ceremonyclient/pebble/internal/batchskl/README.md
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# 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%
```