Data.Acid.Local

AcidState container using a transaction log on disk. The term 'Event' is loosely used for transactions with ACID guarantees. 'Method' is loosely used for state operations without ACID guarantees (see Data.Acid.Core).

Documentation

openLocalState

Arguments

:: (Typeable st, IsAcidic st)

=> st

Initial state value. This value is only used if no checkpoint is found.

-> IO (AcidState st)

Create an AcidState given an initial value.

This will create or resume a log found in the "state/[typeOf state]/" directory.

openLocalStateFrom

Arguments

:: IsAcidic st

=> FilePath

Location of the checkpoint and transaction files.

-> st

Initial state value. This value is only used if no checkpoint is found.

-> IO (AcidState st)

Create an AcidState given a log directory and an initial value.

This will create or resume a log found in directory. Running two AcidState's from the same directory is an error but will not result in dataloss.

prepareLocalState

Arguments

:: (Typeable st, IsAcidic st)

=> st

Initial state value. This value is only used if no checkpoint is found.

-> IO (IO (AcidState st))

Create an AcidState given an initial value.

This will create or resume a log found in the "state/[typeOf state]/" directory. The most recent checkpoint will be loaded immediately but the AcidState will not be opened until the returned function is executed.

prepareLocalStateFrom

Arguments

:: IsAcidic st

=> FilePath

Location of the checkpoint and transaction files.

-> st

Initial state value. This value is only used if no checkpoint is found.

-> IO (IO (AcidState st))

Create an AcidState given an initial value.

This will create or resume a log found in directory. The most recent checkpoint will be loaded immediately but the AcidState will not be opened until the returned function is executed.

scheduleLocalUpdate' :: UpdateEvent event => LocalState (EventState event) -> event -> MVar (EventResult event) -> IO (IO ())

Same as scheduleLocalUpdate but does not immediately change the localCopy and return the result mvar - returns an IO action to do this instead. Take care to run actions of multiple Updates in the correct order as otherwise Queries will operate on outdated state.

scheduleLocalColdUpdate' :: LocalState st -> Tagged ByteString -> MVar ByteString -> IO (IO ())

Same as scheduleLocalColdUpdate but does not immediately change the localCopy and return the result mvar - returns an IO action to do this instead. Take care to run actions of multiple Updates in the correct order as otherwise Queries will operate on outdated state.

createCheckpointAndClose :: (SafeCopy st, Typeable st) => AcidState st -> IO ()

Save a snapshot to disk and close the AcidState as a single atomic action. This is useful when you want to make sure that no events are saved to disk after a checkpoint.

data LocalState st

State container offering full ACID (Atomicity, Consistency, Isolation and Durability) guarantees.

Atomicity

State changes are all-or-nothing. This is what you'd expect of any state variable in Haskell and AcidState doesn't change that.

Consistency

No event or set of events will break your data invariants.

Isolation

Transactions cannot interfere with each other even when issued in parallel.

Durability

Successful transaction are guaranteed to survive system failure (both hardware and software).

Constructors

LocalState

Fields

• localCore :: Core st
• localCopy :: IORef st
• localEvents :: FileLog (Tagged ByteString)
• localCheckpoints :: FileLog Checkpoint
• localLock :: FileLock

data Checkpoint

Constructors

Checkpoint EntryId ByteString

Instances

SafeCopy Checkpoint

Defined in Data.Acid.Local

Methods

version :: Version Checkpoint

kind :: Kind Checkpoint

getCopy :: Contained (Get Checkpoint)

putCopy :: Checkpoint -> Contained Put

internalConsistency :: Consistency Checkpoint

objectProfile :: Profile Checkpoint

errorTypeName :: Proxy Checkpoint -> String