logstorage: support GetTenants low level API

[jiekun]

Describe Your Changes

Expose GetTenants function in logstorage. It provides a way to get the tenants by time range for projects who use logstorage, such as VictoriaTraces.

The implementation is stolen from #417. Only HTTP API related codes are excluded. The HTTP API could be decided in #417 later without blocking this one.

The CHANGELOG was intentionally left blank, as this feature is not exposed to users.

Checklist

The following checks are mandatory:

• My change adheres to VictoriaMetrics contributing guidelines.
• My change adheres to VictoriaMetrics development goals.

[jiekun]

Thanks for the valuable review comments. They're addressed in a273ad4, with an extra unit test for the new function in storage_search.go. PTAL again.

[jiekun]

@dmitryk-dk I'll rebase your branch once this pull request is merged, since there're a lot of changes by review suggestions already.

[jiekun]

Thanks again. The review comments are addressed in f3f2a4b.

PTAL again.

In the mean time, I noticed variable name wgWorkers and wgWorkers.Done() without defer are also used in

VictoriaLogs/lib/logstorage/storage_search.go

Line 1228 in f3f2a4b

var wgWorkers sync.WaitGroup

Let me know if you want it to be renamed to wg and move the wgWorkers.Done() to defer in a different pull request, or together with this pull request.

[valyala]

Thanks again. The review comments are addressed in f3f2a4b.

PTAL again.

In the mean time, I noticed variable name wgWorkers and wgWorkers.Done() without defer are also used in

VictoriaLogs/lib/logstorage/storage_search.go

Line 1228 in f3f2a4b

var wgWorkers sync.WaitGroup

Let me know if you want it to be renamed to wg and move the wgWorkers.Done() to defer in a different pull request, or together with this pull request.

This should be fixed for the sake of consistency. Please fix this in a separate pull request.

[valyala]

@jiekun , thank you for the pull request!