cassandra-commits mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From tylerho...@apache.org
Subject svn commit: r1663774 - in /cassandra/site/publish/doc/cql3: CQL-2.0.html CQL-2.1.html
Date Tue, 03 Mar 2015 20:05:46 GMT
Author: tylerhobbs
Date: Tue Mar  3 20:05:46 2015
New Revision: 1663774

URL: http://svn.apache.org/r1663774
Log:
Update CQL3 docs for CASSANDRA-8889

Modified:
    cassandra/site/publish/doc/cql3/CQL-2.0.html
    cassandra/site/publish/doc/cql3/CQL-2.1.html

Modified: cassandra/site/publish/doc/cql3/CQL-2.0.html
URL: http://svn.apache.org/viewvc/cassandra/site/publish/doc/cql3/CQL-2.0.html?rev=1663774&r1=1663773&r2=1663774&view=diff
==============================================================================
--- cassandra/site/publish/doc/cql3/CQL-2.0.html (original)
+++ cassandra/site/publish/doc/cql3/CQL-2.0.html Tue Mar  3 20:05:46 2015
@@ -38,7 +38,7 @@
 
   <properties> ::= <property> (AND <property>)*
     <property> ::= <identifier> '=' ( <identifier> | <constant> | <map-literal> )
-</pre></pre><p><br/>Please note that not every possible productions of the grammar above will be valid in practice. Most notably, <code>&lt;variable></code> and nested <code>&lt;collection-literal></code> are currently not allowed inside <code>&lt;collection-literal></code>.</p><p>A <code>&lt;variable></code> can be either anonymous (a question mark (<code>?</code>)) or named (an identifier preceded by <code>:</code>). Both declare a bind variables for <a href="#preparedStatement">prepared statements</a>. The only difference between an anymous and a named variable is that a named one will be easier to refer to (how exactly depends on the client driver used).</p><p>The <code>&lt;properties></code> production is use by statement that create and alter keyspaces and tables. Each <code>&lt;property></code> is either a <em>simple</em> one, in which case it just has a value, or a <em>map</em> one, in which case it&#8217;s value is a map grouping sub-options. The following will refer to one
  or the other as the <em>kind</em> (<em>simple</em> or <em>map</em>) of the property.</p><p>A <code>&lt;tablename></code> will be used to identify a table. This is an identifier representing the table name that can be preceded by a keyspace name. The keyspace name, if provided, allow to identify a table in another keyspace than the currently active one (the currently active keyspace is set through the <a href="#useStmt"><tt>USE</tt></a> statement).</p><p>For supported <code>&lt;function></code>, see the section on <a href="#functions">functions</a>.</p><h3 id="preparedStatement">Prepared Statement</h3><p>CQL supports <em>prepared statements</em>. Prepared statement is an optimization that allows to parse a query only once but execute it multiple times with different concrete values.</p><p>In a statement, each time a column value is expected (in the data manipulation and query statements), a <code>&lt;variable></code> (see above) can be used instead. A statement with bind variables m
 ust then be <em>prepared</em>. Once it has been prepared, it can executed by providing concrete values for the bind variables. The exact procedure to prepare a statement and execute a prepared statement depends on the CQL driver used and is beyond the scope of this document.</p><h2 id="dataDefinition">Data Definition</h2><h3 id="createKeyspaceStmt">CREATE KEYSPACE</h3><p><i>Syntax:</i></p><pre class="syntax"><pre>&lt;create-keyspace-stmt> ::= CREATE KEYSPACE (IF NOT EXISTS)? &lt;identifier> WITH &lt;properties>
+</pre></pre><p><br/>Please note that not every possible productions of the grammar above will be valid in practice. Most notably, <code>&lt;variable></code> and nested <code>&lt;collection-literal></code> are currently not allowed inside <code>&lt;collection-literal></code>.</p><p>A <code>&lt;variable></code> can be either anonymous (a question mark (<code>?</code>)) or named (an identifier preceded by <code>:</code>). Both declare a bind variables for <a href="#preparedStatement">prepared statements</a>. The only difference between an anymous and a named variable is that a named one will be easier to refer to (how exactly depends on the client driver used).</p><p>The <code>&lt;properties></code> production is use by statement that create and alter keyspaces and tables. Each <code>&lt;property></code> is either a <em>simple</em> one, in which case it just has a value, or a <em>map</em> one, in which case it&#8217;s value is a map grouping sub-options. The following will refer to one
  or the other as the <em>kind</em> (<em>simple</em> or <em>map</em>) of the property.</p><p>A <code>&lt;tablename></code> will be used to identify a table. This is an identifier representing the table name that can be preceded by a keyspace name. The keyspace name, if provided, allow to identify a table in another keyspace than the currently active one (the currently active keyspace is set through the <a href="#useStmt"><tt>USE</tt></a> statement).</p><p>For supported <code>&lt;function></code>, see the section on <a href="#functions">functions</a>.</p><h3 id="preparedStatement">Prepared Statement</h3><p>CQL supports <em>prepared statements</em>. Prepared statement is an optimization that allows to parse a query only once but execute it multiple times with different concrete values.</p><p>In a statement, each time a column value is expected (in the data manipulation and query statements), a <code>&lt;variable></code> (see above) can be used instead. A statement with bind variables m
 ust then be <em>prepared</em>. Once it has been prepared, it can executed by providing concrete values for the bind variables. The exact procedure to prepare a statement and execute a prepared statement depends on the CQL driver used and is beyond the scope of this document.</p><p>In addition to providing column values, bind markers may be used to provide values for <code>LIMIT</code>, <code>TIMESTAMP</code>, and <code>TTL</code> clauses.  If anonymous bind markers are used, the names for the query parameters will be <code>[limit]</code>, <code>[timestamp]</code>, and <code>[ttl]</code>, respectively.</p><h2 id="dataDefinition">Data Definition</h2><h3 id="createKeyspaceStmt">CREATE KEYSPACE</h3><p><i>Syntax:</i></p><pre class="syntax"><pre>&lt;create-keyspace-stmt> ::= CREATE KEYSPACE (IF NOT EXISTS)? &lt;identifier> WITH &lt;properties>
 </pre></pre><p><br/><i>Sample:</i></p><pre class="sample"><pre>CREATE KEYSPACE Excelsior
            WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3};
 
@@ -101,7 +101,7 @@ CREATE TABLE timeline (
 INSERT INTO test(pk, t, v, s) VALUES (0, 0, 'val0', 'static0');
 INSERT INTO test(pk, t, v, s) VALUES (0, 1, 'val1', 'static1');
 SELECT * FROM test WHERE pk=0 AND t=0;
-</pre></pre><p>the last query will return <code>'static1'</code> as value for <code>s</code>, since <code>s</code> is static and thus the 2nd insertion modified this &#8220;shared&#8221; value. Note however that static columns are only static within a given partition, and if in the example above both rows where from different partitions (i.e. if they had different value for <code>pk</code>), then the 2nd insertion would not have modified the value of <code>s</code> for the first row.</p><p>A few restrictions applies to when static columns are allowed:</p><ul><li>tables with the <code>COMPACT STORAGE</code> option (see below) cannot have them</li><li>a table without clustering columns cannot have static columns (in a table without clustering columns, every partition has only one row, and so every column is inherently static).</li><li>only non <code>PRIMARY KEY</code> columns can be static</li></ul><h4 id="createTableOptions"><code>&lt;option></code></h4><p>The <code>CREATE TABLE</cod
 e> statement supports a number of options that controls the configuration of a new table. These options can be specified after the <code>WITH</code> keyword.</p><p>The first of these option is <code>COMPACT STORAGE</code>. This option is mainly targeted towards backward compatibility for definitions created before CQL3 (see <a href="http://www.datastax.com/dev/blog/thrift-to-cql3">www.datastax.com/dev/blog/thrift-to-cql3</a> for more details).  The option also provides a slightly more compact layout of data on disk but at the price of diminished flexibility and extensibility for the table.  Most notably, <code>COMPACT STORAGE</code> tables cannot have collections nor static columns and a <code>COMPACT STORAGE</code> table with at least one clustering column supports exactly one (as in not 0 nor more than 1) column not part of the <code>PRIMARY KEY</code> definition (which imply in particular that you cannot add nor remove columns after creation). For those reasons, <code>COMPACT STO
 RAGE</code> is not recommended outside of the backward compatibility reason evoked above.</p><p>Another option is <code>CLUSTERING ORDER</code>. It allows to define the ordering of rows on disk. It takes the list of the clustering column names with, for each of them, the on-disk order (Ascending or descending). Note that this option affects <a href="#selectOrderBy">what <code>ORDER BY</code> are allowed during <code>SELECT</code></a>.</p><p>Table creation supports the following other <code>&lt;property></code>:</p><table><tr><th>option                    </th><th>kind   </th><th>default   </th><th>description</th></tr><tr><td><code>comment</code>                    </td><td><em>simple</em> </td><td>none        </td><td>A free-form, human-readable comment.</td></tr><tr><td><code>read_repair_chance</code>         </td><td><em>simple</em> </td><td>0.1         </td><td>The probability with which to query extra nodes (e.g. more nodes than required by the consistency level) for the purpos
 e of read repairs.</td></tr><tr><td><code>dclocal_read_repair_chance</code> </td><td><em>simple</em> </td><td>0           </td><td>The probability with which to query extra nodes (e.g. more nodes than required by the consistency level) belonging to the same data center than the read coordinator for the purpose of read repairs.</td></tr><tr><td><code>gc_grace_seconds</code>           </td><td><em>simple</em> </td><td>864000      </td><td>Time to wait before garbage collecting tombstones (deletion markers).</td></tr><tr><td><code>bloom_filter_fp_chance</code>     </td><td><em>simple</em> </td><td>0.00075     </td><td>The target probability of false positive of the sstable bloom filters. Said bloom filters will be sized to provide the provided probability (thus lowering this value impact the size of bloom filters in-memory and on-disk)</td></tr><tr><td><code>compaction</code>                 </td><td><em>map</em>    </td><td><em>see below</em> </td><td>The compaction options to use, se
 e below.</td></tr><tr><td><code>compression</code>                </td><td><em>map</em>    </td><td><em>see below</em> </td><td>Compression options, see below. </td></tr><tr><td><code>replicate_on_write</code>         </td><td><em>simple</em> </td><td>true        </td><td>Whether to replicate data on write. This can only be set to false for tables with counters values. Disabling this is dangerous and can result in random lose of counters, don&#8217;t disable unless you are sure to know what you are doing</td></tr><tr><td><code>caching</code>                    </td><td><em>simple</em> </td><td>keys_only   </td><td>Whether to cache keys (&#8220;key cache&#8221;) and/or rows (&#8220;row cache&#8221;) for this table. Valid values are: <code>all</code>, <code>keys_only</code>, <code>rows_only</code> and <code>none</code>. </td></tr></table><h4 id="compactionOptions"><code>compaction</code> options</h4><p>The <code>compaction</code> property must at least define the <code>'class'</code> 
 sub-option, that defines the compaction strategy class to use. The default supported class are <code>'SizeTieredCompactionStrategy'</code> and <code>'LeveledCompactionStrategy'</code>. Custom strategy can be provided by specifying the full class name as a <a href="#constants">string constant</a>. The rest of the sub-options depends on the chosen class. The sub-options supported by the default classes are:</p><table><tr><th>option                         </th><th>supported compaction strategy </th><th>default </th><th>description </th></tr><tr><td><code>enabled</code>                        </td><td><em>all</em>                           </td><td>true      </td><td>A boolean denoting whether compaction should be enabled or not.</td></tr><tr><td><code>tombstone_threshold</code>            </td><td><em>all</em>                           </td><td>0.2       </td><td>A ratio such that if a sstable has more than this ratio of gcable tombstones over all contained columns, the sstable will b
 e compacted (with no other sstables) for the purpose of purging those tombstones. </td></tr><tr><td><code>tombstone_compaction_interval</code>  </td><td><em>all</em>                           </td><td>1 day     </td><td>The minimum time to wait after an sstable creation time before considering it for &#8220;tombstone compaction&#8221;, where &#8220;tombstone compaction&#8221; is the compaction triggered if the sstable has more gcable tombstones than <code>tombstone_threshold</code>. </td></tr><tr><td><code>unchecked_tombstone_compaction</code> </td><td><em>all</em>                           </td><td>false    </td><td>Setting this to true enables more aggressive tombstone compactions &#8211; single sstable tombstone compactions will run without checking how likely it is that they will be successful. </td></tr><tr><td><code>min_sstable_size</code>               </td><td>SizeTieredCompactionStrategy    </td><td>50MB      </td><td>The size tiered strategy groups SSTables to compact in b
 uckets. A bucket groups SSTables that differs from less than 50% in size.  However, for small sizes, this would result in a bucketing that is too fine grained. <code>min_sstable_size</code> defines a size threshold (in bytes) below which all SSTables belong to one unique bucket</td></tr><tr><td><code>min_threshold</code>                  </td><td>SizeTieredCompactionStrategy    </td><td>4         </td><td>Minimum number of SSTables needed to start a minor compaction.</td></tr><tr><td><code>max_threshold</code>                  </td><td>SizeTieredCompactionStrategy    </td><td>32        </td><td>Maximum number of SSTables processed by one minor compaction.</td></tr><tr><td><code>bucket_low</code>                     </td><td>SizeTieredCompactionStrategy    </td><td>0.5       </td><td>Size tiered consider sstables to be within the same bucket if their size is within [average_size * <code>bucket_low</code>, average_size * <code>bucket_high</code> ] (i.e the default groups sstable whose
  sizes diverges by at most 50%)</td></tr><tr><td><code>bucket_high</code>                    </td><td>SizeTieredCompactionStrategy    </td><td>1.5       </td><td>Size tiered consider sstables to be within the same bucket if their size is within [average_size * <code>bucket_low</code>, average_size * <code>bucket_high</code> ] (i.e the default groups sstable whose sizes diverges by at most 50%).</td></tr><tr><td><code>sstable_size_in_mb</code>             </td><td>LeveledCompactionStrategy       </td><td>5MB       </td><td>The target size (in MB) for sstables in the leveled strategy. Note that while sstable sizes should stay less or equal to <code>sstable_size_in_mb</code>, it is possible to exceptionally have a larger sstable as during compaction, data for a given partition key are never split into 2 sstables</td></tr></table><p>For the <code>compression</code> property, the following default sub-options are available:</p><table><tr><th>option              </th><th>default        </
 th><th>description </th></tr><tr><td><code>sstable_compression</code> </td><td>LZ4Compressor    </td><td>The compression algorithm to use. Default compressor are: LZ4Compressor, SnappyCompressor and DeflateCompressor. Use an empty string (<code>''</code>) to disable compression. Custom compressor can be provided by specifying the full class name as a <a href="#constants">string constant</a>.</td></tr><tr><td><code>chunk_length_kb</code>     </td><td>64KB             </td><td>On disk SSTables are compressed by block (to allow random reads). This defines the size (in KB) of said block. Bigger values may improve the compression rate, but increases the minimum size of data to be read from disk for a read </td></tr><tr><td><code>crc_check_chance</code>    </td><td>1.0              </td><td>When compression is enabled, each compressed block includes a checksum of that block for the purpose of detecting disk bitrot and avoiding the propagation of corruption to other replica. This option de
 fines the probability with which those checksums are checked during read. By default they are always checked. Set to 0 to disable checksum checking and to 0.5 for instance to check them every other read</td></tr></table><h4 id="Otherconsiderations">Other considerations:</h4><ul><li>When <a href="#insertStmt/&quot;updating&quot;:#updateStmt">inserting</a> a given row, not all columns needs to be defined (except for those part of the key), and missing columns occupy no space on disk. Furthermore, adding new columns (see &lt;a href=#alterStmt><tt>ALTER TABLE</tt></a>) is a constant time operation. There is thus no need to try to anticipate future usage (or to cry when you haven&#8217;t) when creating a table.</li></ul><h3 id="alterTableStmt">ALTER TABLE</h3><p><i>Syntax:</i></p><pre class="syntax"><pre>&lt;alter-table-stmt> ::= ALTER (TABLE | COLUMNFAMILY) &lt;tablename> &lt;instruction>
+</pre></pre><p>the last query will return <code>'static1'</code> as value for <code>s</code>, since <code>s</code> is static and thus the 2nd insertion modified this &#8220;shared&#8221; value. Note however that static columns are only static within a given partition, and if in the example above both rows where from different partitions (i.e. if they had different value for <code>pk</code>), then the 2nd insertion would not have modified the value of <code>s</code> for the first row.</p><p>A few restrictions applies to when static columns are allowed:</p><ul><li>tables with the <code>COMPACT STORAGE</code> option (see below) cannot have them</li><li>a table without clustering columns cannot have static columns (in a table without clustering columns, every partition has only one row, and so every column is inherently static).</li><li>only non <code>PRIMARY KEY</code> columns can be static</li></ul><h4 id="createTableOptions"><code>&lt;option></code></h4><p>The <code>CREATE TABLE</cod
 e> statement supports a number of options that controls the configuration of a new table. These options can be specified after the <code>WITH</code> keyword.</p><p>The first of these option is <code>COMPACT STORAGE</code>. This option is mainly targeted towards backward compatibility for definitions created before CQL3 (see <a href="http://www.datastax.com/dev/blog/thrift-to-cql3">www.datastax.com/dev/blog/thrift-to-cql3</a> for more details).  The option also provides a slightly more compact layout of data on disk but at the price of diminished flexibility and extensibility for the table.  Most notably, <code>COMPACT STORAGE</code> tables cannot have collections nor static columns and a <code>COMPACT STORAGE</code> table with at least one clustering column supports exactly one (as in not 0 nor more than 1) column not part of the <code>PRIMARY KEY</code> definition (which imply in particular that you cannot add nor remove columns after creation). For those reasons, <code>COMPACT STO
 RAGE</code> is not recommended outside of the backward compatibility reason evoked above.</p><p>Another option is <code>CLUSTERING ORDER</code>. It allows to define the ordering of rows on disk. It takes the list of the clustering column names with, for each of them, the on-disk order (Ascending or descending). Note that this option affects <a href="#selectOrderBy">what <code>ORDER BY</code> are allowed during <code>SELECT</code></a>.</p><p>Table creation supports the following other <code>&lt;property></code>:</p><table><tr><th>option                    </th><th>kind   </th><th>default   </th><th>description</th></tr><tr><td><code>comment</code>                    </td><td><em>simple</em> </td><td>none        </td><td>A free-form, human-readable comment.</td></tr><tr><td><code>read_repair_chance</code>         </td><td><em>simple</em> </td><td>0.1         </td><td>The probability with which to query extra nodes (e.g. more nodes than required by the consistency level) for the purpos
 e of read repairs.</td></tr><tr><td><code>dclocal_read_repair_chance</code> </td><td><em>simple</em> </td><td>0           </td><td>The probability with which to query extra nodes (e.g. more nodes than required by the consistency level) belonging to the same data center than the read coordinator for the purpose of read repairs.</td></tr><tr><td><code>gc_grace_seconds</code>           </td><td><em>simple</em> </td><td>864000      </td><td>Time to wait before garbage collecting tombstones (deletion markers).</td></tr><tr><td><code>bloom_filter_fp_chance</code>     </td><td><em>simple</em> </td><td>0.00075     </td><td>The target probability of false positive of the sstable bloom filters. Said bloom filters will be sized to provide the provided probability (thus lowering this value impact the size of bloom filters in-memory and on-disk)</td></tr><tr><td><code>compaction</code>                 </td><td><em>map</em>    </td><td><em>see below</em> </td><td>The compaction options to use, se
 e below.</td></tr><tr><td><code>compression</code>                </td><td><em>map</em>    </td><td><em>see below</em> </td><td>Compression options, see below. </td></tr><tr><td><code>replicate_on_write</code>         </td><td><em>simple</em> </td><td>true        </td><td>Whether to replicate data on write. This can only be set to false for tables with counters values. Disabling this is dangerous and can result in random lose of counters, don&#8217;t disable unless you are sure to know what you are doing</td></tr><tr><td><code>caching</code>                    </td><td><em>simple</em> </td><td>keys_only   </td><td>Whether to cache keys (&#8220;key cache&#8221;) and/or rows (&#8220;row cache&#8221;) for this table. Valid values are: <code>all</code>, <code>keys_only</code>, <code>rows_only</code> and <code>none</code>. </td></tr><tr><td><code>default_time_to_live</code>       </td><td><em>simple</em> </td><td>0           </td><td>The default expiration time (&#8220;TTL&#8221;) in sec
 onds for a table.</td></tr></table><h4 id="compactionOptions"><code>compaction</code> options</h4><p>The <code>compaction</code> property must at least define the <code>'class'</code> sub-option, that defines the compaction strategy class to use. The default supported class are <code>'SizeTieredCompactionStrategy'</code> and <code>'LeveledCompactionStrategy'</code>. Custom strategy can be provided by specifying the full class name as a <a href="#constants">string constant</a>. The rest of the sub-options depends on the chosen class. The sub-options supported by the default classes are:</p><table><tr><th>option                         </th><th>supported compaction strategy </th><th>default </th><th>description </th></tr><tr><td><code>enabled</code>                        </td><td><em>all</em>                           </td><td>true      </td><td>A boolean denoting whether compaction should be enabled or not.</td></tr><tr><td><code>tombstone_threshold</code>            </td><td><em>al
 l</em>                           </td><td>0.2       </td><td>A ratio such that if a sstable has more than this ratio of gcable tombstones over all contained columns, the sstable will be compacted (with no other sstables) for the purpose of purging those tombstones. </td></tr><tr><td><code>tombstone_compaction_interval</code>  </td><td><em>all</em>                           </td><td>1 day     </td><td>The minimum time to wait after an sstable creation time before considering it for &#8220;tombstone compaction&#8221;, where &#8220;tombstone compaction&#8221; is the compaction triggered if the sstable has more gcable tombstones than <code>tombstone_threshold</code>. </td></tr><tr><td><code>unchecked_tombstone_compaction</code> </td><td><em>all</em>                           </td><td>false    </td><td>Setting this to true enables more aggressive tombstone compactions &#8211; single sstable tombstone compactions will run without checking how likely it is that they will be successful. </t
 d></tr><tr><td><code>min_sstable_size</code>               </td><td>SizeTieredCompactionStrategy    </td><td>50MB      </td><td>The size tiered strategy groups SSTables to compact in buckets. A bucket groups SSTables that differs from less than 50% in size.  However, for small sizes, this would result in a bucketing that is too fine grained. <code>min_sstable_size</code> defines a size threshold (in bytes) below which all SSTables belong to one unique bucket</td></tr><tr><td><code>min_threshold</code>                  </td><td>SizeTieredCompactionStrategy    </td><td>4         </td><td>Minimum number of SSTables needed to start a minor compaction.</td></tr><tr><td><code>max_threshold</code>                  </td><td>SizeTieredCompactionStrategy    </td><td>32        </td><td>Maximum number of SSTables processed by one minor compaction.</td></tr><tr><td><code>bucket_low</code>                     </td><td>SizeTieredCompactionStrategy    </td><td>0.5       </td><td>Size tiered conside
 r sstables to be within the same bucket if their size is within [average_size * <code>bucket_low</code>, average_size * <code>bucket_high</code> ] (i.e the default groups sstable whose sizes diverges by at most 50%)</td></tr><tr><td><code>bucket_high</code>                    </td><td>SizeTieredCompactionStrategy    </td><td>1.5       </td><td>Size tiered consider sstables to be within the same bucket if their size is within [average_size * <code>bucket_low</code>, average_size * <code>bucket_high</code> ] (i.e the default groups sstable whose sizes diverges by at most 50%).</td></tr><tr><td><code>sstable_size_in_mb</code>             </td><td>LeveledCompactionStrategy       </td><td>5MB       </td><td>The target size (in MB) for sstables in the leveled strategy. Note that while sstable sizes should stay less or equal to <code>sstable_size_in_mb</code>, it is possible to exceptionally have a larger sstable as during compaction, data for a given partition key are never split into 2 s
 stables</td></tr></table><p>For the <code>compression</code> property, the following default sub-options are available:</p><table><tr><th>option              </th><th>default        </th><th>description </th></tr><tr><td><code>sstable_compression</code> </td><td>LZ4Compressor    </td><td>The compression algorithm to use. Default compressor are: LZ4Compressor, SnappyCompressor and DeflateCompressor. Use an empty string (<code>''</code>) to disable compression. Custom compressor can be provided by specifying the full class name as a <a href="#constants">string constant</a>.</td></tr><tr><td><code>chunk_length_kb</code>     </td><td>64KB             </td><td>On disk SSTables are compressed by block (to allow random reads). This defines the size (in KB) of said block. Bigger values may improve the compression rate, but increases the minimum size of data to be read from disk for a read </td></tr><tr><td><code>crc_check_chance</code>    </td><td>1.0              </td><td>When compression 
 is enabled, each compressed block includes a checksum of that block for the purpose of detecting disk bitrot and avoiding the propagation of corruption to other replica. This option defines the probability with which those checksums are checked during read. By default they are always checked. Set to 0 to disable checksum checking and to 0.5 for instance to check them every other read</td></tr></table><h4 id="Otherconsiderations">Other considerations:</h4><ul><li>When <a href="#insertStmt/&quot;updating&quot;:#updateStmt">inserting</a> a given row, not all columns needs to be defined (except for those part of the key), and missing columns occupy no space on disk. Furthermore, adding new columns (see &lt;a href=#alterStmt><tt>ALTER TABLE</tt></a>) is a constant time operation. There is thus no need to try to anticipate future usage (or to cry when you haven&#8217;t) when creating a table.</li></ul><h3 id="alterTableStmt">ALTER TABLE</h3><p><i>Syntax:</i></p><pre class="syntax"><pre>&l
 t;alter-table-stmt> ::= ALTER (TABLE | COLUMNFAMILY) &lt;tablename> &lt;instruction>
 
 &lt;instruction> ::= ALTER &lt;identifier> TYPE &lt;type>
                 | ADD   &lt;identifier> &lt;type>
@@ -171,7 +171,7 @@ SET director = 'Joss Whedon',
 WHERE movie = 'Serenity';
 
 UPDATE UserActions SET total = total + 2 WHERE user = B70DE1D0-9908-4AE3-BE34-5573E5B09F14 AND action = 'click';
-</pre></pre><p><br/>The <code>UPDATE</code> statement writes one or more columns for a given row in a table. The <code>&lt;where-clause></code> is used to select the row to update and must include all columns composing the <code>PRIMARY KEY</code> (the <code>IN</code> relation is only supported for the last column of the partition key). Other columns values are specified through <code>&lt;assignment></code> after the <code>SET</code> keyword.</p><p>Note that unlike in SQL, <code>UPDATE</code> does not check the prior existence of the row by default: the row is created if none existed before, and updated otherwise. Furthermore, there is no mean to know which of creation or update happened.</p><p>It is however possible to use the conditions on some columns through <code>IF</code>, in which case the row will not be updated unless such condition are met. But please note that using <code>IF</code> conditions will incur a non negligible performance cost (internally, Paxos will be used) so
  this should be used sparingly.</p><p>In an <code>UPDATE</code> statement, all updates within the same partition key are applied atomically and in isolation.</p><p>The <code>c = c + 3</code> form of <code>&lt;assignment></code> is used to increment/decrement counters. The identifier after the &#8216;=&#8217; sign <strong>must</strong> be the same than the one before the &#8216;=&#8217; sign (Only increment/decrement is supported on counters, not the assignment of a specific value).</p><p>The <code>id = id + &lt;collection-literal></code> and <code>id[value1] = value2</code> forms of <code>&lt;assignment></code> are for collections. Please refer to the <a href="#collections">relevant section</a> for more details.</p><h4 id="updateOptions"><code>&lt;options></code></h4><p>The <code>UPDATE</code> and <code>INSERT</code> statements allows to specify the following options for the insertion:</p><ul><li><code>TIMESTAMP</code>: sets the timestamp for the operation. If not specified, the cur
 rent time of the insertion (in microseconds) is used. This is usually a suitable default.</li><li><code>TTL</code>: allows to specify an optional Time To Live (in seconds) for the inserted values. If set, the inserted values are automatically removed from the database after the specified time. Note that the TTL concerns the inserted values, not the column themselves. This means that any subsequent update of the column will also reset the TTL (to whatever TTL is specified in that update). By default, values never expire. A TTL of 0 or a negative one is equivalent to no TTL.</li></ul><h3 id="deleteStmt">DELETE</h3><p><i>Syntax:</i></p><pre class="syntax"><pre>&lt;delete-stmt> ::= DELETE ( &lt;selection> ( ',' &lt;selection> )* )?
+</pre></pre><p><br/>The <code>UPDATE</code> statement writes one or more columns for a given row in a table. The <code>&lt;where-clause></code> is used to select the row to update and must include all columns composing the <code>PRIMARY KEY</code> (the <code>IN</code> relation is only supported for the last column of the partition key). Other columns values are specified through <code>&lt;assignment></code> after the <code>SET</code> keyword.</p><p>Note that unlike in SQL, <code>UPDATE</code> does not check the prior existence of the row by default: the row is created if none existed before, and updated otherwise. Furthermore, there is no mean to know which of creation or update happened.</p><p>It is however possible to use the conditions on some columns through <code>IF</code>, in which case the row will not be updated unless such condition are met. But please note that using <code>IF</code> conditions will incur a non negligible performance cost (internally, Paxos will be used) so
  this should be used sparingly.</p><p>In an <code>UPDATE</code> statement, all updates within the same partition key are applied atomically and in isolation.</p><p>The <code>c = c + 3</code> form of <code>&lt;assignment></code> is used to increment/decrement counters. The identifier after the &#8216;=&#8217; sign <strong>must</strong> be the same than the one before the &#8216;=&#8217; sign (Only increment/decrement is supported on counters, not the assignment of a specific value).</p><p>The <code>id = id + &lt;collection-literal></code> and <code>id[value1] = value2</code> forms of <code>&lt;assignment></code> are for collections. Please refer to the <a href="#collections">relevant section</a> for more details.</p><h4 id="updateOptions"><code>&lt;options></code></h4><p>The <code>UPDATE</code> and <code>INSERT</code> statements allows to specify the following options for the insertion:</p><ul><li><code>TIMESTAMP</code>: sets the timestamp for the operation. If not specified, the coo
 rdinator will use the current time (in microseconds) at the start of statement execution as the timestamp. This is usually a suitable default.</li><li><code>TTL</code>: allows to specify an optional Time To Live (in seconds) for the inserted values. If set, the inserted values are automatically removed from the database after the specified time. Note that the TTL concerns the inserted values, not the column themselves. This means that any subsequent update of the column will also reset the TTL (to whatever TTL is specified in that update). By default, values never expire. A TTL of 0 or a negative one is equivalent to no TTL.</li></ul><h3 id="deleteStmt">DELETE</h3><p><i>Syntax:</i></p><pre class="syntax"><pre>&lt;delete-stmt> ::= DELETE ( &lt;selection> ( ',' &lt;selection> )* )?
                   FROM &lt;tablename>
                   ( USING TIMESTAMP &lt;integer>)?
                   WHERE &lt;where-clause>

Modified: cassandra/site/publish/doc/cql3/CQL-2.1.html
URL: http://svn.apache.org/viewvc/cassandra/site/publish/doc/cql3/CQL-2.1.html?rev=1663774&r1=1663773&r2=1663774&view=diff
==============================================================================
--- cassandra/site/publish/doc/cql3/CQL-2.1.html (original)
+++ cassandra/site/publish/doc/cql3/CQL-2.1.html Tue Mar  3 20:05:46 2015
@@ -38,7 +38,7 @@
 
   &lt;properties> ::= &lt;property> (AND &lt;property>)*
     &lt;property> ::= &lt;identifier> '=' ( &lt;identifier> | &lt;constant> | &lt;map-literal> )
-</pre></pre><p><br/>Please note that not every possible productions of the grammar above will be valid in practice. Most notably, <code>&lt;variable></code> and nested <code>&lt;collection-literal></code> are currently not allowed inside <code>&lt;collection-literal></code>.</p><p>A <code>&lt;variable></code> can be either anonymous (a question mark (<code>?</code>)) or named (an identifier preceded by <code>:</code>). Both declare a bind variables for <a href="#preparedStatement">prepared statements</a>. The only difference between an anymous and a named variable is that a named one will be easier to refer to (how exactly depends on the client driver used).</p><p>The <code>&lt;properties></code> production is use by statement that create and alter keyspaces and tables. Each <code>&lt;property></code> is either a <em>simple</em> one, in which case it just has a value, or a <em>map</em> one, in which case it&#8217;s value is a map grouping sub-options. The following will refer to one
  or the other as the <em>kind</em> (<em>simple</em> or <em>map</em>) of the property.</p><p>A <code>&lt;tablename></code> will be used to identify a table. This is an identifier representing the table name that can be preceded by a keyspace name. The keyspace name, if provided, allow to identify a table in another keyspace than the currently active one (the currently active keyspace is set through the <a href="#useStmt"><tt>USE</tt></a> statement).</p><p>For supported <code>&lt;function></code>, see the section on <a href="#functions">functions</a>.</p><h3 id="preparedStatement">Prepared Statement</h3><p>CQL supports <em>prepared statements</em>. Prepared statement is an optimization that allows to parse a query only once but execute it multiple times with different concrete values.</p><p>In a statement, each time a column value is expected (in the data manipulation and query statements), a <code>&lt;variable></code> (see above) can be used instead. A statement with bind variables m
 ust then be <em>prepared</em>. Once it has been prepared, it can executed by providing concrete values for the bind variables. The exact procedure to prepare a statement and execute a prepared statement depends on the CQL driver used and is beyond the scope of this document.</p><h2 id="dataDefinition">Data Definition</h2><h3 id="createKeyspaceStmt">CREATE KEYSPACE</h3><p><i>Syntax:</i></p><pre class="syntax"><pre>&lt;create-keyspace-stmt> ::= CREATE KEYSPACE (IF NOT EXISTS)? &lt;identifier> WITH &lt;properties>
+</pre></pre><p><br/>Please note that not every possible productions of the grammar above will be valid in practice. Most notably, <code>&lt;variable></code> and nested <code>&lt;collection-literal></code> are currently not allowed inside <code>&lt;collection-literal></code>.</p><p>A <code>&lt;variable></code> can be either anonymous (a question mark (<code>?</code>)) or named (an identifier preceded by <code>:</code>). Both declare a bind variables for <a href="#preparedStatement">prepared statements</a>. The only difference between an anymous and a named variable is that a named one will be easier to refer to (how exactly depends on the client driver used).</p><p>The <code>&lt;properties></code> production is use by statement that create and alter keyspaces and tables. Each <code>&lt;property></code> is either a <em>simple</em> one, in which case it just has a value, or a <em>map</em> one, in which case it&#8217;s value is a map grouping sub-options. The following will refer to one
  or the other as the <em>kind</em> (<em>simple</em> or <em>map</em>) of the property.</p><p>A <code>&lt;tablename></code> will be used to identify a table. This is an identifier representing the table name that can be preceded by a keyspace name. The keyspace name, if provided, allow to identify a table in another keyspace than the currently active one (the currently active keyspace is set through the <a href="#useStmt"><tt>USE</tt></a> statement).</p><p>For supported <code>&lt;function></code>, see the section on <a href="#functions">functions</a>.</p><h3 id="preparedStatement">Prepared Statement</h3><p>CQL supports <em>prepared statements</em>. Prepared statement is an optimization that allows to parse a query only once but execute it multiple times with different concrete values.</p><p>In a statement, each time a column value is expected (in the data manipulation and query statements), a <code>&lt;variable></code> (see above) can be used instead. A statement with bind variables m
 ust then be <em>prepared</em>. Once it has been prepared, it can executed by providing concrete values for the bind variables. The exact procedure to prepare a statement and execute a prepared statement depends on the CQL driver used and is beyond the scope of this document.</p><p>In addition to providing column values, bind markers may be used to provide values for <code>LIMIT</code>, <code>TIMESTAMP</code>, and <code>TTL</code> clauses.  If anonymous bind markers are used, the names for the query parameters will be <code>[limit]</code>, <code>[timestamp]</code>, and <code>[ttl]</code>, respectively.</p><h2 id="dataDefinition">Data Definition</h2><h3 id="createKeyspaceStmt">CREATE KEYSPACE</h3><p><i>Syntax:</i></p><pre class="syntax"><pre>&lt;create-keyspace-stmt> ::= CREATE KEYSPACE (IF NOT EXISTS)? &lt;identifier> WITH &lt;properties>
 </pre></pre><p><br/><i>Sample:</i></p><pre class="sample"><pre>CREATE KEYSPACE Excelsior
            WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3};
 



Mime
View raw message