Recovery of 640 MB of log data recovered by RAMCloud 35d8b. All cases are using an in-memory replica unless the legend hints otherwise.

Left to right the dots correspond to 8192, 4096, 2048, 1024, 512, 256, and 128 B objects.

RPC Count: RPCs during recovery for 1 backup is almost exactly 5 * segment count ignoring RPCs for client tablet map refreshes (80 segments here so 400 RPCs).

MasterServer::recoverSegment Performance

rabinpoly was discovered to be far too slow to use as our checksum. The attached graph demonstrates the overheads of various checksum routines on a 640MB (80x8MB segment) invocation of recoverSegment as simulated in the RecoverSegmentBenchmark application.

Take aways:

• For small objects, either crc32c as we go, or perhaps vmac if we checksum only on close (i.e. do the whole segment in one shot, rather than incrementally).
• For larger objects, it doesn't matter too much.

See the pdf to zoom in: http://fiz.stanford.edu:8081/download/attachments/7798899/recoverSegment_checksums.pdf