Sort Rows by Series when flushing to disk

[cyriltovena]

Currently we don't sort across row groups of profiles when flushing all of them.

I believe we should be able to stream all row groups from

phlare/pkg/phlaredb/profile_store.go

Line 360 in b67c811

func (s *profileStore) writeRowGroups(path string, rowGroups []parquet.RowGroup) (n uint64, numRowGroups uint64, err error) {

and reorder them by SeriesID then timestamp.

[simonswine]

This will improve data locality a ton, but I am a bit unsure how this will impact querying, as the order of querying will be:

• Timestamp first then SeriesID

And blocks will be strictly stored in

• SeriesID first then Timestamp

Currently the sorting is more like:

• Within a single row group strictly: Series first then Timestamp
• Across row groups, loosely timestamp ordered

If we query a time range only impacting a part of the ~3 hours within a block, we could get away by only reading pages that fall within the time ranges (based on the pages Min/Max). With this change we can only access pages by their SeriesIDs min/max. I don't expect a major issue, I am just wondering.

Fairly relevant to the change in #799

[simonswine]

Maybe we need to address our query behaviour to use the order that is in the blocks as well.