allow override parquet queryable block store via header

[yeya24]

What this PR does:

This PR allows override block store to query in parquet queryable via HTTP header X-Cortex-BlockStore-Type. It can be set to either tsdb or parquet. If tsdb, it forces to query store gateway (TSDB). If parquet, it forces to query parquet blocks if possible + tsdb blocks if missing.

This can be useful for rollout and it can be enabled per request basis to test parquet storage. Note that this is block store switch is only available for Instant and Range query API as we have our own query handlers there. It is not available for labels API today.

Which issue(s) this PR fixes:
Fixes #

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[harry671003]

Should the switching logic be for switching between ParquetQueryable or BlockStoreQueryable?

Maybe we need to wrap both queryables into another queryable which will do the switch between both.

func (q *queryable) Select(ctx) {
  blockStoreType := getBlockStoreType(ctx, q.defaultBlockStoreType)
  switch blockStoreType {
    case parquet:
      return q.parquetQueryable.Select(ctx)
    case block:
      return q.blockStoreQueryable.Select(cts)
  }
}

[yeya24]

Should the switching logic be for switching between ParquetQueryable or BlockStoreQueryable? Maybe we need to wrap both queryables into another queryable which will do the switch between both.

The existing parquet queryable is already a wrapper parquetQueryableWithFallback. It already has this selection logic and it basically wraps BlockStoreQueryable and actual parquet queryable from the upstream package https://github.com/prometheus-community/parquet-common/blob/main/search/parquet_queriable.go#L67.

And we cannot simply just fallback to q.parquetQueryable.Select(ctx) fully as we need to query any missing blocks in the time range from Store Gateway, for the scenario in case blocks are still converting to Parquet.

[alanprot]

Thanks.. LGTM