Multi-threading with OrientDB
OrientDB supports multi-threaded access to the database, but only through one instance per thread. That is, ODatabase* and OrientGraph* instances are not thread-safe. You must only use one instance per thread and only use each instance in one thread at a time.
The ODocument, OrientVertex and OrientEdge classes are also not thread-safe. So, sharing them across threads can lead to unexpected errors that may prove difficult to recognize.
For more information, see Concurrency.
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| Beginning in version 2.1 of OrientDB, implicit usage of multiple database instances from the same thread is no longer allowed. Any attempt to manage multiple instances in the same thread must explicitly call the db.activateOnCurrentThread() method against the database instance before you use it.|
Understanding Multi-threading
Multiple database instances point to the same storage through the same database URL. In this case, Storage is thread-safe and orchestrates requests from different ODatabase* instances.
ODatabaseDocumentTx-1-----+
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+-----> OStorage(url=plocal:/tmp/db)
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ODatabaseDocumentTx-2-----+
The same goes for the Graph API,
OrientGraph-1------------+
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+------> OStorage(url=plocal:/tmp/db)
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OrientGraph-2------------+
Shared Objects
Individual database instances share the following objects:
- Schema
- Index Manager
- Security
For concurrnet contexts these objects synchronize by storing the current database in the ThreadLocal variable. Whenever you create, open or acquire a database connection the instance is automatically set to the current ThreadLocal space. Meaning that, in normal usage, this operation remains hidden from the developer.
OrientDB always resets the current database for all common operatings, such as load, save, and so on.