Streams
The Streams and interactive transactions feature, which was added in Tarantool version v. 2.10.0, allows two things: sequential processing and interleaving.
Sequential processing: With streams there is a guarantee that the server instance will not handle the next request in a stream until it has completed the previous one.
Interleaving: For example, a series of requests can include «begin for stream #1», «begin for stream #2», «insert for stream #1», «insert for stream #2», «delete for stream #1», «commit for stream #1», «rollback for stream #2».
To work with stream transactions using iproto, the following is required:
- The engine should be vinyl or memtx with mvcc.
- The client is responsible for ensuring that the stream identifier, unsigned integer IPROTO_STREAM_ID, is in the request header. IPROTO_STREAM_ID can be any positive 64-bit number, and should be unique for the connection. If IPROTO_STREAM_ID equals zero, the server instance will ignore it.
Name | Code | Description |
---|---|---|
IPROTO_BEGIN | 0x0e | Begin a transaction in the specified stream |
IPROTO_COMMIT | 0x0f | Commit the transaction in the specified stream |
IPROTO_ROLLBACK | 0x10 | Rollback the transaction in the specified stream |
Code: 0x0e.
Begin a transaction in the specified stream. See stream:begin(). The body is optional and can contain two items:
IPROTO_TIMEOUT is an optional timeout (in seconds). After it expires, the transaction will be rolled back automatically.
Suppose that the client has started a stream with the net.box module
net_box = require('net.box')
conn = net_box.connect('localhost:3302')
stream = conn:new_stream()
В этот момент объект stream
будет выглядеть так же, как объект conn
, но включать один дополнительный элемент: stream_id
. Пусть теперь клиент, используя stream
вместо conn
, отправит два запроса:
stream.space.T:insert{1}
stream.space.T:insert{2}
Заголовок и тело этих запросов будут такими же, как в обычных запросах IPROTO_INSERT, но заголовок будет содержать дополнительный элемент IPROTO_STREAM_ID=0x0a
, где MP_UINT=0x01
. В этом примере значение IPROTO_STREAM_ID равно 1, так как при вызове conn:new_stream()
идентификатору каждого нового стрима присваивается уникальное значение, начиная с 1.
The client makes stream transactions by sending, in order:
- IPROTO_BEGIN with an optional transaction timeout in the IPROTO_TIMEOUT field of the request body.
- The transaction data-change and query requests.
- IPROTO_COMMIT or IPROTO_ROLLBACK.
All these requests must contain the same IPROTO_STREAM_ID value.
A rollback will happen automatically if a disconnect occurs or the transaction timeout expires before the commit is possible.
Thus there are now multiple ways to do transactions:
with net_box
stream:begin()
and stream:commit()
or stream:rollback()
which cause IPROTO_BEGIN and IPROTO_COMMIT or IPROTO_ROLLBACK with
the current value of stream.stream_id;
with box.begin() and box.commit() or box.rollback();
with SQL and START TRANSACTION and COMMIT or ROLLBACK.
An application can use any or all of these ways.