Currently the cache descriptors store deferreds rather than raw values,
this is a simple way of triggering only one database hit and sharing the
result if two callers attempt to get the same value.
However, there are a few caches that simply store a mapping from string
to string (or int). These caches can have a large number of entries,
under the assumption that each entry is small. However, the size of a
deferred (specifically the size of ObservableDeferred) is signigicantly
larger than that of the raw value, 2kb vs 32b.
This PR therefore changes the cache descriptors to store the raw values
rather than the deferreds.
As a side effect cached storage function now either return a deferred or
the actual value, as the cached list decriptor already does. This is
fine as we always end up just yield'ing on the returned value
eventually, which handles that case correctly.
synapse
This is necessary for replicating the data in synapse to be visible to a
separate service because presence and typing notifications aren't stored
in a database so won't be visible to another process.
This API can be used to either get the raw data by requesting the tables
themselves or to just receive notifications for updates by following the
streams meta-stream.
Returns updates for each table requested a JSON array of arrays with a
row for each row in the table.
Each table is prefixed by a header row with the: name of the table,
current stream_id position for the table, number of rows, number of
columns and the names of the columns.
This is followed by the rows that have been added to the server since
the requester last asked.
The API has a timeout and is hooked up to the notifier so that a slave
can long poll for updates.
Rather than loading them lazily. This allows us to remove all
the yield statements and spurious arguments for the get_next
methods.
It also allows us to replace all instances of get_next_txn with
get_next since get_next no longer needs to access the db.
This is for setting up dependencies that require work on startup. This
is useful for the DataStore that wants to read a bunch from the database
before initiliazing.
Erik Johnston