Database.VCache.VTx

Documentation

data VTx a

The VTx transactions allow developers to atomically manipulate PVars and STM resources (TVars, TArrays, etc..). VTx is a thin layer above STM, additionally tracking which PVars are written so it can push the batch to a background writer thread upon commit.

VTx supports full ACID semantics (atomic, consistent, isolated, durable), but durability is optional (see markDurable).

Instances

Alternative VTx

Monad VTx

Functor VTx

MonadPlus VTx

Applicative VTx

runVTx :: VSpace -> VTx a -> IO a

runVTx executes a transaction that may involve both STM TVars (via liftSTM) and VCache PVars (via readPVar, writePVar).

liftSTM :: STM a -> VTx a

run an arbitrary STM operation as part of a VTx transaction.

markDurable :: VTx ()

Durability for a VTx transaction is optional: it requires an additional wait for the background thread to signal that it has committed content to the persistence layer. Due to how writes are batched, a durable transaction may share its wait with many other transactions that occur at more or less the same time.

Developers should mark a transaction durable only if necessary based on domain layer policies. E.g. for a shopping service, normal updates and views of the virtual shopping cart might not be durable while committing to a purchase is durable.

markDurableIf :: Bool -> VTx ()

This variation of markDurable makes it easier to short-circuit complex computations to decide durability when the transaction is already durable. If durability is already marked, the boolean is not evaluated.

getVTxSpace :: VTx VSpace