Online disk store compaction doesn't seem to work

Products

• VMware Tanzu Gemfire

Issue/Introduction

Symptoms:

The javadocs for online disk store compaction-threshold imply that GemFire compact as soon as the amount of garbage is equal or greater than the threshold.

From DiskStoreFactory.setCompactionThreshold:

When the amount of garbage in an oplog exceeds this percentage then when a compaction
 * is done this garbage will be cleaned up freeing up disk space. Garbage is created by
 * entry destroys, entry updates, and region destroys.

However GemFire actually trigger compaction when the amount of non-garbage data is equal or less than the threshold instead so online disk store compaction appears not to be working.

Environment

Resolution

If you set a threshold of 20% then GemFire doesn't trigger compaction until the *live* data is less than 20%. If you need a threshold of 20% you should be setting the threshold to 80% instead. This issue is fixed in version 9.0 of GemFire.