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https://github.com/chjj/lcdb

LevelDB implemented in C (unofficial -- not affiliated with Google in any way)
https://github.com/chjj/lcdb

c database leveldb lsm

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LevelDB implemented in C (unofficial -- not affiliated with Google in any way)

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README 

        
# lcdb



_DISCLAIMER: lcdb has **no** affiliation with or endorsement from Google Inc.

whatsoever despite the API prefix being `ldb_` (let's hope they don't [cease

and desist][cad] us again)._



A state-of-the-art database in C89 (originally designed by Jeffrey Dean and

Sanjay Ghemawat and [implemented in C++][ldb]).



## Background



[LevelDB][ldb] was _painstakingly_ ported from C++ to C89¹ for use with [mako].

_mako_ is a C project which requires an LSM tree for its UTXO database (which

in turn requires high write throughput with very effective compaction). _mako_

has a strict development policy of "do not link to libstdc++" and "do not

require a c++ compiler".



LevelDB is used by many bitcoin implementations for indexing the UTXO state.

After experimenting with various databases written in C, it was clear that

LevelDB was still the obvious choice, despite it being written in C++. Existing

databases written in C weren't cutting it in terms of performance (in some

cases maybe they were, but instead lacked effective compaction).



_mako_'s strict policy of portability plus the lack of a production-ready LSM

tree written in C ultimately led to the creation of _lcdb_.



1. Note that the platform (or user) must still provide a working ``

as a build dependency.



### Portability



Portability is one of _lcdb_'s primary goals. _lcdb_ is written in such a way

that it should be usable on Windows 9x¹ as well as unices which predate

POSIX.1-2001.



Portability to this degree was achieved by sifting through copies of MSDN from

the '90s, as well as examining header files from old unix releases to see which

system calls were truly² available in practice.



_lcdb_ also offers the option to build without pthread support (with compaction

taking place on the main thread).



1. Unfortunately, kernel32.dll on Windows 9x does not provide `MoveFileEx`

which is necessary for atomic renames. This means _lcdb_ will be more prone to

recovery errors on Windows 95/98/ME.



2. A good example of the incongruence between standards and implementation is

`fdatasync(2)` and `pread(2)`. The former was standardized by POSIX.1b (1993)

and made mandatory by SUSv2 (1997) and POSIX.1-2001. The latter was

standardized by SUSv2 (1997) and mandated by POSIX.1-2008. In spite of this,

some conforming OSes only began providing them in the last decade (in some

cases the past 5 years or so).



### Cross Compilation



Due to its portability, _lcdb_ is well-suited for common cross-compilation

environments like mingw and wasi-sdk.



This repo includes some helper scripts for both mingw and wasi.



Building with mingw:



``` sh

$ ./scripts/mingw-cmake cmake . -DCMAKE_BUILD_TYPE=Release

$ make

```



Building with wasi-sdk:



``` sh

$ ./scripts/wasi-cmake cmake . -DCMAKE_BUILD_TYPE=Release

$ make

```



## More Disclaimers & License Info



Despite being written in another language, _lcdb_'s codebase is largely

derivative of LevelDB's. As such, the LevelDB license must be shipped (and

conformed to) with the distribution of lcdb in every form.



_lcdb_ is still very immature and is not yet battle-hardened like LevelDB. It

will also likely be subject to breaking ABI changes in the near future. Use at

your own risk.



## Usage



The API tries to mimic the C++ API as much as it can. Users of LevelDB should

find it familiar.



Example:



``` c

#include 

#include 



int main(void) {

  ldb_dbopt_t opt = *ldb_dbopt_default;

  ldb_slice_t key, val, ret;

  ldb_t *db;

  int rc;



  opt.create_if_missing = 1;



  rc = ldb_open("tmp", &opt, &db);



  assert(rc == LDB_OK);



  key = ldb_string("hello");

  val = ldb_string("world");



  rc = ldb_put(db, &key, &val, 0);



  assert(rc == LDB_OK);



  rc = ldb_get(db, &key, &ret, 0);



  assert(rc == LDB_OK);

  assert(ldb_compare(db, &ret, &val) == 0);



  ldb_free(ret.data);

  ldb_close(db);



  return 0;

}

```



Build with:



``` sh

$ cc -o example example.c -llcdb

```



Or:



``` sh

$ cc -o example -I./include example.c liblcdb.a -lpthread

```



See the [header file][h] for more information.



## Contribution and License Agreement



If you contribute code to this project, you are implicitly allowing your code

to be distributed under the MIT license. You are also implicitly verifying that

all code is your original work. ``



## License



- Copyright (c) 2022, Christopher Jeffrey (MIT License).



Parts of this software are based on [google/leveldb][ldb]:



- Copyright (c) 2011, The LevelDB Authors. All rights reserved.



Parts of this software are based on [google/crc32c][crc32c]:



- Copyright (c) 2017, The CRC32C Authors.



Parts of this software are based on [golang/snappy][snappy]:



- Copyright (c) 2011 The Snappy-Go Authors. All rights reserved.



See [LICENSE] for more info.



[cad]: https://github.com/Level/community/issues/66

[ldb]: https://github.com/google/leveldb

[h]: https://github.com/chjj/lcdb/blob/master/include/lcdb.h

[crc32c]: https://github.com/google/crc32c

[snappy]: https://github.com/golang/snappy

[mako]: https://github.com/chjj/mako

[LICENSE]: https://github.com/chjj/lcdb/blob/master/LICENSE