Additional to that if you see the below ERROR as well you can also increase the value of maxConcurrentOptimizes in indexes.conf for a particular index which is affected or you can set globally to all the indexes depends on your requirement.
ERROR:
04-11-2019 11:01:51.574 +0500 ERROR SplunkOptimize - (child_39286__SplunkOptimize) optimize finished: failed, see rc for more details, dir=C:\Program Files\Splunk\var\lib\splunk_internaldb\db\hot_v1_268, rc=-12 (unsigned 244), errno=0
04-11-2019 11:01:51.574 +0500 ERROR SplunkOptimize - (child_39286__SplunkOptimize) merge failed for path=C:\Program Files\Splunk\var\lib\splunk_internaldb\db\hot_v1_268 rc=-12 wrc=-12 errno=0 file=dontknow hint=tsval_id is UINT_MAX in _merge_all_postings]
Example:
In indexes.conf
For particular index:
[_internal]
maxConcurrentOptimizes = < desired value >
For all the indexes:
[default]
maxConcurrentOptimizes = < desigered value >
maxConcurrentOptimizes = < nonnegative integer >
The number of concurrent optimize processes that can run against the hot
DB.
This number should be increased if:
There are always many small tsidx files in the hot DB.
After rolling, there are many tsidx files in warm or cold DB.
Must restart splunkd after changing this parameter; index reload will not
suffice.
Highest legal value is 4294967295
Defaults to 6
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