Potential high latency when destroying an iterator

[sryanyuan]

PurgeObsoleteFiles will be called during compaction, flush, and similar operations, and it will be performed in the background threads (avoid-unnecessary-blocking-io is enabled).

Additionally, it may also be triggered when destroying an iterator in a user thread, in the case:

• SST files will be deleted by background threads
• while archived WAL log files will be unlinked directly in the user thread.

This design might cause high latency if there are many files to be deleted.

Question:

Are there any solutions to mitigate this latency issue if iterator operations are frequently performed?