This patch adds a write optimizer to LSSnapshot. The optimizer is only used when
there are no observers for other content processes.
Differential Revision: https://phabricator.services.mozilla.com/D31199
This patch renames the Checkpoint IPC message to CheckpointAndNotify. Other structures used by checkpointing are renamed too. Datastore methods SetItem/RemoveItem/Clear no longer call NotifyObservers, it's now up to RecvCheckpointAndNotify to call it.
Differential Revision: https://phabricator.services.mozilla.com/D31197
This improves performance by keeping snapshots around for some time if there are no changes done by other processes. If a snapshot is not destroyed immediately after getting into the stable state then there's a chance that it won't have to be synchronously created again when a new opeartion is requested.
Before this patch, it was only possible to initialize a snapshot to the Partial state or AllOrderedItems state. Now there's a third state AllOrderedKeys.
This improves performance by eliminating sync calls to parent process when we know nothing about a key in content process (in that case we have to use a sync call to the parent process to see if there's a value for it).
With this patch we always try to send all keys to content when a snapshot is being initialized. For this to work efficiently, we cache the size of all keys.
Having cached size of all keys also allows us to just iterate the mValues hashtable when the size of keys is bigger than snapshot prefill threshold (instead of iterating over the mKeys array and joining with mValues for each particular key).
There's some additional cleanup in snapshot info construction and Datastore::SetItem/RemoveItem/Clear methods.
There's now an upper limit for snapshot prefilling. The value is configurable and is currently set to 4096 bytes.
Snapshots can operate in multiple modes depending on if all items have been loaded or all keys have been received. This should provide the best performance for each specific state.
This patch also adds support for creating explicit snapshots which can be used for testing.
This improves performance a lot in cases when multiple operations are invoked by a single JS function (number of sync IPC calls is reduced to a minimum). It also improves correctness since changes are not visible to other content processes until a JS function finishes.
The patch implements core infrastructure, all items are sent to content when a snapshot is initialized and everything is fully working. However, sending of all items at once is not optimal for bigger databases. Support for lazy loading of items is implemented in a following patch.
