Index Modules are modules created per index and control all aspects related to an index. Since those modules lifecycle are tied to an index, all the relevant modules settings can be provided when creating an index (and it is actually the recommended way to configure an index).
There are specific index level settings that are not associated with any specific module. These include:
Should the compound file format be used (boolean setting). The compound format was created to reduce the number of open file handles when using file based storage. However, by default it is set to
falseas the non-compound format gives better performance. It is important that OS is configured to give Elasticsearch “enough” file handles. See the section called “File Descriptors”.
compound_formatcan be set to a number between
trueand a number inbetween represents a percentage: if the merged segment is less than this percentage of the total index, then it is written in compound format, otherwise it is written in non-compound format.
Should a new segment (create by indexing, not by merging) be written
in compound format or non-compound format? Defaults to
true. This is a dynamic setting.
A time setting controlling how often the
refresh operation will be executed. Defaults to
1s. Can be set to
-1in order to disable it.
Should shard consistency be checked upon opening.
true, the shard will be checked, preventing it from being open in case some segments appear to be corrupted. When
fix, the shard will also be checked but segments that were reported as corrupted will be automatically removed. Default value is
false, which doesn’t check shards.
Checking shards may take a lot of time on large indices.
fix may result in data loss,
use with caution.