Make remote snapshot (local)block size configurable #14753
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…tory constructor Signed-off-by: Finn Carroll <[email protected]>
Signed-off-by: Finn Carroll <[email protected]>
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This was referenced Sep 6, 2024
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Description
To perform a search on a remote snapshot we download only the specific blocks of the snapshot needed to complete the search. These blocks have a set 8Mib size and are stored in a local reference counted file cache. The default 8Mib block size has significant disk usage and likely performance implications as there is no mechanism to vary the block size depending on the data we expect to read at runtime.
For example, when lucene opens an index input into a compound file with the intention of only reading the Header, which can be quite small, we will download the entire 8Mib block from our remote snapshot repo.
This is particularly noticeable during snapshot restore, as Lucene downloads various blocks containing metadata for each segment. Lucene keeps this metadata in memory and so the blocks are persistent for the lifetime of the cache and never evicted. By selecting a smaller block size users might drastically reduce the size of their baseline searchable snapshots file cache.
Sample benchmarks.
Related Issues
Feature request issue #14990
Potentially alleviates #11676
Check List
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