ceremonyclient/pebble/internal/batchskl

batchskl

Fast, non-concurrent skiplist implementation in Go that supports forward and backward iteration.

Limitations

• The interface is tailored for use in indexing pebble batches. Keys and values are stored outside of the skiplist making the skiplist awkward for general purpose use.
• Deletion is not supported. Instead, higher-level code is expected to add deletion tombstones and needs to process those tombstones appropriately.

Pedigree

This code is based on Andy Kimball's arenaskl code.

The arenaskl code is based on the skiplist found in Badger, a Go-based KV store:

https://github.com/dgraph-io/badger/tree/master/skl

The skiplist in Badger is itself based on a C++ skiplist built for Facebook's RocksDB:

https://github.com/facebook/rocksdb/tree/master/memtable

Benchmarks

The benchmarks consist of a mix of reads and writes executed in parallel. The fraction of reads is indicated in the run name: "frac_X" indicates a run where X percent of the operations are reads.

name                  time/op
ReadWrite/frac_0      1.03µs ± 2%
ReadWrite/frac_10     1.32µs ± 1%
ReadWrite/frac_20     1.26µs ± 1%
ReadWrite/frac_30     1.18µs ± 1%
ReadWrite/frac_40     1.09µs ± 1%
ReadWrite/frac_50      987ns ± 2%
ReadWrite/frac_60     1.07µs ± 1%
ReadWrite/frac_70      909ns ± 1%
ReadWrite/frac_80      693ns ± 2%
ReadWrite/frac_90      599ns ± 2%
ReadWrite/frac_100    45.3ns ± 3%

Forward and backward iteration are also fast:

name                  time/op
IterNext              4.49ns ± 3%
IterPrev              4.48ns ± 3%