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https://github.com/cockroachdb/pebble

RocksDB/LevelDB inspired key-value database in Go
https://github.com/cockroachdb/pebble

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RocksDB/LevelDB inspired key-value database in Go

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README 

        
# Pebble [![Build Status](https://github.com/cockroachdb/pebble/actions/workflows/ci.yaml/badge.svg?branch=master)](https://github.com/cockroachdb/pebble/actions/workflows/ci.yaml) [![GoDoc](https://godoc.org/github.com/cockroachdb/pebble?status.svg)](https://godoc.org/github.com/cockroachdb/pebble) [Coverage](https://storage.googleapis.com/crl-codecover-public/pebble/index.html)



#### [Nightly benchmarks](https://cockroachdb.github.io/pebble/)



Pebble is a LevelDB/RocksDB inspired key-value store focused on

performance and internal usage by CockroachDB. Pebble inherits the

RocksDB file formats and a few extensions such as range deletion

tombstones, table-level bloom filters, and updates to the MANIFEST

format.



Pebble intentionally does not aspire to include every feature in RocksDB and

specifically targets the use case and feature set needed by CockroachDB:



* Block-based tables

* Checkpoints

* Indexed batches

* Iterator options (lower/upper bound, table filter)

* Level-based compaction

* Manual compaction

* Merge operator

* Prefix bloom filters

* Prefix iteration

* Range deletion tombstones

* Reverse iteration

* SSTable ingestion

* Single delete

* Snapshots

* Table-level bloom filters



RocksDB has a large number of features that are not implemented in

Pebble:



* Backups

* Column families

* Delete files in range

* FIFO compaction style

* Forward iterator / tailing iterator

* Hash table format

* Memtable bloom filter

* Persistent cache

* Pin iterator key / value

* Plain table format

* SSTable ingest-behind

* Sub-compactions

* Transactions

* Universal compaction style



***WARNING***: Pebble may silently corrupt data or behave incorrectly if

used with a RocksDB database that uses a feature Pebble doesn't

support. Caveat emptor!



## Production Ready



Pebble was introduced as an alternative storage engine to RocksDB in

CockroachDB v20.1 (released May 2020) and was used in production

successfully at that time. Pebble was made the default storage engine

in CockroachDB v20.2 (released Nov 2020). Pebble is being used in

production by users of CockroachDB at scale and is considered stable

and production ready.



## Advantages



Pebble offers several improvements over RocksDB:



* Faster reverse iteration via backwards links in the memtable's

  skiplist.

* Faster commit pipeline that achieves better concurrency.

* Seamless merged iteration of indexed batches. The mutations in the

  batch conceptually occupy another memtable level.

* L0 sublevels and flush splitting for concurrent compactions out of L0 and

  reduced read-amplification during heavy write load.

* Faster LSM edits in LSMs with large numbers of sstables through use of a

  copy-on-write B-tree to hold file metadata.

* Delete-only compactions that drop whole sstables that fall within the bounds

  of a range deletion.

* Block-property collectors and filters that enable iterators to skip tables,

  index blocks and data blocks that are irrelevant, according to user-defined

  properties over key-value pairs.

* Range keys API, allowing KV pairs defined over a range of keyspace with

  user-defined semantics and interleaved during iteration.

* Smaller, more approachable code base.



See the [Pebble vs RocksDB: Implementation

Differences](docs/rocksdb.md) doc for more details on implementation

differences.



## RocksDB Compatibility



Pebble strives for forward compatibility with RocksDB 6.2.1 (the latest version

of RocksDB used by CockroachDB). Forward compatibility means that a DB generated

by RocksDB 6.2.1 can be upgraded for use by Pebble. Pebble versions in the `v1`

series may open DBs generated by RocksDB 6.2.1. Since its introduction, Pebble

has adopted various backwards-incompatible format changes that are gated behind

new 'format major versions'. The Pebble `master` branch does not support opening

DBs generated by RocksDB. DBs generated by RocksDB may only be used with recent

versions of Pebble after migrating them through format major version upgrades

using previous versions of Pebble. See the below section of format major

versions.



Even the RocksDB-compatible versions of Pebble only provide compatibility with

the subset of functionality and configuration used by CockroachDB. The scope of

RocksDB functionality and configuration is too large to adequately test and

document all the incompatibilities. The list below contains known

incompatibilities.



* Pebble's use of WAL recycling is only compatible with RocksDB's

  `kTolerateCorruptedTailRecords` WAL recovery mode. Older versions of

  RocksDB would automatically map incompatible WAL recovery modes to

  `kTolerateCorruptedTailRecords`. New versions of RocksDB will

  disable WAL recycling.

* Column families. Pebble does not support column families, nor does

  it attempt to detect their usage when opening a DB that may contain

  them.

* Hash table format. Pebble does not support the hash table sstable

  format.

* Plain table format. Pebble does not support the plain table sstable

  format.

* SSTable format version 3 and 4. Pebble does not support version 3

  and version 4 format sstables. The sstable format version is

  controlled by the `BlockBasedTableOptions::format_version` option.

  See [#97](https://github.com/cockroachdb/pebble/issues/97).



## Format major versions



Over time Pebble has introduced new physical file formats.  Backwards

incompatible changes are made through the introduction of 'format major

versions'. By default, when Pebble opens a database, it defaults to the lowest

supported version. In `v1`, this is `FormatMostCompatible`, which is

bi-directionally compatible with RocksDB 6.2.1 (with the caveats described

above).



Databases created by RocksDB or Pebble versions `v1` and earlier must be upgraded

to a compatible format major version before running newer Pebble versions. Newer

Pebble versions will refuse to open databases in no longer supported formats.



To opt into new formats, a user may set `FormatMajorVersion` on the

[`Options`](https://pkg.go.dev/github.com/cockroachdb/pebble#Options)

supplied to

[`Open`](https://pkg.go.dev/github.com/cockroachdb/pebble#Open), or

upgrade the format major version at runtime using

[`DB.RatchetFormatMajorVersion`](https://pkg.go.dev/github.com/cockroachdb/pebble#DB.RatchetFormatMajorVersion).

Format major version upgrades are permanent; There is no option to

return to an earlier format.



The table below outlines the history of format major versions, along with what

range of Pebble versions support that format.



| Name                               | Value | Migration  | Pebble support |

|------------------------------------|-------|------------|----------------|

| FormatMostCompatible               |   1   | No         | v1             |

| FormatVersioned                    |   3   | No         | v1             |

| FormatSetWithDelete                |   4   | No         | v1             |

| FormatBlockPropertyCollector       |   5   | No         | v1             |

| FormatSplitUserKeysMarked          |   6   | Background | v1             |

| FormatSplitUserKeysMarkedCompacted |   7   | Blocking   | v1             |

| FormatRangeKeys                    |   8   | No         | v1             |

| FormatMinTableFormatPebblev1       |   9   | No         | v1             |

| FormatPrePebblev1Marked            |  10   | Background | v1             |

| FormatSSTableValueBlocks           |  12   | No         | v1             |

| FormatFlushableIngest              |  13   | No         | v1, master     |

| FormatPrePebblev1MarkedCompacted   |  14   | Blocking   | v1, master     |

| FormatDeleteSizedAndObsolete       |  15   | No         | v1, master     |

| FormatVirtualSSTables              |  16   | No         | v1, master     |



Upgrading to a format major version with 'Background' in the migration

column may trigger background activity to rewrite physical file

formats, typically through compactions. Upgrading to a format major

version with 'Blocking' in the migration column will block until a

migration is complete. The database may continue to serve reads and

writes if upgrading a live database through

`RatchetFormatMajorVersion`, but the method call will not return until

the migration is complete.



For reference, the table below lists the range of supported Pebble format major

versions for CockroachDB releases.



| CockroachDB release | Earliest supported                 | Latest supported          |

|---------------------|------------------------------------|---------------------------|

| 20.1 through 21.1   | FormatMostCompatible               | FormatMostCompatible      |

| 21.2                | FormatMostCompatible               | FormatSetWithDelete       |

| 21.2                | FormatMostCompatible               | FormatSetWithDelete       |

| 22.1                | FormatMostCompatible               | FormatSplitUserKeysMarked |

| 22.2                | FormatMostCompatible               | FormatPrePebblev1Marked   |

| 23.1                | FormatSplitUserKeysMarkedCompacted | FormatFlushableIngest     |

| 23.2                | FormatSplitUserKeysMarkedCompacted | FormatVirtualSSTables     |



## Pedigree



Pebble is based on the incomplete Go version of LevelDB:



https://github.com/golang/leveldb



The Go version of LevelDB is based on the C++ original:



https://github.com/google/leveldb



Optimizations and inspiration were drawn from RocksDB:



https://github.com/facebook/rocksdb



## Getting Started



### Example Code



```go

package main



import (

	"fmt"

	"log"



	"github.com/cockroachdb/pebble"

)



func main() {

	db, err := pebble.Open("demo", &pebble.Options{})

	if err != nil {

		log.Fatal(err)

	}

	key := []byte("hello")

	if err := db.Set(key, []byte("world"), pebble.Sync); err != nil {

		log.Fatal(err)

	}

	value, closer, err := db.Get(key)

	if err != nil {

		log.Fatal(err)

	}

	fmt.Printf("%s %s\n", key, value)

	if err := closer.Close(); err != nil {

		log.Fatal(err)

	}

	if err := db.Close(); err != nil {

		log.Fatal(err)

	}

}

```