Compactor: Context deadline exceeded in filter blocks

[ben-ganley]

Thanos version used: 0.39.2, bitnami/thanos:0.39.2-debian-12-r0

Object Storage Provider: S3

What happened: Context deadline is exceeded, blocks never seem to be deleted from storage and continue to accumulate

What you expected to happen: The blocks should be able to be filtered successfully and deleted from storage after retention expires.

Full logs to relevant components:

ts=2025-08-20T22:08:57.030820405Z caller=compact.go:636 level=error msg="retriable error" err="syncing metas: filter metas: filter blocks marked for no downsample: context deadline exceeded"
ts=2025-08-20T22:08:57.031275592Z caller=compact.go:665 level=error msg="retriable error" err="filter metas: filter blocks marked for no downsample: context deadline exceeded"

Anything else we need to know:

There are about 80k objects in the bucket.

We have looked over available settings for the compactor and have tried adjusting some but unsure as to the real source / cause of this error and which settings or configuration may resolve it.

[GiedriusS]

Try bumping --block-meta-fetch-concurrency.