Performance slowdown due to preenlarge mechanism when disk usage is high
Details
| Detail name | Value |
|---|---|
| Changelog Number | 24360 |
| Type | Bug |
| Status | Resolved |
| Affected Versions | Exasol 8.0.0 |
| Fix Versions | Exasol 8.34.0, Exasol 8.29.10 |
| Resolution Date | 2025-04-16 |
Description
Database performs a preenlarge operation on the persistent device to always have free space for upcoming write operations for minor performance reasons. If database cannot enlarge the volume due to disk space issues, this preenlarge operation will fail. The enlargement operation is repeated too often, which can slow down the performance of the database. The performance impact increases with the number of nodes and the size of the data stored in the persistent volume.
Workaround
Disable the preenlarge mechanism. This can be done by adding the DB parameter "-preEnlargementUsageThreshold=0" (see Add Database Parameters). Please consult with Exasol Support to confirm that your database is affected. In such a Support case customer needs to provide evidence from Statistical System Tables that system performance is consistently degraded.
Fix
The preenlarge operation is triggered much less frequently and has improved performance. There is no longer any negative performance impact from the preenlarge mechanism.
