Is this Async index?
Async indexing jobs are by default configured to run at an interval of 5 seconds which can be configured via the OSGi config -> org.apache.jackrabbit.oak.plugins.index.AsyncIndexerService.
If you are changing the index definition, then you need to manually reindex it otherwise incremental indexing is performed based on the type of index:
async -> Every 5 Seconds
fulltext-aync -> Every 5 seconds
nrt -> Real-time index update with no delays
Also, Changing the "Async Indexer Configs" at "OSGi config -> org.apache.jackrabbit.oak.plugins.index.AsyncIndexerService" will have a performance impact if you change it to less than 5 and you might not get expected results if you change it to more than 5 as almost every AEM console uses aync,fulltext-aync index types.
This config should only be changed if recommended by Adobe Engineer after analyzing the complete use case.
Yes I updated my custom index to async. I dont know we have osgi config-> org.apache.jackrabbit.oak.plugins.index.AsyncIndexerService
Is there away to validate the that AsyncIndexerService completed re-indexing for my custom index. in logs ?
Yes, I provided the config to let you know how the indexer service is configured by default.
To check the Async index stats, you can leverage IndexStats mbean http://localhost:4502/system/console/jmx/org.apache.jackrabbit.oak%3Aname%3Dasync%2Ctype%3DIndexStat...
But this will not provide informaiton specifically about your custom index.
Debug level logs for the appender: org.apache.jackrabbit.oak.plugins.index.AsyncIndexUpdate and org.apache.jackrabbit.oak.plugins.index.IndexUpdate might be helpful to know whats happening with reindexing. This would really fill up logs though.