[Store] Metric to capture timestamp of the last loaded block

[spaparaju]

Signed-off-by: SriKrishna Paparaju paparaju@gmail.com

Currently Thanos does not have visibility into when a block is loaded . Lack of this visibility can be a challenge either with chosen downsampling options (or any other reason) might cause data loss and there is no way to know the extent of the data loss. This PR adds metric to capture timestamp of the last loaded block.

• I added CHANGELOG entry for this change.
• Change is not relevant to the end user.

Changes

Verification

Added unit test logic, tested thru 'TestBucketStore_e2e() of github.com/thanos-io/thanos/pkg/store'

[matej-g]

I think it looks fine 👍 But maybe could you give us a bit more context why this is required? What is the use case for it etc.?

[spaparaju]

I think it looks fine 👍 But maybe could you give us a bit more context why this is required? What is the use case for it etc.?

Good point! Updated the PR description.

[bill3tt]

In the Thanos UI stores tab, each store already reports the min_time which (I think) comes from Store's InfoResponse RPC. That's the exact piece of information we want to expose here. Is that what your change is exposing here?

In an ideal world, each component that exposes the Store API would expose this information. Users deploy Thanos in all kinds of configuration, it would be useful to have this information available even if they are deploying components other than Store.

[spaparaju]

I believe Min time and Max time are set here, currently do not capture the timestamp of a block that recently got loaded. This comment confirms this observation.

[yeya24]

LGTM