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## 23.5. Kernel configuration

These are the configuration options you can pass to the neo4j kernel. They can either be passed as a map when using the embedded database, or in the neo4j.properties file when using the Neo4j Server.

All stores total mapped memory size

Default value: `524288000`
`all_stores_total_mapped_memory_size` The size to allocate for a memory mapping pool to be shared between all stores.

Allow store upgrade

Default value: `false`
`allow_store_upgrade` Whether to allow a store upgrade in case the current version of the database starts against an older store version. Setting this to true does not guarantee successful upgrade, just that it allows an attempt at it.

Array block size

Default value: `120`
`array_block_size` Specifies the block size for storing arrays. This parameter is only honored when the store is created, otherwise it is ignored. The default block size is 120 bytes, and the overhead of each block is the same as for string blocks, i.e., 8 bytes.

Backup slave

Default value: `false`
`backup_slave` Mark this database as a backup slave.

Cache type

Default value: `soft`
`cache_type` The type of cache to use for nodes and relationships. Note that the Neo4j Enterprise Edition has the additional 'hpc' cache type (High-Performance Cache). See the chapter on caches in the manual for more information.

Cypher parser version

`cypher_parser_version` Enable this to specify a parser other than the default one.

Dense node threshold

Default value: `50`
`dense_node_threshold` Relationship count threshold for considering a node dense

Dump configuration

Default value: `false`
`dump_configuration` Print out the effective Neo4j configuration after startup.

Forced kernel id

`forced_kernel_id` An identifier that uniquely identifies this graph database instance within this JVM. Defaults to an auto-generated number depending on how many instance are started in this JVM.

Gc monitor threshold

Default value: `200`
`gc_monitor_threshold` The amount of time in ms the monitor thread has to be blocked before logging a message it was blocked.

Gc monitor wait time

Default value: `100`
`gc_monitor_wait_time` Amount of time in ms the GC monitor thread will wait before taking another measurement.

Intercept committing transactions

Default value: `false`
`intercept_committing_transactions` Determines whether any TransactionInterceptors loaded will intercept prepared transactions before they reach the logical log.

Intercept deserialized transactions

Default value: `false`
`intercept_deserialized_transactions` Determines whether any TransactionInterceptors loaded will intercept externally received transactions (e.g. in HA) before they reach the logical log and are applied to the store.

Keep logical logs

Default value: `true`
`keep_logical_logs` Make Neo4j keep the logical transaction logs for being able to backup the database.Can be used for specifying the threshold to prune logical logs after. For example "10 days" will prune logical logs that only contains transactions older than 10 days from the current time, or "100k txs" will keep the 100k latest transactions and prune any older transactions.

Label block size

Default value: `60`
`label_block_size` Specifies the block size for storing labels exceeding in-lined space in node record. This parameter is only honored when the store is created, otherwise it is ignored. The default block size is 60 bytes, and the overhead of each block is the same as for string blocks, i.e., 8 bytes.

Log mapped memory stats

Default value: `false`
`log_mapped_memory_stats` Tell Neo4j to regularly log memory mapping statistics.

Log mapped memory stats filename

Default value: `mapped_memory_stats.log`
`log_mapped_memory_stats_filename` The file where Neo4j will record memory mapping statistics.

Log mapped memory stats interval

Default value: `1000000`
`log_mapped_memory_stats_interval` The number of records to be loaded between regular logging of memory mapping statistics.

Logging.threshold for rotation

Default value: `104857600`
`logging.threshold_for_rotation` Threshold in bytes for when database logs (text logs, for debugging, that is) are rotated.

Logical log

Default value: `nioneo_logical.log`
`logical_log` The base name for the logical log files, either an absolute path or relative to the store_dir setting. This should generally not be changed.

Logical log rotation threshold

Default value: `26214400`
`logical_log_rotation_threshold` Specifies at which file size the logical log will auto-rotate. 0 means that no rotation will automatically occur based on file size. Default is 25M

Lucene searcher cache size

Default value: `2147483647`
`lucene_searcher_cache_size` Integer value that sets the maximum number of open lucene index searchers.

Mapped memory page size

Default value: `1048576`
`mapped_memory_page_size` Target size for pages of mapped memory.

Neo store

Default value: `neostore`
`neo_store` The base name for the Neo4j Store files, either an absolute path or relative to the store_dir setting. This should generally not be changed.

Neostore.nodestore.db.mapped memory

Default value: `20971520`
`neostore.nodestore.db.mapped_memory` The size to allocate for memory mapping the node store.

Neostore.propertystore.db.arrays.mapped memory

Default value: `136314880`
`neostore.propertystore.db.arrays.mapped_memory` The size to allocate for memory mapping the array property store.

Neostore.propertystore.db.index.keys.mapped memory

Default value: `1048576`
`neostore.propertystore.db.index.keys.mapped_memory` The size to allocate for memory mapping the store for property key strings.

Neostore.propertystore.db.index.mapped memory

Default value: `1048576`
`neostore.propertystore.db.index.mapped_memory` The size to allocate for memory mapping the store for property key indexes.

Neostore.propertystore.db.mapped memory

Default value: `94371840`
`neostore.propertystore.db.mapped_memory` The size to allocate for memory mapping the property value store.

Neostore.propertystore.db.strings.mapped memory

Default value: `136314880`
`neostore.propertystore.db.strings.mapped_memory` The size to allocate for memory mapping the string property store.

Neostore.relationshipstore.db.mapped memory

Default value: `104857600`
`neostore.relationshipstore.db.mapped_memory` The size to allocate for memory mapping the relationship store.

Node auto indexing

Default value: `false`
`node_auto_indexing` Controls the auto indexing feature for nodes. Setting to false shuts it down, while true enables it by default for properties listed in the node_keys_indexable setting.

Node keys indexable

`node_keys_indexable` A list of property names (comma separated) that will be indexed by default. This applies to Nodes only.

Query cache size

Default value: `100`
`query_cache_size` Used to set the number of Cypher query execution plans that are cached.

Read only database

Default value: `false`
`read_only` Only allow read operations from this Neo4j instance. This mode still requires write access to the directory for lock purposes

Rebuild idgenerators fast

Default value: `true`
`rebuild_idgenerators_fast` Use a quick approach for rebuilding the ID generators. This give quicker recovery time, but will limit the ability to reuse the space of deleted entities.

Relationship auto indexing

Default value: `false`
`relationship_auto_indexing` Controls the auto indexing feature for relationships. Setting to false shuts it down, while true enables it by default for properties listed in the relationship_keys_indexable setting.

Relationship grab size

Default value: `100`
`relationship_grab_size` How many relationships to read at a time during iteration

Relationship keys indexable

`relationship_keys_indexable` A list of property names (comma separated) that will be indexed by default. This applies to Relationships only.

Remote logging enabled

Default value: `false`
`remote_logging_enabled` Whether to enable logging to a remote server or not.

Remote logging host

Default value: `127.0.0.1`
`remote_logging_host` Host for remote logging using LogBack SocketAppender.

Remote logging port

Default value: `4560`
`remote_logging_port` Port for remote logging using LogBack SocketAppender.

Store dir

`store_dir` The directory where the database files are located.

String block size

Default value: `120`
`string_block_size` Specifies the block size for storing strings. This parameter is only honored when the store is created, otherwise it is ignored. Note that each character in a string occupies two bytes, meaning that a block size of 120 (the default size) will hold a 60 character long string before overflowing into a second block. Also note that each block carries an overhead of 8 bytes. This means that if the block size is 120, the size of the stored records will be 128 bytes.

Tx manager impl

Default value: `native`
`tx_manager_impl` The name of the Transaction Manager service to use as defined in the TM service provider constructor.

Use memory mapped buffers

Default value: `true`
`use_memory_mapped_buffers` Tell Neo4j to use memory mapped buffers for accessing the native storage layer.

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