[Haskell-cafe] Map with incremental serialization

[Chris Wong]

On Sat, Oct 11, 2014 at 10:06 AM, Britt Mathis <britt.mathis at gmail.com> wrote:
> "Acid state has two logs on disk, one for events and another for
> checkpoints. " - does this mean that I choose which to do (for
> instance, I want the state to be saved every 10 minutes or so but
> obviously just the events), or does acid-state handle this internally?

It appends events to a journal automatically, but only saves
checkpoints when you explicitly tell it to.

Usually checkpointing happens when the server shuts down
(saveCheckpointAndClose) but you probably want to trigger it manually
every night or so. This process runs in the background, so your
application can stay online while the checkpoint is saved.

Note that saving checkpoints is only an optimization; acid-state can
reconstruct your data from the event log alone. Having a recent
checkpoint does makes startup/recovery faster though, and saves space
on disk.

Hackage is a very prominent user of acid-state. You might like to look
into how they do things.

Chris