{% trans %}Main documentation parts:{% endtrans %}
+|
+ {% trans %}Getting started{% endtrans %} {% trans %}Cassandra Architecture{% endtrans %} {% trans %}Data Modeling{% endtrans %} {% trans %}Cassandra Query Language{% endtrans %} {% trans %}Configuration{% endtrans %} |
+ {% trans %}Operating Cassandra{% endtrans %} {% trans %}Cassandra's Tools{% endtrans %} {% trans %}Troubleshooting{% endtrans %} {% trans %}FAQs{% endtrans %} |
{% trans %}Meta informations:{% endtrans %}
+ +{% trans %}Reporting bugs{% endtrans %}
+{% trans %}Contact us{% endtrans %}
+ +{% endblock %} diff --git a/doc/source/architecture.rst b/doc/source/architecture/dynamo.rst similarity index 72% rename from doc/source/architecture.rst rename to doc/source/architecture/dynamo.rst index 920941440f..d146471eb2 100644 --- a/doc/source/architecture.rst +++ b/doc/source/architecture/dynamo.rst @@ -14,14 +14,6 @@ .. See the License for the specific language governing permissions and .. limitations under the License. -Architecture -============ - -Overview --------- - -.. todo:: todo - Dynamo ------ @@ -143,75 +135,3 @@ still useful guarantee: reads are guaranteed to see the latest write from within If this type of strong consistency isn't required, lower consistency levels like ``ONE`` may be used to improve throughput, latency, and availability. - -Storage Engine --------------- - -.. _commit-log: - -CommitLog -^^^^^^^^^ - -.. todo:: todo - -.. _memtables: - -Memtables -^^^^^^^^^ - -Memtables are in-memory structures where Cassandra buffers writes. In general, there is one active memtable per table. -Eventually, memtables are flushed onto disk and become immutable `SSTables`_. This can be triggered in several -ways: - -- The memory usage of the memtables exceeds the configured threshold (see ``memtable_cleanup_threshold``) -- The :ref:`commit-log` approaches its maximum size, and forces memtable flushes in order to allow commitlog segments to - be freed - -Memtables may be stored entirely on-heap or partially off-heap, depending on ``memtable_allocation_type``. - -SSTables -^^^^^^^^ - -SSTables are the immutable data files that Cassandra uses for persisting data on disk. - -As SSTables are flushed to disk from :ref:`memtables` or are streamed from other nodes, Cassandra triggers compactions -which combine multiple SSTables into one. Once the new SSTable has been written, the old SSTables can be removed. - -Each SSTable is comprised of multiple components stored in separate files: - -``Data.db`` - The actual data, i.e. the contents of rows. - -``Index.db`` - An index from partition keys to positions in the ``Data.db`` file. For wide partitions, this may also include an - index to rows within a partition. - -``Summary.db`` - A sampling of (by default) every 128th entry in the ``Index.db`` file. - -``Filter.db`` - A Bloom Filter of the partition keys in the SSTable. - -``CompressionInfo.db`` - Metadata about the offsets and lengths of compression chunks in the ``Data.db`` file. - -``Statistics.db`` - Stores metadata about the SSTable, including information about timestamps, tombstones, clustering keys, compaction, - repair, compression, TTLs, and more. - -``Digest.crc32`` - A CRC-32 digest of the ``Data.db`` file. - -``TOC.txt`` - A plain text list of the component files for the SSTable. - -Within the ``Data.db`` file, rows are organized by partition. These partitions are sorted in token order (i.e. by a -hash of the partition key when the default partitioner, ``Murmur3Partition``, is used). Within a partition, rows are -stored in the order of their clustering keys. - -SSTables can be optionally compressed using block-based compression. - -Guarantees ----------- - -.. todo:: todo diff --git a/doc/source/architecture/guarantees.rst b/doc/source/architecture/guarantees.rst new file mode 100644 index 0000000000..c0b58d880f --- /dev/null +++ b/doc/source/architecture/guarantees.rst @@ -0,0 +1,20 @@ +.. Licensed to the Apache Software Foundation (ASF) under one +.. or more contributor license agreements. See the NOTICE file +.. distributed with this work for additional information +.. regarding copyright ownership. The ASF licenses this file +.. to you under the Apache License, Version 2.0 (the +.. "License"); you may not use this file except in compliance +.. with the License. You may obtain a copy of the License at +.. +.. http://www.apache.org/licenses/LICENSE-2.0 +.. +.. Unless required by applicable law or agreed to in writing, software +.. distributed under the License is distributed on an "AS IS" BASIS, +.. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +.. See the License for the specific language governing permissions and +.. limitations under the License. + +Guarantees +---------- + +.. todo:: todo diff --git a/doc/source/architecture/index.rst b/doc/source/architecture/index.rst new file mode 100644 index 0000000000..58eda13779 --- /dev/null +++ b/doc/source/architecture/index.rst @@ -0,0 +1,29 @@ +.. Licensed to the Apache Software Foundation (ASF) under one +.. or more contributor license agreements. See the NOTICE file +.. distributed with this work for additional information +.. regarding copyright ownership. The ASF licenses this file +.. to you under the Apache License, Version 2.0 (the +.. "License"); you may not use this file except in compliance +.. with the License. You may obtain a copy of the License at +.. +.. http://www.apache.org/licenses/LICENSE-2.0 +.. +.. Unless required by applicable law or agreed to in writing, software +.. distributed under the License is distributed on an "AS IS" BASIS, +.. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +.. See the License for the specific language governing permissions and +.. limitations under the License. + +Architecture +============ + +This section describes the general architecture of Apache Cassandra. + +.. toctree:: + :maxdepth: 2 + + overview + dynamo + storage_engine + guarantees + diff --git a/doc/source/architecture/overview.rst b/doc/source/architecture/overview.rst new file mode 100644 index 0000000000..005b15b94c --- /dev/null +++ b/doc/source/architecture/overview.rst @@ -0,0 +1,20 @@ +.. Licensed to the Apache Software Foundation (ASF) under one +.. or more contributor license agreements. See the NOTICE file +.. distributed with this work for additional information +.. regarding copyright ownership. The ASF licenses this file +.. to you under the Apache License, Version 2.0 (the +.. "License"); you may not use this file except in compliance +.. with the License. You may obtain a copy of the License at +.. +.. http://www.apache.org/licenses/LICENSE-2.0 +.. +.. Unless required by applicable law or agreed to in writing, software +.. distributed under the License is distributed on an "AS IS" BASIS, +.. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +.. See the License for the specific language governing permissions and +.. limitations under the License. + +Overview +-------- + +.. todo:: todo diff --git a/doc/source/architecture/storage_engine.rst b/doc/source/architecture/storage_engine.rst new file mode 100644 index 0000000000..e4114e5afb --- /dev/null +++ b/doc/source/architecture/storage_engine.rst @@ -0,0 +1,82 @@ +.. Licensed to the Apache Software Foundation (ASF) under one +.. or more contributor license agreements. See the NOTICE file +.. distributed with this work for additional information +.. regarding copyright ownership. The ASF licenses this file +.. to you under the Apache License, Version 2.0 (the +.. "License"); you may not use this file except in compliance +.. with the License. You may obtain a copy of the License at +.. +.. http://www.apache.org/licenses/LICENSE-2.0 +.. +.. Unless required by applicable law or agreed to in writing, software +.. distributed under the License is distributed on an "AS IS" BASIS, +.. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +.. See the License for the specific language governing permissions and +.. limitations under the License. + +Storage Engine +-------------- + +.. _commit-log: + +CommitLog +^^^^^^^^^ + +.. todo:: todo + +.. _memtables: + +Memtables +^^^^^^^^^ + +Memtables are in-memory structures where Cassandra buffers writes. In general, there is one active memtable per table. +Eventually, memtables are flushed onto disk and become immutable `SSTables`_. This can be triggered in several +ways: + +- The memory usage of the memtables exceeds the configured threshold (see ``memtable_cleanup_threshold``) +- The :ref:`commit-log` approaches its maximum size, and forces memtable flushes in order to allow commitlog segments to + be freed + +Memtables may be stored entirely on-heap or partially off-heap, depending on ``memtable_allocation_type``. + +SSTables +^^^^^^^^ + +SSTables are the immutable data files that Cassandra uses for persisting data on disk. + +As SSTables are flushed to disk from :ref:`memtables` or are streamed from other nodes, Cassandra triggers compactions +which combine multiple SSTables into one. Once the new SSTable has been written, the old SSTables can be removed. + +Each SSTable is comprised of multiple components stored in separate files: + +``Data.db`` + The actual data, i.e. the contents of rows. + +``Index.db`` + An index from partition keys to positions in the ``Data.db`` file. For wide partitions, this may also include an + index to rows within a partition. + +``Summary.db`` + A sampling of (by default) every 128th entry in the ``Index.db`` file. + +``Filter.db`` + A Bloom Filter of the partition keys in the SSTable. + +``CompressionInfo.db`` + Metadata about the offsets and lengths of compression chunks in the ``Data.db`` file. + +``Statistics.db`` + Stores metadata about the SSTable, including information about timestamps, tombstones, clustering keys, compaction, + repair, compression, TTLs, and more. + +``Digest.crc32`` + A CRC-32 digest of the ``Data.db`` file. + +``TOC.txt`` + A plain text list of the component files for the SSTable. + +Within the ``Data.db`` file, rows are organized by partition. These partitions are sorted in token order (i.e. by a +hash of the partition key when the default partitioner, ``Murmur3Partition``, is used). Within a partition, rows are +stored in the order of their clustering keys. + +SSTables can be optionally compressed using block-based compression. diff --git a/doc/source/bugs.rst b/doc/source/bugs.rst new file mode 100644 index 0000000000..ef10aabf8b --- /dev/null +++ b/doc/source/bugs.rst @@ -0,0 +1,20 @@ +.. Licensed to the Apache Software Foundation (ASF) under one +.. or more contributor license agreements. See the NOTICE file +.. distributed with this work for additional information +.. regarding copyright ownership. The ASF licenses this file +.. to you under the Apache License, Version 2.0 (the +.. "License"); you may not use this file except in compliance +.. with the License. You may obtain a copy of the License at +.. +.. http://www.apache.org/licenses/LICENSE-2.0 +.. +.. Unless required by applicable law or agreed to in writing, software +.. distributed under the License is distributed on an "AS IS" BASIS, +.. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +.. See the License for the specific language governing permissions and +.. limitations under the License. + +Reporting bugs +-------------- + +.. todo:: TODO diff --git a/doc/source/conf.py b/doc/source/conf.py index 85c494d5fd..9caf188b76 100644 --- a/doc/source/conf.py +++ b/doc/source/conf.py @@ -192,7 +192,9 @@ html_static_path = ['_static'] # Additional templates that should be rendered to pages, maps page names to # template names. # -# html_additional_pages = {} +html_additional_pages = { + 'index': 'indexcontent.html' +} # If false, no module index is generated. # diff --git a/doc/source/configuration/cassandra_config_file.rst b/doc/source/configuration/cassandra_config_file.rst new file mode 100644 index 0000000000..b7d1bbc7fe --- /dev/null +++ b/doc/source/configuration/cassandra_config_file.rst @@ -0,0 +1,1699 @@ +Cassandra Configuration File +===================== + +``cluster_name`` +---------------- +The name of the cluster. This is mainly used to prevent machines in +one logical cluster from joining another. + +*Default Value:* 'Test Cluster' + +``num_tokens`` +-------------- + +This defines the number of tokens randomly assigned to this node on the ring +The more tokens, relative to other nodes, the larger the proportion of data +that this node will store. You probably want all nodes to have the same number +of tokens assuming they have equal hardware capability. + +If you leave this unspecified, Cassandra will use the default of 1 token for legacy compatibility, +and will use the initial_token as described below. + +Specifying initial_token will override this setting on the node's initial start, +on subsequent starts, this setting will apply even if initial token is set. + +If you already have a cluster with 1 token per node, and wish to migrate to +multiple tokens per node, see http://wiki.apache.org/cassandra/Operations + +*Default Value:* 256 + +``allocate_tokens_for_keyspace`` +-------------------------------- +*This option is commented out by default.* + +Triggers automatic allocation of num_tokens tokens for this node. The allocation +algorithm attempts to choose tokens in a way that optimizes replicated load over +the nodes in the datacenter for the replication strategy used by the specified +keyspace. + +The load assigned to each node will be close to proportional to its number of +vnodes. + +Only supported with the Murmur3Partitioner. + +*Default Value:* KEYSPACE + +``initial_token`` +----------------- +*This option is commented out by default.* + +initial_token allows you to specify tokens manually. While you can use it with +vnodes (num_tokens > 1, above) -- in which case you should provide a +comma-separated list -- it's primarily used when adding nodes to legacy clusters +that do not have vnodes enabled. + +``hinted_handoff_enabled`` +-------------------------- + +See http://wiki.apache.org/cassandra/HintedHandoff +May either be "true" or "false" to enable globally + +*Default Value:* true + +``hinted_handoff_disabled_datacenters`` +--------------------------------------- +*This option is commented out by default.* + +When hinted_handoff_enabled is true, a black list of data centers that will not +perform hinted handoff + +*Default Value (complex option)*:: + + # - DC1 + # - DC2 + +``max_hint_window_in_ms`` +------------------------- +this defines the maximum amount of time a dead host will have hints +generated. After it has been dead this long, new hints for it will not be +created until it has been seen alive and gone down again. + +*Default Value:* 10800000 # 3 hours + +``hinted_handoff_throttle_in_kb`` +--------------------------------- + +Maximum throttle in KBs per second, per delivery thread. This will be +reduced proportionally to the number of nodes in the cluster. (If there +are two nodes in the cluster, each delivery thread will use the maximum +rate; if there are three, each will throttle to half of the maximum, +since we expect two nodes to be delivering hints simultaneously.) + +*Default Value:* 1024 + +``max_hints_delivery_threads`` +------------------------------ + +Number of threads with which to deliver hints; +Consider increasing this number when you have multi-dc deployments, since +cross-dc handoff tends to be slower + +*Default Value:* 2 + +``hints_directory`` +------------------- +*This option is commented out by default.* + +Directory where Cassandra should store hints. +If not set, the default directory is $CASSANDRA_HOME/data/hints. + +*Default Value:* /var/lib/cassandra/hints + +``hints_flush_period_in_ms`` +---------------------------- + +How often hints should be flushed from the internal buffers to disk. +Will *not* trigger fsync. + +*Default Value:* 10000 + +``max_hints_file_size_in_mb`` +----------------------------- + +Maximum size for a single hints file, in megabytes. + +*Default Value:* 128 + +``hints_compression`` +--------------------- +*This option is commented out by default.* + +Compression to apply to the hint files. If omitted, hints files +will be written uncompressed. LZ4, Snappy, and Deflate compressors +are supported. + +*Default Value (complex option)*:: + + # - class_name: LZ4Compressor + # parameters: + # - + +``batchlog_replay_throttle_in_kb`` +---------------------------------- +Maximum throttle in KBs per second, total. This will be +reduced proportionally to the number of nodes in the cluster. + +*Default Value:* 1024 + +``authenticator`` +----------------- + +Authentication backend, implementing IAuthenticator; used to identify users +Out of the box, Cassandra provides org.apache.cassandra.auth.{AllowAllAuthenticator, +PasswordAuthenticator}. + +- AllowAllAuthenticator performs no checks - set it to disable authentication. +- PasswordAuthenticator relies on username/password pairs to authenticate + users. It keeps usernames and hashed passwords in system_auth.credentials table. + Please increase system_auth keyspace replication factor if you use this authenticator. + If using PasswordAuthenticator, CassandraRoleManager must also be used (see below) + +*Default Value:* AllowAllAuthenticator + +``authorizer`` +-------------- + +Authorization backend, implementing IAuthorizer; used to limit access/provide permissions +Out of the box, Cassandra provides org.apache.cassandra.auth.{AllowAllAuthorizer, +CassandraAuthorizer}. + +- AllowAllAuthorizer allows any action to any user - set it to disable authorization. +- CassandraAuthorizer stores permissions in system_auth.permissions table. Please + increase system_auth keyspace replication factor if you use this authorizer. + +*Default Value:* AllowAllAuthorizer + +``role_manager`` +---------------- + +Part of the Authentication & Authorization backend, implementing IRoleManager; used +to maintain grants and memberships between roles. +Out of the box, Cassandra provides org.apache.cassandra.auth.CassandraRoleManager, +which stores role information in the system_auth keyspace. Most functions of the +IRoleManager require an authenticated login, so unless the configured IAuthenticator +actually implements authentication, most of this functionality will be unavailable. + +- CassandraRoleManager stores role data in the system_auth keyspace. Please + increase system_auth keyspace replication factor if you use this role manager. + +*Default Value:* CassandraRoleManager + +``roles_validity_in_ms`` +------------------------ + +Validity period for roles cache (fetching granted roles can be an expensive +operation depending on the role manager, CassandraRoleManager is one example) +Granted roles are cached for authenticated sessions in AuthenticatedUser and +after the period specified here, become eligible for (async) reload. +Defaults to 2000, set to 0 to disable caching entirely. +Will be disabled automatically for AllowAllAuthenticator. + +*Default Value:* 2000 + +``roles_update_interval_in_ms`` +------------------------------- +*This option is commented out by default.* + +Refresh interval for roles cache (if enabled). +After this interval, cache entries become eligible for refresh. Upon next +access, an async reload is scheduled and the old value returned until it +completes. If roles_validity_in_ms is non-zero, then this must be +also. +Defaults to the same value as roles_validity_in_ms. + +*Default Value:* 2000 + +``permissions_validity_in_ms`` +------------------------------ + +Validity period for permissions cache (fetching permissions can be an +expensive operation depending on the authorizer, CassandraAuthorizer is +one example). Defaults to 2000, set to 0 to disable. +Will be disabled automatically for AllowAllAuthorizer. + +*Default Value:* 2000 + +``permissions_update_interval_in_ms`` +------------------------------------- +*This option is commented out by default.* + +Refresh interval for permissions cache (if enabled). +After this interval, cache entries become eligible for refresh. Upon next +access, an async reload is scheduled and the old value returned until it +completes. If permissions_validity_in_ms is non-zero, then this must be +also. +Defaults to the same value as permissions_validity_in_ms. + +*Default Value:* 2000 + +``credentials_validity_in_ms`` +------------------------------ + +Validity period for credentials cache. This cache is tightly coupled to +the provided PasswordAuthenticator implementation of IAuthenticator. If +another IAuthenticator implementation is configured, this cache will not +be automatically used and so the following settings will have no effect. +Please note, credentials are cached in their encrypted form, so while +activating this cache may reduce the number of queries made to the +underlying table, it may not bring a significant reduction in the +latency of individual authentication attempts. +Defaults to 2000, set to 0 to disable credentials caching. + +*Default Value:* 2000 + +``credentials_update_interval_in_ms`` +------------------------------------- +*This option is commented out by default.* + +Refresh interval for credentials cache (if enabled). +After this interval, cache entries become eligible for refresh. Upon next +access, an async reload is scheduled and the old value returned until it +completes. If credentials_validity_in_ms is non-zero, then this must be +also. +Defaults to the same value as credentials_validity_in_ms. + +*Default Value:* 2000 + +``partitioner`` +--------------- + +The partitioner is responsible for distributing groups of rows (by +partition key) across nodes in the cluster. You should leave this +alone for new clusters. The partitioner can NOT be changed without +reloading all data, so when upgrading you should set this to the +same partitioner you were already using. + +Besides Murmur3Partitioner, partitioners included for backwards +compatibility include RandomPartitioner, ByteOrderedPartitioner, and +OrderPreservingPartitioner. + + +*Default Value:* org.apache.cassandra.dht.Murmur3Partitioner + +``data_file_directories`` +------------------------- +*This option is commented out by default.* + +Directories where Cassandra should store data on disk. Cassandra +will spread data evenly across them, subject to the granularity of +the configured compaction strategy. +If not set, the default directory is $CASSANDRA_HOME/data/data. + +*Default Value (complex option)*:: + + # - /var/lib/cassandra/data + +``commitlog_directory`` +----------------------- +*This option is commented out by default.* +commit log. when running on magnetic HDD, this should be a +separate spindle than the data directories. +If not set, the default directory is $CASSANDRA_HOME/data/commitlog. + +*Default Value:* /var/lib/cassandra/commitlog + +``disk_failure_policy`` +----------------------- + +Policy for data disk failures: + +die + shut down gossip and client transports and kill the JVM for any fs errors or + single-sstable errors, so the node can be replaced. + +stop_paranoid + shut down gossip and client transports even for single-sstable errors, + kill the JVM for errors during startup. + +stop + shut down gossip and client transports, leaving the node effectively dead, but + can still be inspected via JMX, kill the JVM for errors during startup. + +best_effort + stop using the failed disk and respond to requests based on + remaining available sstables. This means you WILL see obsolete + data at CL.ONE! + +ignore + ignore fatal errors and let requests fail, as in pre-1.2 Cassandra + +*Default Value:* stop + +``commit_failure_policy`` +------------------------- + +Policy for commit disk failures: + +die + shut down gossip and Thrift and kill the JVM, so the node can be replaced. + +stop + shut down gossip and Thrift, leaving the node effectively dead, but + can still be inspected via JMX. + +stop_commit + shutdown the commit log, letting writes collect but + continuing to service reads, as in pre-2.0.5 Cassandra + +ignore + ignore fatal errors and let the batches fail + +*Default Value:* stop + +``prepared_statements_cache_size_mb`` +------------------------------------- + +Maximum size of the native protocol prepared statement cache + +Valid values are either "auto" (omitting the value) or a value greater 0. + +Note that specifying a too large value will result in long running GCs and possbily +out-of-memory errors. Keep the value at a small fraction of the heap. + +If you constantly see "prepared statements discarded in the last minute because +cache limit reached" messages, the first step is to investigate the root cause +of these messages and check whether prepared statements are used correctly - +i.e. use bind markers for variable parts. + +Do only change the default value, if you really have more prepared statements than +fit in the cache. In most cases it is not neccessary to change this value. +Constantly re-preparing statements is a performance penalty. + +Default value ("auto") is 1/256th of the heap or 10MB, whichever is greater + +``thrift_prepared_statements_cache_size_mb`` +-------------------------------------------- + +Maximum size of the Thrift prepared statement cache + +If you do not use Thrift at all, it is safe to leave this value at "auto". + +See description of 'prepared_statements_cache_size_mb' above for more information. + +Default value ("auto") is 1/256th of the heap or 10MB, whichever is greater + +``key_cache_size_in_mb`` +------------------------ + +Maximum size of the key cache in memory. + +Each key cache hit saves 1 seek and each row cache hit saves 2 seeks at the +minimum, sometimes more. The key cache is fairly tiny for the amount of +time it saves, so it's worthwhile to use it at large numbers. +The row cache saves even more time, but must contain the entire row, +so it is extremely space-intensive. It's best to only use the +row cache if you have hot rows or static rows. + +NOTE: if you reduce the size, you may not get you hottest keys loaded on startup. + +Default value is empty to make it "auto" (min(5% of Heap (in MB), 100MB)). Set to 0 to disable key cache. + +``key_cache_save_period`` +------------------------- + +Duration in seconds after which Cassandra should +save the key cache. Caches are saved to saved_caches_directory as +specified in this configuration file. + +Saved caches greatly improve cold-start speeds, and is relatively cheap in +terms of I/O for the key cache. Row cache saving is much more expensive and +has limited use. + +Default is 14400 or 4 hours. + +*Default Value:* 14400 + +``key_cache_keys_to_save`` +-------------------------- +*This option is commented out by default.* + +Number of keys from the key cache to save +Disabled by default, meaning all keys are going to be saved + +*Default Value:* 100 + +``row_cache_class_name`` +------------------------ +*This option is commented out by default.* + +Row cache implementation class name. Available implementations: + +org.apache.cassandra.cache.OHCProvider + Fully off-heap row cache implementation (default). + +org.apache.cassandra.cache.SerializingCacheProvider + This is the row cache implementation availabile + in previous releases of Cassandra. + +*Default Value:* org.apache.cassandra.cache.OHCProvider + +``row_cache_size_in_mb`` +------------------------ + +Maximum size of the row cache in memory. +Please note that OHC cache implementation requires some additional off-heap memory to manage +the map structures and some in-flight memory during operations before/after cache entries can be +accounted against the cache capacity. This overhead is usually small compared to the whole capacity. +Do not specify more memory that the system can afford in the worst usual situation and leave some +headroom for OS block level cache. Do never allow your system to swap. + +Default value is 0, to disable row caching. + +*Default Value:* 0 + +``row_cache_save_period`` +------------------------- + +Duration in seconds after which Cassandra should save the row cache. +Caches are saved to saved_caches_directory as specified in this configuration file. + +Saved caches greatly improve cold-start speeds, and is relatively cheap in +terms of I/O for the key cache. Row cache saving is much more expensive and +has limited use. + +Default is 0 to disable saving the row cache. + +*Default Value:* 0 + +``row_cache_keys_to_save`` +-------------------------- +*This option is commented out by default.* + +Number of keys from the row cache to save. +Specify 0 (which is the default), meaning all keys are going to be saved + +*Default Value:* 100 + +``counter_cache_size_in_mb`` +---------------------------- + +Maximum size of the counter cache in memory. + +Counter cache helps to reduce counter locks' contention for hot counter cells. +In case of RF = 1 a counter cache hit will cause Cassandra to skip the read before +write entirely. With RF > 1 a counter cache hit will still help to reduce the duration +of the lock hold, helping with hot counter cell updates, but will not allow skipping +the read entirely. Only the local (clock, count) tuple of a counter cell is kept +in memory, not the whole counter, so it's relatively cheap. + +NOTE: if you reduce the size, you may not get you hottest keys loaded on startup. + +Default value is empty to make it "auto" (min(2.5% of Heap (in MB), 50MB)). Set to 0 to disable counter cache. +NOTE: if you perform counter deletes and rely on low gcgs, you should disable the counter cache. + +``counter_cache_save_period`` +----------------------------- + +Duration in seconds after which Cassandra should +save the counter cache (keys only). Caches are saved to saved_caches_directory as +specified in this configuration file. + +Default is 7200 or 2 hours. + +*Default Value:* 7200 + +``counter_cache_keys_to_save`` +------------------------------ +*This option is commented out by default.* + +Number of keys from the counter cache to save +Disabled by default, meaning all keys are going to be saved + +*Default Value:* 100 + +``saved_caches_directory`` +-------------------------- +*This option is commented out by default.* + +saved caches +If not set, the default directory is $CASSANDRA_HOME/data/saved_caches. + +*Default Value:* /var/lib/cassandra/saved_caches + +``commitlog_sync`` +------------------ +*This option is commented out by default.* + +commitlog_sync may be either "periodic" or "batch." + +When in batch mode, Cassandra won't ack writes until the commit log +has been fsynced to disk. It will wait +commitlog_sync_batch_window_in_ms milliseconds between fsyncs. +This window should be kept short because the writer threads will +be unable to do extra work while waiting. (You may need to increase +concurrent_writes for the same reason.) + + +*Default Value:* batch + +``commitlog_sync_batch_window_in_ms`` +------------------------------------- +*This option is commented out by default.* + +*Default Value:* 2 + +``commitlog_sync`` +------------------ + +the other option is "periodic" where writes may be acked immediately +and the CommitLog is simply synced every commitlog_sync_period_in_ms +milliseconds. + +*Default Value:* periodic + +``commitlog_sync_period_in_ms`` +------------------------------- + +*Default Value:* 10000 + +``commitlog_segment_size_in_mb`` +-------------------------------- + +The size of the individual commitlog file segments. A commitlog +segment may be archived, deleted, or recycled once all the data +in it (potentially from each columnfamily in the system) has been +flushed to sstables. + +The default size is 32, which is almost always fine, but if you are +archiving commitlog segments (see commitlog_archiving.properties), +then you probably want a finer granularity of archiving; 8 or 16 MB +is reasonable. +Max mutation size is also configurable via max_mutation_size_in_kb setting in +cassandra.yaml. The default is half the size commitlog_segment_size_in_mb * 1024. + +NOTE: If max_mutation_size_in_kb is set explicitly then commitlog_segment_size_in_mb must +be set to at least twice the size of max_mutation_size_in_kb / 1024 + + +*Default Value:* 32 + +``commitlog_compression`` +------------------------- +*This option is commented out by default.* + +Compression to apply to the commit log. If omitted, the commit log +will be written uncompressed. LZ4, Snappy, and Deflate compressors +are supported. + +*Default Value (complex option)*:: + + # - class_name: LZ4Compressor + # parameters: + # - + +``seed_provider`` +----------------- +any class that implements the SeedProvider interface and has a +constructor that takes a Map