[RFC] Search performance on warm index about opensearch

[reta]

Thanks @sohami

With concurrent segment search, there will be multiple slice threads each working on subset of segments

I think in case of the remote (warm index), this is a blessing and the curse. If the cluster has mix of hot (local) / warm (remote) indices, the single query could keep the index searcher pool busy downloading blocks and not searching, this could impact the queries to hot (regular) indices, we may need to think about separating these thread pools.

Using the hints we can potentially download all the data blocks across different index files or even subset of index files for those fields.

Hints sound like a good idea.

[sohami]

Tagging @msfroh @andrross @ankitkala @mch2 for feedback

[Bukhtawar]

Thanks @sohami
The Lucene work around IO concurrency looks promising enough, thanks for highlighting the change, some of the primitives for warm index would definitely be able to leverage the primitive to optimise query latency. Tagging @abiesps as well to ensure we are able to plan for this change.
I am assuming this is a logical extension to basic primitives from #8891 and similar issues like #9987 where some of the improvements including improving caching management is captured. Thanks for bringing this together.

For the historical query access pattern, we can consider maintaining a state of what blocks have been known to be hot, by taking point in time snapshots of the block metadata to better analyse patterns over time.

[sohami]

I am assuming this is a logical extension to basic primitives from #8891 and similar issues like #9987 where some of the improvements including improving caching management is captured. Thanks for bringing this together.

Thanks for sharing these other issues. Yes some of the things captured in these touch upon the File cache management such as creating tiers within FileCache which operates in SegmentLRU fashion.

For the historical query access pattern, we can consider maintaining a state of what blocks have been known to be hot, by taking point in time snapshots of the block metadata to better analyse patterns over time.

Right which is the block level access frequency mechanism. Or using the hints/query visibility mechanism to understand at field level which index will be used for different queries and downloading those upfront. I think both will be useful for different use cases and providing an option to configure these based on use cases will be helpful.

[sohami]

Thanks @sohami

With concurrent segment search, there will be multiple slice threads each working on subset of segments

I think in case of the remote (warm index), this is a blessing and the curse. If the cluster has mix of hot (local) / warm (remote) indices, the single query could keep the index searcher pool busy downloading blocks and not searching, this could impact the queries to hot (regular) indices, we may need to think about separating these thread pools.

True, other way to avoid such interference is using the dedicated warm nodes for hosting the warm indices. In that case, the threadpools will be separate for hot/warm indices. But agreed for shared setup we will need to look into the isolation between hot/warm from all the different aspects.