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1**LevelDB is a fast key-value storage library written at Google that provides an ordered mapping from string keys to string values.**
2
3[![Build Status](https://travis-ci.org/google/leveldb.svg?branch=master)](https://travis-ci.org/google/leveldb)
4[![Build status](https://ci.appveyor.com/api/projects/status/g2j5j4rfkda6eyw5/branch/master?svg=true)](https://ci.appveyor.com/project/pwnall/leveldb)
5
6Authors: Sanjay Ghemawat ([email protected]) and Jeff Dean ([email protected])
7
8# Features
9
10  * Keys and values are arbitrary byte arrays.
11  * Data is stored sorted by key.
12  * Callers can provide a custom comparison function to override the sort order.
13  * The basic operations are `Put(key,value)`, `Get(key)`, `Delete(key)`.
14  * Multiple changes can be made in one atomic batch.
15  * Users can create a transient snapshot to get a consistent view of data.
16  * Forward and backward iteration is supported over the data.
17  * Data is automatically compressed using the [Snappy compression library](http://google.github.io/snappy/).
18  * External activity (file system operations etc.) is relayed through a virtual interface so users can customize the operating system interactions.
19
20# Documentation
21
22  [LevelDB library documentation](https://github.com/google/leveldb/blob/master/doc/index.md) is online and bundled with the source code.
23
24# Limitations
25
26  * This is not a SQL database.  It does not have a relational data model, it does not support SQL queries, and it has no support for indexes.
27  * Only a single process (possibly multi-threaded) can access a particular database at a time.
28  * There is no client-server support builtin to the library.  An application that needs such support will have to wrap their own server around the library.
29
30# Building
31
32This project supports [CMake](https://cmake.org/) out of the box.
33
34### Build for POSIX
35
36Quick start:
37
38```bash
39mkdir -p build && cd build
40cmake -DCMAKE_BUILD_TYPE=Release .. && cmake --build .
41```
42
43### Building for Windows
44
45First generate the Visual Studio 2017 project/solution files:
46
47```cmd
48mkdir build
49cd build
50cmake -G "Visual Studio 15" ..
51```
52The default will build for x86. For 64-bit run:
53
54```cmd
55cmake -G "Visual Studio 15 Win64" ..
56```
57
58To compile the Windows solution from the command-line:
59
60```cmd
61devenv /build Debug leveldb.sln
62```
63
64or open leveldb.sln in Visual Studio and build from within.
65
66Please see the CMake documentation and `CMakeLists.txt` for more advanced usage.
67
68# Contributing to the leveldb Project
69
70The leveldb project welcomes contributions. leveldb's primary goal is to be
71a reliable and fast key/value store. Changes that are in line with the
72features/limitations outlined above, and meet the requirements below,
73will be considered.
74
75Contribution requirements:
76
771. **Tested platforms only**. We _generally_ will only accept changes for
78   platforms that are compiled and tested. This means POSIX (for Linux and
79   macOS) or Windows. Very small changes will sometimes be accepted, but
80   consider that more of an exception than the rule.
81
822. **Stable API**. We strive very hard to maintain a stable API. Changes that
83   require changes for projects using leveldb _might_ be rejected without
84   sufficient benefit to the project.
85
863. **Tests**: All changes must be accompanied by a new (or changed) test, or
87   a sufficient explanation as to why a new (or changed) test is not required.
88
894. **Consistent Style**: This project conforms to the
90   [Google C++ Style Guide](https://google.github.io/styleguide/cppguide.html).
91   To ensure your changes are properly formatted please run:
92
93   ```
94   clang-format -i --style=file <file>
95   ```
96
97## Submitting a Pull Request
98
99Before any pull request will be accepted the author must first sign a
100Contributor License Agreement (CLA) at https://cla.developers.google.com/.
101
102In order to keep the commit timeline linear
103[squash](https://git-scm.com/book/en/v2/Git-Tools-Rewriting-History#Squashing-Commits)
104your changes down to a single commit and [rebase](https://git-scm.com/docs/git-rebase)
105on google/leveldb/master. This keeps the commit timeline linear and more easily sync'ed
106with the internal repository at Google. More information at GitHub's
107[About Git rebase](https://help.github.com/articles/about-git-rebase/) page.
108
109# Performance
110
111Here is a performance report (with explanations) from the run of the
112included db_bench program.  The results are somewhat noisy, but should
113be enough to get a ballpark performance estimate.
114
115## Setup
116
117We use a database with a million entries.  Each entry has a 16 byte
118key, and a 100 byte value.  Values used by the benchmark compress to
119about half their original size.
120
121    LevelDB:    version 1.1
122    Date:       Sun May  1 12:11:26 2011
123    CPU:        4 x Intel(R) Core(TM)2 Quad CPU    Q6600  @ 2.40GHz
124    CPUCache:   4096 KB
125    Keys:       16 bytes each
126    Values:     100 bytes each (50 bytes after compression)
127    Entries:    1000000
128    Raw Size:   110.6 MB (estimated)
129    File Size:  62.9 MB (estimated)
130
131## Write performance
132
133The "fill" benchmarks create a brand new database, in either
134sequential, or random order.  The "fillsync" benchmark flushes data
135from the operating system to the disk after every operation; the other
136write operations leave the data sitting in the operating system buffer
137cache for a while.  The "overwrite" benchmark does random writes that
138update existing keys in the database.
139
140    fillseq      :       1.765 micros/op;   62.7 MB/s
141    fillsync     :     268.409 micros/op;    0.4 MB/s (10000 ops)
142    fillrandom   :       2.460 micros/op;   45.0 MB/s
143    overwrite    :       2.380 micros/op;   46.5 MB/s
144
145Each "op" above corresponds to a write of a single key/value pair.
146I.e., a random write benchmark goes at approximately 400,000 writes per second.
147
148Each "fillsync" operation costs much less (0.3 millisecond)
149than a disk seek (typically 10 milliseconds).  We suspect that this is
150because the hard disk itself is buffering the update in its memory and
151responding before the data has been written to the platter.  This may
152or may not be safe based on whether or not the hard disk has enough
153power to save its memory in the event of a power failure.
154
155## Read performance
156
157We list the performance of reading sequentially in both the forward
158and reverse direction, and also the performance of a random lookup.
159Note that the database created by the benchmark is quite small.
160Therefore the report characterizes the performance of leveldb when the
161working set fits in memory.  The cost of reading a piece of data that
162is not present in the operating system buffer cache will be dominated
163by the one or two disk seeks needed to fetch the data from disk.
164Write performance will be mostly unaffected by whether or not the
165working set fits in memory.
166
167    readrandom  : 16.677 micros/op;  (approximately 60,000 reads per second)
168    readseq     :  0.476 micros/op;  232.3 MB/s
169    readreverse :  0.724 micros/op;  152.9 MB/s
170
171LevelDB compacts its underlying storage data in the background to
172improve read performance.  The results listed above were done
173immediately after a lot of random writes.  The results after
174compactions (which are usually triggered automatically) are better.
175
176    readrandom  : 11.602 micros/op;  (approximately 85,000 reads per second)
177    readseq     :  0.423 micros/op;  261.8 MB/s
178    readreverse :  0.663 micros/op;  166.9 MB/s
179
180Some of the high cost of reads comes from repeated decompression of blocks
181read from disk.  If we supply enough cache to the leveldb so it can hold the
182uncompressed blocks in memory, the read performance improves again:
183
184    readrandom  : 9.775 micros/op;  (approximately 100,000 reads per second before compaction)
185    readrandom  : 5.215 micros/op;  (approximately 190,000 reads per second after compaction)
186
187## Repository contents
188
189See [doc/index.md](doc/index.md) for more explanation. See
190[doc/impl.md](doc/impl.md) for a brief overview of the implementation.
191
192The public interface is in include/leveldb/*.h.  Callers should not include or
193rely on the details of any other header files in this package.  Those
194internal APIs may be changed without warning.
195
196Guide to header files:
197
198* **include/leveldb/db.h**: Main interface to the DB: Start here.
199
200* **include/leveldb/options.h**: Control over the behavior of an entire database,
201and also control over the behavior of individual reads and writes.
202
203* **include/leveldb/comparator.h**: Abstraction for user-specified comparison function.
204If you want just bytewise comparison of keys, you can use the default
205comparator, but clients can write their own comparator implementations if they
206want custom ordering (e.g. to handle different character encodings, etc.).
207
208* **include/leveldb/iterator.h**: Interface for iterating over data. You can get
209an iterator from a DB object.
210
211* **include/leveldb/write_batch.h**: Interface for atomically applying multiple
212updates to a database.
213
214* **include/leveldb/slice.h**: A simple module for maintaining a pointer and a
215length into some other byte array.
216
217* **include/leveldb/status.h**: Status is returned from many of the public interfaces
218and is used to report success and various kinds of errors.
219
220* **include/leveldb/env.h**:
221Abstraction of the OS environment.  A posix implementation of this interface is
222in util/env_posix.cc.
223
224* **include/leveldb/table.h, include/leveldb/table_builder.h**: Lower-level modules that most
225clients probably won't use directly.
226

src/wallet/receive.cpp

src/wallet/coinselection.cpp

src/consensus/validation.h

src/primitives/transaction.cpp

src/script/descriptor.cpp

src/bitcoin-cli.cpp

src/rpc/blockchain.cpp

src/rpc/rawtransaction.cpp

src/init.cpp

src/crypto/sha256.cpp

src/consensus/merkle.h

src/consensus/tx_check.h

src/consensus/tx_verify.h

src/policy/feerate.h

src/policy/feerate.cpp

src/primitives/transaction_identifier.h

src/chainparamsbase.h

src/chainparamsbase.cpp

src/util/moneystr.cpp

src/crypto/ripemd160.h

src/crypto/sha1.h

src/crypto/sha512.h

src/crypto/hmac_sha256.h

src/crypto/hmac_sha512.h

src/crypto/hmac_sha256.cpp

src/crypto/hmac_sha512.cpp

src/crypto/hkdf_sha256_32.h

src/crypto/hkdf_sha256_32.cpp

src/support/cleanse.h

src/support/cleanse.cpp

src/crypto/siphash.cpp

src/crypto/muhash.h

src/crypto/chacha20.h

src/crypto/poly1305.h

src/crypto/chacha20poly1305.h

src/crypto/chacha20poly1305.cpp

src/util/chaintype.cpp

src/util/obfuscation.h

src/util/byte_units.h

src/util/overflow.h

src/blockencodings.cpp

src/net_permissions.cpp

src/policy/packages.cpp

src/policy/rbf.cpp

src/policy/truc_policy.cpp

src/policy/ephemeral_policy.cpp

src/policy/settings.cpp

src/policy/policy.cpp

src/node/transaction.cpp

src/node/coin.cpp

src/rpc/client.cpp

src/rpc/external_signer.cpp

src/rpc/request.cpp

src/rpc/server_util.cpp

src/rpc/fees.cpp

src/rpc/output_script.cpp

src/rpc/rawtransaction_util.cpp

src/rpc/rawtransaction_util.h

src/rpc/register.h

src/rpc/request.h

src/rpc/server_util.h

src/rpc/protocol.h

src/rpc/server.h

src/rpc/signmessage.cpp

src/rpc/txoutproof.cpp

src/rpc/util.cpp

src/rpc/util.h

src/wallet/rpc/addresses.cpp

src/wallet/rpc/backup.cpp

src/wallet/rpc/coins.cpp

src/wallet/rpc/encrypt.cpp

src/wallet/rpc/signmessage.cpp

src/wallet/rpc/util.cpp

src/wallet/rpc/util.h

src/wallet/coincontrol.cpp

src/wallet/coincontrol.h

src/wallet/context.cpp

src/wallet/context.h

src/wallet/crypter.cpp

src/wallet/crypter.h

src/wallet/db.cpp

src/wallet/export.cpp

src/wallet/external_signer_scriptpubkeyman.cpp

src/wallet/rpc/spend.cpp

src/wallet/rpc/transactions.cpp

src/wallet/rpc/wallet.cpp

src/wallet/feebumper.cpp

src/wallet/feebumper.h

src/index/base.h

src/index/base.cpp

src/index/txindex.h

src/index/txindex.cpp

src/index/txindex_key.h

src/index/txospenderindex.h

src/index/txospenderindex.cpp

src/index/blockfilterindex.h

src/index/blockfilterindex.cpp

src/index/coinstatsindex.h

src/index/coinstatsindex.cpp

src/index/db_key.h

src/index/disktxpos.h

src/kernel/chain.cpp

src/kernel/chain.h

src/kernel/checks.cpp

src/kernel/checks.h

src/kernel/context.cpp

src/kernel/context.h

src/kernel/cs_main.cpp

src/kernel/cs_main.h

src/kernel/disconnected_transactions.cpp

src/kernel/disconnected_transactions.h

src/kernel/mempool_removal_reason.cpp

src/kernel/mempool_removal_reason.h

src/kernel/coinstats.cpp

src/kernel/coinstats.h

src/kernel/chainparams.cpp

src/kernel/chainparams.h

src/wallet/sqlite.cpp

src/wallet/sqlite.h

src/wallet/transaction.cpp

src/wallet/transaction.h

src/wallet/dump.cpp

src/wallet/dump.h

src/wallet/init.cpp

src/wallet/walletutil.cpp

src/wallet/walletutil.h

src/wallet/wallettool.cpp

src/wallet/wallettool.h

src/wallet/export.h

src/wallet/migrate.cpp

src/wallet/migrate.h

src/wallet/db.h

src/wallet/walletdb.cpp

src/wallet/interfaces.cpp

src/wallet/scriptpubkeyman.cpp

src/wallet/scriptpubkeyman.h

src/kernel/bitcoinkernel.cpp

src/kernel/bitcoinkernel.h

src/kernel/bitcoinkernel_wrapper.h

src/node/chainstate.cpp

src/node/chainstate.h

src/node/blockstorage.cpp

src/node/blockstorage.h

src/node/mempool_persist.cpp

src/node/mempool_persist.h

src/node/utxo_snapshot.cpp

src/node/utxo_snapshot.h

src/node/kernel_notifications.cpp

src/node/kernel_notifications.h

src/node/blockmanager_args.cpp

src/kernel/blockmanager_opts.h

src/util/expected.cpp

src/policy/settings.h

src/util/types.h

src/kernel/messagestartchars.h

src/kernel/warning.h

src/util/exception.h

src/common/license_info.h

src/node/coins_view_args.h

src/node/database_args.h

src/util/batchpriority.h

src/util/ui_change_type.h

src/node/coins_view_args.cpp

src/node/peerman_args.h

src/util/serfloat.h

src/node/blockmanager_args.h

src/node/database_args.cpp

src/util/overloaded.h

src/interfaces/types.h

src/node/chainstatemanager_args.h

src/node/minisketchwrapper.h

src/util/macros.h

src/util/syserror.h

src/common/run_command.h

src/util/bytevectorhash.cpp

src/node/mempool_persist_args.cpp

src/util/exec.h

src/util/rbf.h

src/crypto/hex_base.h

src/node/mempool_persist_args.h

src/interfaces/echo.h

src/util/any.h

src/util/batchpriority.cpp

src/util/threadnames.h

src/node/coin.h

src/node/mempool_args.h

src/util/asmap.h

src/util/bytevectorhash.h

src/node/context.cpp

src/util/insert.h

src/util/readwritefile.h

src/node/peerman_args.cpp

src/node/interface_ui.cpp

src/interfaces/handler.h

src/node/mining_args.h

src/util/hasher.cpp

src/common/init.h

src/kernel/mempool_limits.h

src/common/system.h

src/crypto/sha3.h

src/util/threadinterrupt.cpp

src/node/protocol_version.h

src/util/exception.cpp

src/common/messages.h

src/node/connection_types.cpp

src/util/bip32.h

src/common/license_info.cpp

src/util/stdmutex.h

src/common/run_command.cpp

src/util/check.cpp

src/util/golombrice.h

src/node/types.h

src/node/timeoffsets.h

src/util/readwritefile.cpp

src/util/fastrange.h

src/util/signalinterrupt.h

src/util/task_runner.h

src/util/syserror.cpp

src/common/interfaces.cpp

src/common/types.h

src/util/threadinterrupt.h

src/kernel/chainstatemanager_opts.h

src/node/psbt.h

src/policy/ephemeral_policy.h

src/util/trace.h

src/common/url.cpp

src/kernel/mempool_options.h

src/util/serfloat.cpp

src/kernel/notifications_interface.h

src/node/timeoffsets.cpp

src/node/warnings.cpp

src/util/hash_type.h

src/crypto/hex_base.cpp

src/node/eviction.h

src/util/tokenbucket.h

src/crypto/aes.h

src/common/pcp.h

src/util/feefrac.cpp

src/node/transaction.h

src/util/threadnames.cpp

src/common/signmessage.h

src/util/exec.cpp

src/util/signalinterrupt.cpp

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