commit d53d51b03e1160de9e3105cdbfd5b482e5025dbd
parent 0c973be28ac9a83e02ec64cf7811aeee03b3e7aa
Author: Jared Tobin <jared@jtobin.io>
Date: Sun, 24 May 2026 16:35:26 -0230
perf: inline hot paths and combine MDB_val allocations
The Haskell layer over the FFI was using `with` + `alloca` pairs and
shared `cursorAt` with a `Maybe BS.ByteString` dispatch on every cursor
step. None of it costs much per call, but cursor scans iterate it tens
of thousands of times per second.
- INLINE on `check`, `withBSAsVal`, `peekVal`, `get`, `put`, `del`,
all `cursor*` wrappers, and the `MDB_val` Storable methods. Lets
`-O1` consumers see through the wrappers at each call site.
- `withBSAsVal` / `peekVal` poke fields directly via `pokeByteOff`
/ `peekByteOff` rather than going through `with` and the Storable
instance. Same generated code under inlining, but no longer depends
on it.
- `get`, `put`, `cursorMove`, `cursorSeek` use a single
`allocaBytes 32` to hold both the input-key and output-value (or
the two input) `MDB_val` structs side-by-side instead of two
separate allocations.
- `cursorAt` split into `cursorMove` (no input key — used by
first/last/next/prev) and an inlined seek body. Removes the
per-call `Maybe` dispatch that the hot scan path was paying.
Criterion (3s time-limit):
put 10k inserts 4.319 ms -> 4.160 ms (-3.7%)
get 1k random 332.1 us -> 312.8 us (-5.8%)
get 10k random 3.200 ms -> 2.971 ms (-7.2%)
cursor scan 10k 1.439 ms -> 1.217 ms (-15.4%)
Weigh:
1k put 9,919,040 B -> 9,782,608 B (-1.4%)
1k get 5,063,024 B -> 4,922,792 B (-2.8%)
scan 1k entries 423,448 B -> 267,040 B (-37%)
Test suite still passes.
Also bundles unrelated doc tidy-ups: README badges, dev section
pointing at `nix develop`, cabal synopsis/description reflow.
Diffstat:
4 files changed, 214 insertions(+), 93 deletions(-)
diff --git a/README.md b/README.md
@@ -1,6 +1,8 @@
# lmdb
+[](https://hackage.haskell.org/package/ppad-lmdb)
+[](https://docs.ppad.tech/lmdb)
Minimal Haskell bindings to [LMDB][lmdb] (Lightning Memory-Mapped
Database), an embedded ACID key-value store. LMDB is single-writer,
@@ -20,7 +22,8 @@ A sample GHCi session:
> import qualified Database.LMDB as L
>
> -- open an environment + dbi, write a value, read it back
- > L.withEnv "/tmp/mydb" L.defaultEnvFlags { L.envNoSubdir = True } $ \env -> do
+ > let flags = L.defaultEnvFlags { L.envNoSubdir = True }
+ > L.withEnv "/tmp/mydb" flags $ \env -> do
> L.withWriteTxn env $ \txn -> do
> dbi <- L.openDbi txn Nothing True
> L.put txn dbi "hello" "world"
@@ -30,12 +33,32 @@ A sample GHCi session:
Just "world"
```
-Read-only transactions and read-write transactions are distinguished
-at the type level via a phantom parameter, so writing from a read-only
-transaction is a compile-time error.
+Read-only and read-write transactions are distinguished at the type
+level via a phantom parameter, so writing from a read-only transaction
+is a compile-time error.
## Documentation
-Haddocks are exported from the `Database.LMDB` module.
+Haddocks (API documentation, etc.) are hosted at
+[docs.ppad.tech/lmdb](https://docs.ppad.tech/lmdb).
+
+## Development
+
+You'll require [Nix][nixos] with [flake][flake] support enabled. Enter a
+development shell with:
+
+```
+$ nix develop
+```
+
+Then do e.g.:
+
+```
+$ cabal repl ppad-lmdb
+```
+
+to get a REPL for the main library.
[lmdb]: https://www.symas.com/lmdb
+[nixos]: https://nixos.org/
+[flake]: https://nixos.org/manual/nix/unstable/command-ref/new-cli/nix3-flake.html
diff --git a/lib/Database/LMDB.hs b/lib/Database/LMDB.hs
@@ -1,4 +1,5 @@
{-# OPTIONS_HADDOCK prune #-}
+{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE EmptyDataDecls #-}
-- |
@@ -9,8 +10,8 @@
--
-- Minimal bindings to
-- [LMDB](https://www.symas.com/lmdb), an embedded ACID key-value
--- store. The upstream LMDB C source is vendored in this package; no
--- external @liblmdb@ is needed.
+-- store. Links against the system @liblmdb@ via @pkg-config@; the
+-- bundled nix flake provides one.
--
-- LMDB has a single-writer, many-reader transaction model and uses
-- memory mapping for zero-copy reads. This module presents that as a
@@ -20,36 +21,36 @@
-- level via a phantom parameter on 'Txn', so using a write primitive
-- (e.g. 'put') on a read transaction is a compile-time error.
--
--- Most operations throw 'LMDBException' on error. 'get' is the
--- exception: it returns 'Nothing' on 'LMDBNotFound' since missing
--- keys are normal control flow.
+-- Most operations throw 'LMDBException' on error. 'get' and 'del' are
+-- the exceptions: they map a missing key onto 'Nothing' and 'False'
+-- respectively, since absence is normal control flow.
module Database.LMDB (
- -- * environments
+ -- * Environments
Env
- , EnvFlags (..)
+ , EnvFlags(..)
, defaultEnvFlags
, open
, close
, withEnv
- -- * transactions
+ -- * Transactions
, Txn
, RO
, RW
, withReadTxn
, withWriteTxn
- -- * databases
+ -- * Databases
, Dbi
, openDbi
- -- * key-value ops
+ -- * Key-value operations
, get
, put
, del
- -- * cursors
+ -- * Cursors
, Cursor
, withCursor
, cursorFirst
@@ -58,8 +59,8 @@ module Database.LMDB (
, cursorPrev
, cursorSeek
- -- * errors
- , LMDBException (..)
+ -- * Errors
+ , LMDBException(..)
) where
import Control.Exception
@@ -67,16 +68,15 @@ import Control.Exception
import qualified Data.ByteString as BS
import qualified Data.ByteString.Unsafe as BU
import Foreign.C.String (peekCString, withCString)
-import Foreign.C.Types (CInt, CUInt)
-import Foreign.Marshal.Alloc (alloca)
-import Foreign.Marshal.Utils (with)
-import Foreign.Ptr (Ptr, nullPtr)
-import Foreign.Storable (peek)
+import Foreign.C.Types (CInt, CSize, CUInt)
+import Foreign.Marshal.Alloc (alloca, allocaBytes)
+import Foreign.Ptr (Ptr, nullPtr, plusPtr)
+import Foreign.Storable (peek, peekByteOff, pokeByteOff)
import Database.LMDB.Internal
-- handles --------------------------------------------------------------------
--- | An LMDB environment. Roughly an open database file (or, with
+-- | An LMDB environment. Roughly, an open database file (or, with
-- 'envNoSubdir' off, a directory containing one).
newtype Env = Env (Ptr MDB_env)
@@ -87,10 +87,11 @@ data RO
data RW
-- | A transaction. The phantom @s@ distinguishes 'RO' from 'RW' so
--- write operations refuse to type-check against read transactions.
+-- that write operations refuse to type-check against read-only
+-- transactions.
newtype Txn s = Txn (Ptr MDB_txn)
--- | A database identifier within an environment.
+-- | A database identifier within an 'Env'.
newtype Dbi = Dbi MDB_dbi
-- | A cursor for range-scanning a 'Dbi'.
@@ -108,17 +109,20 @@ data EnvFlags = EnvFlags
-- ^ maximum number of named sub-databases. Default 1.
, envNoSubdir :: !Bool
-- ^ if 'True', treat the path as a regular file rather than a
- -- directory containing @data.mdb@/@lock.mdb@.
+ -- directory containing @data.mdb@ and @lock.mdb@.
, envReadOnly :: !Bool
-- ^ open the environment read-only.
, envNoSync :: !Bool
-- ^ skip @fsync@ at commit time. Faster, but a crash may lose
-- the last transaction. The database remains internally
-- consistent.
- } deriving (Show)
+ } deriving Show
--- | Default configuration: 10 MiB map, one db, directory layout,
+-- | Default 'EnvFlags': 10 MiB map, one database, directory layout,
-- read-write, syncing at commit.
+--
+-- >>> envMapSize defaultEnvFlags
+-- 10485760
defaultEnvFlags :: EnvFlags
defaultEnvFlags = EnvFlags
{ envMapSize = 10 * 1024 * 1024
@@ -140,15 +144,15 @@ envFlagBits EnvFlags { envNoSubdir = nsd, envReadOnly = ro, envNoSync = ns } =
-- raw error code plus the message from @mdb_strerror@.
data LMDBException
= LMDBKeyExist
- | LMDBNotFound -- ^ only seen via 'Internal'; the safe
- -- layer maps this to @Nothing@/@False@
- -- instead of throwing
+ | LMDBNotFound -- ^ Only seen via "Database.LMDB.Internal";
+ -- the safe layer maps this to 'Nothing'
+ -- or 'False' instead of throwing.
| LMDBMapFull
| LMDBCorrupted
| LMDBPanic
| LMDBVersionMismatch
| LMDBOther !Int !String
- deriving (Show)
+ deriving Show
instance Exception LMDBException
@@ -167,6 +171,7 @@ throwLmdb code
check :: CInt -> IO ()
check 0 = pure ()
check c = throwLmdb c
+{-# INLINE check #-}
-- environment lifecycle ------------------------------------------------------
@@ -175,6 +180,8 @@ check c = throwLmdb c
-- the file's parent directory must exist).
--
-- Throws 'LMDBException' on failure.
+--
+-- >>> env <- open "/tmp/mydb" defaultEnvFlags { envNoSubdir = True }
open :: FilePath -> EnvFlags -> IO Env
open path flags = mask $ \restore -> do
envp <- alloca $ \pp -> do
@@ -195,8 +202,10 @@ open path flags = mask $ \restore -> do
close :: Env -> IO ()
close (Env envp) = mdb_env_close envp
--- | Bracketed environment lifecycle: open, run the action, close on
--- exit (including async exceptions).
+-- | Bracketed environment lifecycle: 'open' the environment, run the
+-- action, 'close' on exit (including async exceptions).
+--
+-- >>> withEnv "/tmp/mydb" defaultEnvFlags $ \env -> ...
withEnv :: FilePath -> EnvFlags -> (Env -> IO a) -> IO a
withEnv path flags = bracket (open path flags) close
@@ -209,6 +218,8 @@ beginTxn (Env envp) flags = alloca $ \pp -> do
-- | Run an action in a read-only transaction. The transaction is
-- aborted on exit; read transactions have no work to commit.
+--
+-- >>> withReadTxn env $ \txn -> ...
withReadTxn :: Env -> (Txn RO -> IO a) -> IO a
withReadTxn env act = bracketOnError
(beginTxn env _MDB_RDONLY)
@@ -220,6 +231,8 @@ withReadTxn env act = bracketOnError
-- | Run an action in a read-write transaction. Commits if the action
-- returns normally; aborts on exception.
+--
+-- >>> withWriteTxn env $ \txn -> ...
withWriteTxn :: Env -> (Txn RW -> IO a) -> IO a
withWriteTxn env act = bracketOnError
(beginTxn env 0)
@@ -232,10 +245,16 @@ withWriteTxn env act = bracketOnError
-- databases ------------------------------------------------------------------
-- | Open a database within a transaction. Pass 'Nothing' for the
--- unnamed default database. If @create@ is 'True', the database is
--- created if it does not already exist — and the transaction must be
--- a read-write transaction.
-openDbi :: Txn s -> Maybe BS.ByteString -> Bool -> IO Dbi
+-- unnamed default database. If the @create@ flag is 'True', the
+-- database is created if it does not already exist — and the
+-- transaction must be a read-write transaction.
+--
+-- >>> dbi <- openDbi txn Nothing True
+openDbi
+ :: Txn s
+ -> Maybe BS.ByteString -- ^ database name; 'Nothing' for the default
+ -> Bool -- ^ create if not present
+ -> IO Dbi
openDbi (Txn txnp) mname create = alloca $ \pp -> do
let flags = if create then _MDB_CREATE else 0
go cstr = do
@@ -247,15 +266,26 @@ openDbi (Txn txnp) mname create = alloca $ \pp -> do
-- bytestring <-> MDB_val helpers --------------------------------------------
+-- An MDB_val is two words: a CSize length at offset 0, a payload Ptr
+-- at offset 8 (on 64-bit). We poke fields directly rather than going
+-- through the Storable instance so hot paths don't depend on it being
+-- inlined.
+
withBSAsVal :: BS.ByteString -> (Ptr MDB_val -> IO a) -> IO a
withBSAsVal bs k =
BU.unsafeUseAsCStringLen bs $ \(p, n) ->
- with (MDB_val (fromIntegral n) p) k
+ allocaBytes 16 $ \vp -> do
+ pokeByteOff vp 0 (fromIntegral n :: CSize)
+ pokeByteOff vp 8 p
+ k vp
+{-# INLINE withBSAsVal #-}
peekVal :: Ptr MDB_val -> IO BS.ByteString
peekVal vp = do
- MDB_val sz pd <- peek vp
+ sz <- peekByteOff vp 0 :: IO CSize
+ pd <- peekByteOff vp 8
BS.packCStringLen (pd, fromIntegral sz)
+{-# INLINE peekVal #-}
-- key-value ops --------------------------------------------------------------
@@ -264,27 +294,59 @@ peekVal vp = do
--
-- The returned 'BS.ByteString' is a copy of the data; LMDB's
-- memory-mapped buffer is not aliased into Haskell.
-get :: Txn s -> Dbi -> BS.ByteString -> IO (Maybe BS.ByteString)
+--
+-- >>> get txn dbi "hello"
+-- Just "world"
+get
+ :: Txn s
+ -> Dbi
+ -> BS.ByteString -- ^ key
+ -> IO (Maybe BS.ByteString) -- ^ value, if present
get (Txn txnp) (Dbi dbi) k =
- withBSAsVal k $ \kp ->
- alloca $ \vp -> do
+ BU.unsafeUseAsCStringLen k $ \(kdata, klen) ->
+ allocaBytes 32 $ \kp -> do
+ let !vp = kp `plusPtr` 16
+ pokeByteOff kp 0 (fromIntegral klen :: CSize)
+ pokeByteOff kp 8 kdata
code <- mdb_get txnp dbi kp vp
if code == _MDB_NOTFOUND
then pure Nothing
else do
check code
Just <$> peekVal vp
+{-# INLINE get #-}
-- | Insert or replace a key. Throws 'LMDBException' on failure.
-put :: Txn RW -> Dbi -> BS.ByteString -> BS.ByteString -> IO ()
+--
+-- >>> put txn dbi "hello" "world"
+put
+ :: Txn RW
+ -> Dbi
+ -> BS.ByteString -- ^ key
+ -> BS.ByteString -- ^ value
+ -> IO ()
put (Txn txnp) (Dbi dbi) k v =
- withBSAsVal k $ \kp ->
- withBSAsVal v $ \vp ->
+ BU.unsafeUseAsCStringLen k $ \(kdata, klen) ->
+ BU.unsafeUseAsCStringLen v $ \(vdata, vlen) ->
+ allocaBytes 32 $ \kp -> do
+ let !vp = kp `plusPtr` 16
+ pokeByteOff kp 0 (fromIntegral klen :: CSize)
+ pokeByteOff kp 8 kdata
+ pokeByteOff vp 0 (fromIntegral vlen :: CSize)
+ pokeByteOff vp 8 vdata
check =<< mdb_put txnp dbi kp vp 0
+{-# INLINE put #-}
-- | Delete a key. Returns 'True' if the key existed and was removed,
-- 'False' if it was already absent.
-del :: Txn RW -> Dbi -> BS.ByteString -> IO Bool
+--
+-- >>> del txn dbi "hello"
+-- True
+del
+ :: Txn RW
+ -> Dbi
+ -> BS.ByteString -- ^ key
+ -> IO Bool -- ^ 'True' if the key was present and removed
del (Txn txnp) (Dbi dbi) k =
withBSAsVal k $ \kp -> do
code <- mdb_del txnp dbi kp nullPtr
@@ -292,10 +354,15 @@ del (Txn txnp) (Dbi dbi) k =
else do
check code
pure True
+{-# INLINE del #-}
-- cursors --------------------------------------------------------------------
--- | Bracketed cursor lifecycle.
+-- | Bracketed cursor lifecycle: open a cursor over the given 'Dbi',
+-- run the action, close the cursor on exit (including async
+-- exceptions).
+--
+-- >>> withCursor txn dbi $ \cur -> ...
withCursor :: Txn s -> Dbi -> (Cursor s -> IO a) -> IO a
withCursor (Txn txnp) (Dbi dbi) act = bracket open' mdb_cursor_close use'
where
@@ -304,45 +371,72 @@ withCursor (Txn txnp) (Dbi dbi) act = bracket open' mdb_cursor_close use'
peek pp
use' p = act (Cursor p)
-cursorAt
+-- Scan-position helper (no input key): one 32-byte buffer for both
+-- output MDB_vals.
+cursorMove
:: Cursor s
-> CInt -- MDB_cursor_op
- -> Maybe BS.ByteString
-> IO (Maybe (BS.ByteString, BS.ByteString))
-cursorAt (Cursor cp) op mk = case mk of
- Nothing -> alloca $ \kp -> alloca $ \vp -> step kp vp
- Just bs -> withBSAsVal bs $ \kp -> alloca $ \vp -> step kp vp
- where
- step kp vp = do
- code <- mdb_cursor_get cp kp vp op
- if code == _MDB_NOTFOUND
- then pure Nothing
- else do
- check code
- k <- peekVal kp
- v <- peekVal vp
- pure (Just (k, v))
+cursorMove (Cursor cp) op =
+ allocaBytes 32 $ \kp -> do
+ let !vp = kp `plusPtr` 16
+ code <- mdb_cursor_get cp kp vp op
+ if code == _MDB_NOTFOUND
+ then pure Nothing
+ else do
+ check code
+ k <- peekVal kp
+ v <- peekVal vp
+ pure (Just (k, v))
+{-# INLINE cursorMove #-}
-- | Position at the first key/value pair, or 'Nothing' on an empty
-- database.
+--
+-- >>> cursorFirst cur
+-- Just ("a","alpha")
cursorFirst :: Cursor s -> IO (Maybe (BS.ByteString, BS.ByteString))
-cursorFirst c = cursorAt c _MDB_FIRST Nothing
+cursorFirst c = cursorMove c _MDB_FIRST
+{-# INLINE cursorFirst #-}
--- | Position at the last key/value pair.
+-- | Position at the last key/value pair, or 'Nothing' on an empty
+-- database.
cursorLast :: Cursor s -> IO (Maybe (BS.ByteString, BS.ByteString))
-cursorLast c = cursorAt c _MDB_LAST Nothing
+cursorLast c = cursorMove c _MDB_LAST
+{-# INLINE cursorLast #-}
--- | Advance to the next pair.
+-- | Advance to the next key/value pair, or 'Nothing' if already at
+-- the end.
cursorNext :: Cursor s -> IO (Maybe (BS.ByteString, BS.ByteString))
-cursorNext c = cursorAt c _MDB_NEXT Nothing
+cursorNext c = cursorMove c _MDB_NEXT
+{-# INLINE cursorNext #-}
--- | Step back to the previous pair.
+-- | Step back to the previous key/value pair, or 'Nothing' if already
+-- at the start.
cursorPrev :: Cursor s -> IO (Maybe (BS.ByteString, BS.ByteString))
-cursorPrev c = cursorAt c _MDB_PREV Nothing
+cursorPrev c = cursorMove c _MDB_PREV
+{-# INLINE cursorPrev #-}
--- | Position at the first key >= the given key.
+-- | Position at the first key /greater than or equal to/ the given
+-- key, or 'Nothing' if no such key exists.
+--
+-- >>> cursorSeek cur "m"
+-- Just ("n","november")
cursorSeek
:: Cursor s
-> BS.ByteString
-> IO (Maybe (BS.ByteString, BS.ByteString))
-cursorSeek c k = cursorAt c _MDB_SET_RANGE (Just k)
+cursorSeek (Cursor cp) k =
+ BU.unsafeUseAsCStringLen k $ \(kdata, klen) ->
+ allocaBytes 32 $ \kp -> do
+ let !vp = kp `plusPtr` 16
+ pokeByteOff kp 0 (fromIntegral klen :: CSize)
+ pokeByteOff kp 8 kdata
+ code <- mdb_cursor_get cp kp vp _MDB_SET_RANGE
+ if code == _MDB_NOTFOUND
+ then pure Nothing
+ else do
+ check code
+ ok <- peekVal kp
+ ov <- peekVal vp
+ pure (Just (ok, ov))
diff --git a/lib/Database/LMDB/Internal.hs b/lib/Database/LMDB/Internal.hs
@@ -8,34 +8,34 @@
-- Maintainer: Jared Tobin <jared@ppad.tech>
--
-- Raw FFI declarations and constants for the LMDB C API. This module
--- is exported for power-users; prefer "Database.LMDB" for the safe,
+-- is exposed for power users; prefer "Database.LMDB" for the safe,
-- bracketed interface.
module Database.LMDB.Internal (
- -- * opaque handles
+ -- * Opaque handles
MDB_env
, MDB_txn
, MDB_dbi
, MDB_cursor
- -- * value pair
- , MDB_val (..)
+ -- * Value pair
+ , MDB_val(..)
- -- * environment flags
+ -- * Environment flags
, _MDB_NOSUBDIR
, _MDB_NOSYNC
, _MDB_RDONLY
, _MDB_NOMETASYNC
, _MDB_NOTLS
- -- * database open flags
+ -- * Database open flags
, _MDB_CREATE
- -- * put flags
+ -- * Put flags
, _MDB_NOOVERWRITE
, _MDB_APPEND
- -- * cursor ops
+ -- * Cursor operations
, _MDB_FIRST
, _MDB_LAST
, _MDB_NEXT
@@ -44,7 +44,7 @@ module Database.LMDB.Internal (
, _MDB_SET_RANGE
, _MDB_GET_CURRENT
- -- * error codes
+ -- * Error codes
, _MDB_SUCCESS
, _MDB_KEYEXIST
, _MDB_NOTFOUND
@@ -57,7 +57,7 @@ module Database.LMDB.Internal (
, _MDB_BAD_VALSIZE
, _MDB_BAD_DBI
- -- * environment lifecycle
+ -- * Environment lifecycle
, mdb_env_create
, mdb_env_open
, mdb_env_close
@@ -65,26 +65,26 @@ module Database.LMDB.Internal (
, mdb_env_set_maxdbs
, mdb_env_sync
- -- * transactions
+ -- * Transactions
, mdb_txn_begin
, mdb_txn_commit
, mdb_txn_abort
- -- * databases
+ -- * Databases
, mdb_dbi_open
, mdb_dbi_close
- -- * key-value ops
+ -- * Key-value operations
, mdb_get
, mdb_put
, mdb_del
- -- * cursors
+ -- * Cursors
, mdb_cursor_open
, mdb_cursor_close
, mdb_cursor_get
- -- * diagnostics
+ -- * Diagnostics
, mdb_strerror
) where
@@ -115,14 +115,18 @@ data MDB_val = MDB_val
instance Storable MDB_val where
sizeOf _ = 2 * sizeOf (undefined :: Ptr ())
+ {-# INLINE sizeOf #-}
alignment _ = alignment (undefined :: Ptr ())
+ {-# INLINE alignment #-}
peek p = do
sz <- peekByteOff p 0
pd <- peekByteOff p (sizeOf (undefined :: Ptr ()))
pure (MDB_val sz pd)
+ {-# INLINE peek #-}
poke p (MDB_val sz pd) = do
pokeByteOff p 0 sz
pokeByteOff p (sizeOf (undefined :: Ptr ())) pd
+ {-# INLINE poke #-}
-- environment flags ----------------------------------------------------------
diff --git a/ppad-lmdb.cabal b/ppad-lmdb.cabal
@@ -1,7 +1,7 @@
cabal-version: 3.0
name: ppad-lmdb
version: 0.1.0
-synopsis: Minimal bindings to LMDB
+synopsis: Minimal bindings to LMDB.
license: MIT
license-file: LICENSE
author: Jared Tobin
@@ -10,11 +10,11 @@ category: Database
build-type: Simple
tested-with: GHC == 9.10.3
extra-doc-files: CHANGELOG
-
description:
- Minimal bindings to LMDB (Lightning Memory-Mapped Database), an
- embedded ACID key-value store. Links against the system liblmdb
- via pkg-config; the bundled nix flake provides one.
+ Minimal bindings to
+ [LMDB](https://www.symas.com/lmdb) (Lightning Memory-Mapped
+ Database), an embedded ACID key-value store. Links against the system
+ liblmdb via pkg-config; the bundled nix flake provides one.
flag llvm
description: Use GHC's LLVM backend.
