Author: slebresne
Date: Wed Jan 9 16:04:33 2013
New Revision: 1430925
URL: http://svn.apache.org/viewvc?rev=1430925&view=rev
Log:
Fix CQL3 ref doc on website
Modified:
cassandra/site/publish/doc/cql3/CQL.html
Modified: cassandra/site/publish/doc/cql3/CQL.html
URL:
http://svn.apache.org/viewvc/cassandra/site/publish/doc/cql3/CQL.html?rev=1430925&r1=1430924&r2=1430925&view=diff
==============================================================================
--- cassandra/site/publish/doc/cql3/CQL.html (original)
+++ cassandra/site/publish/doc/cql3/CQL.html Wed Jan 9 16:04:33 2013
@@ -87,7 +87,7 @@ CREATE TABLE timeline (
other text,
PRIMARY KEY (k)
)
-</pre></pre><p>Moreover, a table must define at least one column that is not
part of the PRIMARY KEY as a row exists in Cassandra only if it contains at
least one value for one such column.</p><h4
id="createTablepartitionClustering">Partition key and clustering</h4><p>In CQL,
the order in which columns are defined for the <code>PRIMARY KEY</code>
matters. The first column of the key is called the <i>partition key</i>. It has
the property that all the rows sharing the same partition key (even across
table in fact) are stored on the same physical node. Also,
insertion/update/deletion on rows sharing the same partition key for a given
table are performed <i>atomically</i> and in <i>isolation</i>. Note that it is
possible to have a composite partition key, i.e. a partition key formed of
multiple columns, using an extra set of parentheses to define which columns
forms the partition key.</p><p>The remaining columns of the <code>PRIMARY
KEY</code> definition, if any, are called <i>
clustering keys</i>. On a given physical node, rows for a given partition key
are stored in the order induced by the clustering keys, making the retrieval of
rows in that clustering order particularly efficient (see <a
href="#selectStmt"><tt>SELECT</tt></a>).</p><h4
id="createTableOptions"><code><option></code></h4><p>The <code>CREATE
TABLE</code> 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 meanly targeted towards backward compatibility
with some table definition created before CQL3. But it also provides a
slightly more compact layout of data on disk, though at the price of
flexibility and extensibility, and for that reason is not recommended unless
for the backward compatibility reason. The restriction for table with
<code>COMPACT STORAGE</code> is that they support one and only one
column outside of the ones part of the <code>PRIMARY KEY</code>. It also
follows that columns cannot be added nor removed after creation. A table with
<code>COMPACT STORAGE</code> must also define at least one <a
href="createTablepartitionClustering">clustering key</a>.</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 key 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><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</c
ode> </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 purpose 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
si
ze 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
otpions to use, see 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’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
(“key cache”) and/or rows (“row cache”) 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>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 sstabl
e 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
mininum time to wait after an sstable creation time before considering it for
“tombstone compaction”, where “tombstone compaction” is
the compaction triggered if the sstable has more gcable tombstones than
<code>tombstone_threshold</code>.
</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 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_co
mpaction_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_compaction_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 * <co
de>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>SnappyCompressor </td><td>The compression algorithm to use. Default
compressor are: SnappyCompressor and DeflateCompressor. Use an empty string
(<code>''</code>) to disable compression. Custom compressor can be provide
d 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="#insert
Stmt/"updating":#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 <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’t) when creating a table.</li></ul><h3 id="alterTableStmt">ALTER
TABLE</h3><p><i>Syntax:</i></p><pre class="syntax"><pre><alter-table-stmt>
::= ALTER (TABLE | COLUMNFAMILY) <tablename> <instruction>
+</pre></pre><p>Moreover, a table must define at least one column that is not
part of the PRIMARY KEY as a row exists in Cassandra only if it contains at
least one value for one such column.</p><h4
id="createTablepartitionClustering">Partition key and clustering</h4><p>In CQL,
the order in which columns are defined for the <code>PRIMARY KEY</code>
matters. The first column of the key is called the <i>partition key</i>. It has
the property that all the rows sharing the same partition key (even across
table in fact) are stored on the same physical node. Also,
insertion/update/deletion on rows sharing the same partition key for a given
table are performed <i>atomically</i> and in <i>isolation</i>. Note that it is
possible to have a composite partition key, i.e. a partition key formed of
multiple columns, using an extra set of parentheses to define which columns
forms the partition key.</p><p>The remaining columns of the <code>PRIMARY
KEY</code> definition, if any, are called <i>
clustering keys</i>. On a given physical node, rows for a given partition key
are stored in the order induced by the clustering keys, making the retrieval of
rows in that clustering order particularly efficient (see <a
href="#selectStmt"><tt>SELECT</tt></a>).</p><h4
id="createTableOptions"><code><option></code></h4><p>The <code>CREATE
TABLE</code> 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 meanly targeted towards backward compatibility
with some table definition created before CQL3. But it also provides a
slightly more compact layout of data on disk, though at the price of
flexibility and extensibility, and for that reason is not recommended unless
for the backward compatibility reason. The restriction for table with
<code>COMPACT STORAGE</code> is that they support one and only one
column outside of the ones part of the <code>PRIMARY KEY</code>. It also
follows that columns cannot be added nor removed after creation. A table with
<code>COMPACT STORAGE</code> must also define at least one <a
href="createTablepartitionClustering">clustering key</a>.</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 key 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><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</c
ode> </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 purpose 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
si
ze 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
otpions to use, see 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’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
(“key cache”) and/or rows (“row cache”) 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>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 sstabl
e 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
mininum time to wait after an sstable creation time before considering it for
“tombstone compaction”, where “tombstone compaction” is
the compaction triggered if the sstable has more gcable tombstones than
<code>tombstone_threshold</code>.
</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 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_th
reshold</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 * <co
de>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>SnappyCompressor </td><td>The compression algorithm to use. Default
compressor are: SnappyCompressor and DeflateCompressor. Use an empty string
(<code>''</code>) to disable compression. Custom compressor can be provide
d 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="#insert
Stmt/"updating":#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 <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’t) when creating a table.</li></ul><h3 id="alterTableStmt">ALTER
TABLE</h3><p><i>Syntax:</i></p><pre class="syntax"><pre><alter-table-stmt>
::= ALTER (TABLE | COLUMNFAMILY) <tablename> <instruction>
<instruction> ::= ALTER <identifier> TYPE <type>
| ADD <identifier> <type>
