Description
Store, StateGroupDataStore, DataStore, Storage, DatabasePool, Databases... 🤯
#8033 made some attempts to clean it up, but there's a lot more to do here.
There are basically three layers:
-
a
DatabasePoolrepresents a connection to a physical database. Normally you have exactly one of these, but it's possible to set Synapse up to talk to two separate postgres instances (one of them gets used for state storage (state_groups_state, mainly), and the other for everything else), in which case you have two. -
a
<foo>Storeis a low-level thing containing SQL, and is linked to a singleDatabasePool. We basically have two of these (stateandmain), again with the state/everything else split.stateis always aStateGroupDataStore, butmaincan be any of (DataStore,AdminCmdSlavedStore,GenericWorkerSlavedStore) depending on the synapse app.PersistEventsStoreseems to be a special case, and is a layer over themainstore.Databasesis a singleton which instantiates theDatabasePools and<foo>Stores, and holds references to them. -
a
<foo>Storageis a higher-level thing which spans multiple<foo>Stores. Ideally it does not do any SQL itself, but delegates it all to theStores. We have three of these (PurgeEventsStorage,StateGroupStorage,EventsPersistenceStorage). Note that a lot of non-storage code skips this layer and goes straight to the<foo>Stores.Storageitself instantiates and holds references to the<foo>Storages.Edit 2022/06/06: These are now known as
<foo>StorageControllers, andStorageitself is now known asStorageControllers.
This is all very well, but I seem to be incapable of holding it in my head at once. This is really not helped by there being a lot of inconsistent naming. Examples:
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Databasesshould surely be calledDataStoreManageror similar. AndHomeServer.get_datastores, which returns theDatabases, should be renamed. - Likewise,
Storage->StorageManager. (superceded by Rename storage classes #12913) - the various implementations of the main
Storecould do with being named as such, for consistency withStateGroupDataStore- egMasterMainDataStore,WorkerMainDataStore. -
HomeServer.get_datastore(which returns the mainStore) exists only for backwards compatibility. We should replace it with calls toget_datastores().mainfor consistency with theStateGroupDataStore. RemoveHomeServer.get_datastore()#12031 - All the million places that have a
self.storeshould instead have aself._main_store.