Understanding logical logs and effects of parameters keep_logical_logs and logical_log_rotation_threshold

Neo4j maintains logical logs for incremental backup and cluster consistency. The logical logs are named as follows:

pre 2.2

data/graph.db/nioneo_logical.log*

2.2 forward

data/graph.db/neostore.transaction.db*

When one runs a database backup, via bin/neo4j-backup, if the -to <target directory> has a previous backup, then the backup will be an incremental backup rather than a full backup. If the logical logs have been rotated out since the last full backup, then the backup is forced to be a full backup.   

In a cluster environment the logical logs are utilized to ensure that a newly discovered slave is updated with the correct transactions. If the logical logs have been rotated out, then rather than simply updating the new slave from the logical logs, a complete store copy will occur.

Within the conf/neo4j.properties, one can configure the following two parameters:

logical_log_rotation_threshold
keep_logical_logs

Each of these parameters are documented in the Neo4j documentation. In summary the logical_log_rotation_threshold determines to what size the current logical log file can grow before it is rotated out. For example the default under 2.3.0 for logical_log_rotation_threshold is 250M. As such, one will expect no files under data/graph.db/neostore.transaction.db to exceed 250M. At the point that the neostore.transaction.db.<N> reaches 250M the neostore.transaction.db.<N> will be rotated to neostore.transaction.db.<N+1> and then the keep_logical_logs parameter will be consulted to determine if prior neostore.transaction.db.<N> files should be automatically removed. 

For example if

logical_log_rotation_threshold=250M
keep_logical_logs=3 days

then when the neostore.transaction.db.<N> exceeds 250M we will create a neostore.transaction.db.<N+1> and then auto remove any neostore.transaction.db.<N> which are older than 3 days. The important part to remember is that the removal of files per the parameter for keep_logical_logs is only considered when the logical_log_rotation_threshold has been met.   

Additionally, if initially

logical_log_rotation_threshold=250M
keep_logical_logs=10 days

and then one edits conf/neo4j.properties and changes

keep_logical_logs=10 days

to

keep_logical_logs=5 days

and then restarts Neo4j, there will still be neostore.transaction.db.<N> for the last 10 days. When the current neostore.transaction.db reaches 250M then we will remove logical logs from all but the last five days. ”’

  • Last Modified: 2020-09-23 21:26:58 UTC by Dana Canzano.
  • Relevant for Neo4j Versions: 2.0.
  • Relevant keywords server,configuration.