nim-leveldb/README.md

leveldb.nim

A self-contained LevelDB wrapper for Nim in a Nim friendly way. Uses git-submodule and nimterop so that no external libraries have to be installed or linked.

Original nim LevelDB wrapper: HERE

Replacing of system library dependency with self-contained C/CPP interoperability by (Codex.Storage)[https://codex.storage]

Usage

Create a database:

   import leveldbstatic
   import options

   var db = leveldb.open("/tmp/mydata")

Read or modify the database content:

   assert db.getOrDefault("nothing", "") == ""

   db.put("hello", "world")
   db.put("bin", "GIF89a\1\0")
   echo db.get("hello")
   assert db.get("hello").isSome()

   var key, val = ""
   for key, val in db.iter():
     echo key, ": ", repr(val)

   db.delete("hello")
   assert db.get("hello").isNone()

Batch writes:

   let batch = newBatch()
   for i in 1..10:
     batch.put("key" & $i, $i)
   batch.delete("bin")
   db.write(batch)

Iterate over subset of database content:

   for key, val in db.iterPrefix(prefix = "key1"):
     echo key, ": ", val
   for key, val in db.iter(seek = "key3", reverse = true):
     echo key, ": ", val

   db.close()

Compiling with optimizations

CMake is used during compilation to determine which of the following optimization options are enabled. You can set the following nim compiler flags to 0 or 1 to override them:

• fdatasync from <unistd.h> --passC:-DHAVE_FDATASYNC=1
• F_FULLSYNC from <fcntl.h> --passC:-DHAVE_FULLFSYNC=1
• O_CLOEXEC from <fcntl.h> --passC:-DHAVE_O_CLOEXEC=1
• crc32c from <crc32c/crc32c.h> --passC:-DHAVE_CRC32C=1
• snappy from <snappy.h> --passC:-DHAVE_SNAPPY=1
• zstd from <zstd.h> --passC:-DHAVE_ZSTD=1

Updating

When you want to update this library to a new version of LevelDB, follow these steps:

• Update LevelDB submodule to new version.
• Run 'build.sh'.
• Run 'nimble build' and 'nimble test'.
• Make sure everything's working.
• Increment version of this library in 'leveldbstatic.nimble'.
• Commit the changes.
• Tag the commit with the new version number.
• Push.