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:
| Setting | Description |
|---|---|
| index.translog.flush_threshold_ops | After how many operations to flush. Defaults to 5000. |
| index.translog.flush_threshold_size | Once the translog hits this size, a flush will happen. Defaults to 500mb. |
| index.translog.flush_threshold_period | The period with no flush happening to force a flush. Defaults to 60m. |