Database.LevelDB

LevelDB Haskell binding.

The API closely follows the C-API of LevelDB. For more information, see: http://leveldb.googlecode.com

Basic example:

 withLevelDB "/tmp/leveldbtest" [CreateIfMissing, CacheSize 1024] $ \db -> do
     put db [] "foo" "bar"
     get db [] "foo" >>= print
     delete db [] "foo"
     get db [] "foo" >>= print

Batch write and iterating:

 withLevelDB "/tmp/leveldbtest" [CreateIfMissing, CacheSize 1024] $ \db -> do
     write db [Sync] [ Put "a" "one"
                     , Put "b" "two"
                     , Put "c" "three" ]
     dumpEntries db []

     where
         dumpEntries db opts =
             withIterator db opts $ \iter -> do
                 iterFirst iter
                 iterEntries iter print

         iterEntries iter f = do
             valid <- iterValid iter
             when valid $ do
                 key <- iterKey iter
                 val <- iterValue iter
                 _   <- f (key, val)
                 _   <- iterNext iter
                 iterEntries iter f

Exported Types

data DB

Database handle

data BatchOp

Batch operation

Constructors

Put ByteString ByteString

Del ByteString

Instances

Show BatchOp

data Compression

Compression setting

Constructors

NoCompression

Snappy

Instances

Eq Compression

Show Compression

data Option

Options when opening a database

Constructors

CreateIfMissing

ErrorIfExists

ParanoidChecks

WriteBufferSize Int

MaxOpenFiles Int

BlockSize Int

BlockRestartInterval Int

UseCompression Compression

CacheSize Int

Instances

Eq Option

Show Option

type Options = [Option]

data ReadOption

Options for read operations

Constructors

VerifyCheckSums

FillCache

UseSnapshot Snapshot

type ReadOptions = [ReadOption]

data Snapshot

Snapshot handle

type WriteBatch = [BatchOp]

data WriteOption

Options for write operations

Constructors

Sync

fsync the rows written immediately

Instances

Show WriteOption

type WriteOptions = [WriteOption]

type Range = (ByteString, ByteString)

Basic Database Manipulation

withLevelDB :: FilePath -> Options -> (DB -> IO a) -> IO a

Run an action on a database

withSnapshot :: DB -> (Snapshot -> IO a) -> IO a

Run an action with a snapshot of the database.

put :: DB -> WriteOptions -> ByteString -> ByteString -> IO ()

Write a key/value pair

delete :: DB -> WriteOptions -> ByteString -> IO ()

Delete a key/value pair

write :: DB -> WriteOptions -> WriteBatch -> IO ()

Perform a batch mutation

get :: DB -> ReadOptions -> ByteString -> IO (Maybe ByteString)

Read a value by key

Administrative Functions

data Property

Properties exposed by LevelDB

Constructors

NumFilesAtLevel Int

Stats

SSTables

Instances

Eq Property

Show Property

getProperty :: DB -> Property -> IO (Maybe ByteString)

Get a DB property

destroy :: FilePath -> Options -> IO ()

Destroy the given leveldb database.

repair :: FilePath -> Options -> IO ()

Repair the given leveldb database.

approximateSize :: DB -> Range -> IO Int64

Inspect the approximate sizes of the different levels

Iteration

data Iterator

Iterator handle

withIterator :: DB -> ReadOptions -> (Iterator -> IO a) -> IO a

Run an action with an Iterator. The iterator will be closed after the action returns or an error is thrown. Thus, the iterator will not be valid after this function terminates.

iterOpen :: DB -> ReadOptions -> IO Iterator

Create an Iterator. Consider using withIterator.

iterClose :: Iterator -> IO ()

Release an Iterator. Consider using withIterator.

iterValid :: Iterator -> IO Bool

An iterator is either positioned at a key/value pair, or not valid. This function returns true iff the iterator is valid.

iterSeek :: Iterator -> ByteString -> IO ()

Position at the first key in the source that is at or past target. The iterator is valid after this call iff the source contains an entry that comes at or past target.

iterFirst :: Iterator -> IO ()

Position at the first key in the source. The iterator is valid after this call iff the source is not empty.

iterLast :: Iterator -> IO ()

Position at the last key in the source. The iterator is valid after this call iff the source is not empty.

iterNext :: Iterator -> IO ()

Moves to the next entry in the source. After this call, iterValid is true iff the iterator was not positioned the last entry in the source.

iterPrev :: Iterator -> IO ()

Moves to the previous entry in the source. After this call, iterValid is true iff the iterator was not positioned at the first entry in the source.

iterKey :: Iterator -> IO ByteString

Return the key for the current entry. The underlying storage for the returned slice is valid only until the next modification of the iterator.

iterValue :: Iterator -> IO ByteString

Return the value for the current entry. The underlying storage for the returned slice is valid only until the next modification of the iterator.