Remove maxMergeAtOnce option from TieredMergePolicy.
#14165
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`maxMergeAtOnce` increases merge amplification by running multiple merges when it could run a single merge, without giving significant benefits in exchange. We removed this parameter for forced merges in apache#230. Let's row remove it for regular merges as well? In practice, merges above the floor segment size will be bounded by the number of segments per tier, and merges below the floor segment size will be unbounded.
mikemccand
approved these changes
Jan 23, 2025
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It is indeed weird to have a separate control (maxMergeAtOnce) from segsPerTier. I think the past motivation was because merging was somewhat RAM heavy, maybe? It allocates stuff for the docid map ... but I think we've improved its ram efficiency, and anyway if that really is somehow a problem, users can lower segsPerTier. Thanks @jpountz.
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maxMergeAtOnceincreases merge amplification by running multiple merges when it could run a single merge, without giving significant benefits in exchange. We removed this parameter for forced merges in #230. Let's row remove it for regular merges as well?In practice, merges above the floor segment size will be bounded by the number of segments per tier, and merges below the floor segment size will be unbounded.