mirror of
https://github.com/scylladb/scylladb.git
synced 2026-04-20 00:20:47 +00:00
01fb97ee78
There are several reasons we want to do that. One is that it will give us more flexibility in distributing the load. We can subdivide tablets at any points, and achieve more evenly-sized tablets. In particular, we can isolate large partitions into separate tablets. Another reason is vnode-to-tablet migration. We could construct a tablet map which matches exactly the vnode boundaries, so migration can happen transparently from the CQL-coordinator's point of view. Implementation details: We store a vector of tokens which represent tablet boundaries in the tablet_id_map. tablet_id keeps its meaning, it's an index into vector of tablets. To avoid logarithmic lookup of tablet_id from the token, we introduce a lookup structure with power-of-two aligned buckets, and store the tablet_id of the tablet which owns the first token in the bucket. This way, lookup needs to consider tablet id range which overlaps with one bucket. If boundaries are more or less aligned, there are around 1-2 tablets overlapping with a bucket, and the lookup is still O(1). Amount of memory used increased, but not significantly relative to old size (because tablet_info is currently fat): For 131'072 tablets: Before: Size of tablet_metadata in memory: 57456 KiB After: Size of tablet_metadata in memory: 59504 KiB