mirror of
https://github.com/element-hq/synapse.git
synced 2024-11-25 02:55:46 +03:00
71 lines
3 KiB
Markdown
71 lines
3 KiB
Markdown
# Background update controller callbacks
|
|
|
|
Background update controller callbacks allow module developers to control (e.g. rate-limit)
|
|
how database background updates are run. A database background update is an operation
|
|
Synapse runs on its database in the background after it starts. It's usually used to run
|
|
database operations that would take too long if they were run at the same time as schema
|
|
updates (which are run on startup) and delay Synapse's startup too much: populating a
|
|
table with a big amount of data, adding an index on a big table, deleting superfluous data,
|
|
etc.
|
|
|
|
Background update controller callbacks can be registered using the module API's
|
|
`register_background_update_controller_callbacks` method. Only the first module (in order
|
|
of appearance in Synapse's configuration file) calling this method can register background
|
|
update controller callbacks, subsequent calls are ignored.
|
|
|
|
The available background update controller callbacks are:
|
|
|
|
### `on_update`
|
|
|
|
_First introduced in Synapse v1.49.0_
|
|
|
|
```python
|
|
def on_update(update_name: str, database_name: str, one_shot: bool) -> AsyncContextManager[int]
|
|
```
|
|
|
|
Called when about to do an iteration of a background update. The module is given the name
|
|
of the update, the name of the database, and a flag to indicate whether the background
|
|
update will happen in one go and may take a long time (e.g. creating indices). If this last
|
|
argument is set to `False`, the update will be run in batches.
|
|
|
|
The module must return an async context manager. It will be entered before Synapse runs a
|
|
background update; this should return the desired duration of the iteration, in
|
|
milliseconds.
|
|
|
|
The context manager will be exited when the iteration completes. Note that the duration
|
|
returned by the context manager is a target, and an iteration may take substantially longer
|
|
or shorter. If the `one_shot` flag is set to `True`, the duration returned is ignored.
|
|
|
|
__Note__: Unlike most module callbacks in Synapse, this one is _synchronous_. This is
|
|
because asynchronous operations are expected to be run by the async context manager.
|
|
|
|
This callback is required when registering any other background update controller callback.
|
|
|
|
### `default_batch_size`
|
|
|
|
_First introduced in Synapse v1.49.0_
|
|
|
|
```python
|
|
async def default_batch_size(update_name: str, database_name: str) -> int
|
|
```
|
|
|
|
Called before the first iteration of a background update, with the name of the update and
|
|
of the database. The module must return the number of elements to process in this first
|
|
iteration.
|
|
|
|
If this callback is not defined, Synapse will use a default value of 100.
|
|
|
|
### `min_batch_size`
|
|
|
|
_First introduced in Synapse v1.49.0_
|
|
|
|
```python
|
|
async def min_batch_size(update_name: str, database_name: str) -> int
|
|
```
|
|
|
|
Called before running a new batch for a background update, with the name of the update and
|
|
of the database. The module must return an integer representing the minimum number of
|
|
elements to process in this iteration. This number must be at least 1, and is used to
|
|
ensure that progress is always made.
|
|
|
|
If this callback is not defined, Synapse will use a default value of 100.
|