class=
"reference internal" href=
"memcached_create.html#_CPPv412memcached_st" title=
"memcached_st">memcached_st
</a> *
<em>ptr
</em>,
<em class=
"property">const
</em> char *
<em>group_key
</em>, size_t
<em>group_key_length
</em>,
<em class=
"property">const
</em> char *
<em>key
</em>, size_t
<em>key_length
</em>,
<em class=
"property">const
</em> char *
<em>value
</em>, size_t
<em>value_length
</em>, time_t
<em>expiration
</em>, uint32_t
<em>flags
</em>, uint64_t
<em>cas
</em><span class=
"sig-paren">)
</span><a class=
"headerlink" href=
"#_CPPv420memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title=
"Permalink to this definition">¶
</a><br /></dt>
208 <p>Compile and link with -lmemcached
</p>
210 <div class=
"section" id=
"description">
211 <h2>DESCRIPTION
<a class=
"headerlink" href=
"#description" title=
"Permalink to this headline">¶
</a></h2>
212 <p><a class=
"reference internal" href=
"#_CPPv413memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title=
"memcached_cas"><code class=
"xref cpp cpp-func docutils literal notranslate"><span class=
"pre">memcached_cas()
</span></code></a> overwrites data in the server as long as the “cas”
213 value is still the same in the server. You can get the cas value of a result
214 by calling
<a class=
"reference internal" href=
"memcached_result_st.html#_CPPv420memcached_result_casPK19memcached_result_st" title=
"memcached_result_cas"><code class=
"xref cpp cpp-func docutils literal notranslate"><span class=
"pre">memcached_result_cas()
</span></code></a> on a memcached_result_st(
3)
215 structure. At the point that this note was written cas is still buggy in memcached.
216 Turning on tests for it in libmemcached(
3) is optional. Please see
217 <a class=
"reference internal" href=
"memcached_set.html#_CPPv413memcached_setP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t" title=
"memcached_set"><code class=
"xref cpp cpp-func docutils literal notranslate"><span class=
"pre">memcached_set()
</span></code></a> for information on how to do this.
</p>
218 <p><a class=
"reference internal" href=
"#_CPPv420memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title=
"memcached_cas_by_key"><code class=
"xref cpp cpp-func docutils literal notranslate"><span class=
"pre">memcached_cas_by_key()
</span></code></a> method behaves in a similar method as the non
219 key methods. The difference is that it uses the group_key parameter
220 to map objects to particular servers.
</p>
221 <p><a class=
"reference internal" href=
"#_CPPv413memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title=
"memcached_cas"><code class=
"xref cpp cpp-func docutils literal notranslate"><span class=
"pre">memcached_cas()
</span></code></a> is tested with the
<a class=
"reference internal" href=
"memcached_behavior.html#_CPPv4N20memcached_behavior_t26MEMCACHED_BEHAVIOR_USE_UDPE" title=
"MEMCACHED_BEHAVIOR_USE_UDP"><code class=
"xref cpp cpp-any docutils literal notranslate"><span class=
"pre">MEMCACHED_BEHAVIOR_USE_UDP
</span></code></a> behavior enabled. However, when using these operations with this behavior
222 on, there are limits to the size of the payload being sent to the server. The
223 reason for these limits is that the Memcached Server does not allow
224 multi-datagram requests and the current server implementation sets a datagram
225 size to
1400 bytes. Due to protocol overhead, the actual limit of the user
226 supplied data is less than
1400 bytes and depends on the protocol in use as,
227 well as the operation being executed. When running with the binary protocol,
228 <a class=
"reference internal" href=
"memcached_behavior.html#_CPPv4N20memcached_behavior_t34MEMCACHED_BEHAVIOR_BINARY_PROTOCOLE" title=
"MEMCACHED_BEHAVIOR_BINARY_PROTOCOL"><code class=
"xref cpp cpp-any docutils literal notranslate"><span class=
"pre">MEMCACHED_BEHAVIOR_BINARY_PROTOCOL
</span></code></a>, the size of the key,value,
229 flags and expiry combined may not exceed
1368 bytes. When running with the
230 ASCII protocol, the exact limit fluctuates depending on which function is
231 being executed and whether the function is a cas operation or not. For
232 non-cas ASCII set operations, there are at least
1335 bytes available to
233 split among the key, key_prefix, and value; for cas ASCII operations there
234 are at least
1318 bytes available to split among the key, key_prefix and value. If the total size of the command, including overhead, exceeds
1400 bytes, a
<a class=
"reference internal" href=
"memcached_return_t.html#_CPPv4N18memcached_return_t23MEMCACHED_WRITE_FAILUREE" title=
"MEMCACHED_WRITE_FAILURE"><code class=
"xref cpp cpp-any docutils literal notranslate"><span class=
"pre">MEMCACHED_WRITE_FAILURE
</span></code></a> will be returned.
</p>
236 <div class=
"section" id=
"return">
237 <h2>RETURN
<a class=
"headerlink" href=
"#return" title=
"Permalink to this headline">¶
</a></h2>
238 <p>All methods return a value of type
<a class=
"reference internal" href=
"memcached_return_t.html#_CPPv418memcached_return_t" title=
"memcached_return_t"><code class=
"xref cpp cpp-type docutils literal notranslate"><span class=
"pre">memcached_return_t
</span></code></a>.
239 On success the value will be
<a class=
"reference internal" href=
"memcached_return_t.html#_CPPv4N18memcached_return_t17MEMCACHED_SUCCESSE" title=
"MEMCACHED_SUCCESS"><code class=
"xref cpp cpp-any docutils literal notranslate"><span class=
"pre">MEMCACHED_SUCCESS
</span></code></a>.
240 Use
<a class=
"reference internal" href=
"memcached_strerror.html#_CPPv418memcached_strerrorP12memcached_st18memcached_return_t" title=
"memcached_strerror"><code class=
"xref cpp cpp-func docutils literal notranslate"><span class=
"pre">memcached_strerror()
</span></code></a> to translate this value to a printable
243 <div class=
"section" id=
"see-also">
244 <h2>SEE ALSO
<a class=
"headerlink" href=
"#see-also" title=
"Permalink to this headline">¶
</a></h2>
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