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vendor/github.com/cockroachdb/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%
+```