Feature #18961

Updated by Peter Amstutz 5 months ago

Use the following strategy for prefetch: 

 When a read happens on a file, look at the next N blocks the make up the _manifest stream_ and issue prefetch requests for those blocks.    These blocks get loaded into the cache so they are ready to go when they are needed. 

 By looking ahead in the stream rather than just the file, this also works for manifests containing small files which are stored as 1 block per file. 

 There should be a config knob to control how much data or blocks are prefetched so that sites can experiment with optimal throughput. 

 This implies the cache behavior needs to support pre-fetch, which means pre-fetched blocks should not push out actively used blocks but should be able to push out less recently used blocks.    Plain LRU behavior where a block is promoted each time it is accessed may be sufficient but metrics will be helpful.