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Each shard has a transaction log or write ahead log associated with it. It allows to guarantee that when an index/delete operation occurs, it is applied atomically, while not "committing" the internal Lucene index for each request. A flush ("commit") still happens based on several parameters:
After how many operations to flush. Defaults to
Once the translog hits this size, a flush will happen. Defaults to
The period with no flush happening to force a flush. Defaults to
How often to check if a flush is needed, randomized
between the interval value and 2x the interval value. Defaults to
How often the translog is
fsynced to disk. Defaults to
Note: these parameters except
index.gateway.local.sync can be updated at runtime using the Index
Settings Update API (for example, these numbers can be increased when
executing bulk updates to support higher TPS)