Significant tsidx performance improvements are turned off by default
Splunk Enterprise 7.2 introduces a change to the file format of tsidx index files, resulting in significant size reduction. The reduced file size leads to improved search performance through decreased I/O, improved utilization of SmartSearch caches, and so on.
This change is beneficial under all circumstances. However, to upgrade multisite indexer clusters without search interruption, it is necessary to defer the format change until after the upgrade completes and all peer nodes can switch to the new format simultaneously. For this reason, Splunk Enterprise 7.2 ships with the feature turned off by default.
Turn this feature on, immediately after you complete your 7.2 upgrade.
To turn on the feature, edit indexes.conf on each indexer (or, in the case of indexer clusters, in the master node's configuration bundle). Set tsidxWritingLevel to 2. Make this change in the default section of the file, so that it applies to all indexes: