Current behavior

The rebuild local index step will be performed if index is up to 10% behind the DB. The threshold value can't be modified.

Expected behavior

The percentage threshold is configurable by an administrator.

Notes

Since 9.1 the index startup flow consists of 3 steps:

1. Re-index missing data if a local issue index is less than 10% behind the database. Since 9.3 the percentage is configurable.
2. Load a recent index snapshot from shared-home directory if one is available.
3. Otherwise trigger a full re-index.

(From https://confluence.atlassian.com/jirakb/index-management-on-jira-start-up-1141500654.html)

Step 1 percentage tolerance is set to 10% and can't be modified. The time to re-index 10% is depends on the number of issues this value represents. For bigger instances this means longer times of the catch up. For them it might be more beneficial to go to step 2 (fetching index from shared and restoring it) even if less than 10% of issues need to be re-indexed.