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The function can be helpful if you need to access:
all the data in the cluster
a vast number of buckets scattered over the instances in case their individual :ref:`vshard.router.call() <router_api-call>` takes up too much time.
The function is called on the master node of each replica set with the given arguments.
a function to call on the storages (masters of all replica sets)
* ``timeout`` -- a request timeout, in seconds. The timeout is for the entire ``map_callrw()``, including all its stages. * ``return_raw`` -- the :ref:`net.box option <net_box-options>` implemented in Tarantool since version 2.10.0. If set to ``true``, ``net.box`` returns the response data wrapped in a :ref:`MessagePack object <msgpack-object-info>` instead of decoding it to Lua. For more details, see the **Return** section below.
``timeout`` -- a request timeout, in seconds. The timeout is for the entire ``map_callrw()``, including all its stages.
``return_raw`` -- the :ref:`net.box option <net_box-options>` implemented in Tarantool since version 2.10.0. If set to ``true``, ``net.box`` returns the response data wrapped in a :ref:`MessagePack object <msgpack-object-info>` instead of decoding it to Lua. For more details, see the **Return** section below.
Do not use a big timeout (longer than 1 minute, for instance). The router tries to block the bucket moves to another storage for the given timeout on all storages. On failure, the block remains for the entire timeout.
On success: a map with replica set UUIDs (keys) and results of the ``function_name`` (values).
{uuid1 = {res1}, uuid2 = {res2}, ...}
If the function returns ``nil`` or ``box.NULL`` from one of the storages, it will not be present in the resulting map.
If the ``return_raw`` option is used, the result is a map of the following format: ``{[replicaset_uuid] = msgpack.object}`` where ``msgpack.object`` is an object that stores a MessagePack array with the results returned from the storage map function.
The option use case is the same as in using ``net.box``: to avoid decoding of the call results into Lua. The option can be helpful if a router is used as a proxy and results received from a storage are big.
Example:
local res = vshard.router.map_callrw('my_func', args, {..., return_raw = true})

for replicaset_uuid, msgpack_value in pairs(res) do
log.info('Replicaset %s returned %s', replicaset_uuid,
msgpack_value:decode())
end
This is an illustration of the option usage. Normally, you don't need to use ``return_raw`` if you call the :ref:`decode() <msgpack-decode_string>` function.
On failure: ``nil``, error object, and optional replica set UUID where the error occurred. UUID will not be returned if the error is not related to a particular replica set. For instance, the method fails if not all buckets were found, even if all replica sets were scanned successfully. Handling the result looks like this:
res, err, uuid = vshard.router.map_callrw(...)
if not res then
-- Error.
-- 'err' - error object. 'uuid' - optional UUID of replica set
-- where the error happened.
...
else
-- Success.
for uuid, value in pairs(res) do
...
end
end
If the ``return_raw`` option is used, the result on failure is the same as described above.
Map-Reduce in vshard can be divided into three stages: Ref, Map, and Reduce.
**Ref and Map**. ``map_callrw()`` combines both the Ref and the Map stages. The Ref stage ensures data consistency while executing the user's function (``function_name``) on all nodes. Keep in mind that consistency is incompatible with rebalancing (it breaks data consistency). Map-reduce and rebalancing are mutually exclusive, they compete for the cluster time. Any bucket move makes the sender and receiver nodes inconsistent, so it is impossible to call a function on them to access all the data without :ref:`vshard.storage.bucket_ref() <storage_api-bucket_ref>`. It makes the Ref stage intricate, as it should work together with the rebalancer to ensure they do not block each other.
For this, the storage has a special scheduler for bucket moves and storage refs. Storage ref is a volatile counter defined on each instance. It is incremented when a map-reduce request comes and decremented when it ends. Storage ref pins the entire instance with all its buckets, not just a single bucket (like bucket ref).
The scheduler shares storage time between bucket moves and storage refs fairly. The distribution depends on how long and frequent the moves and refs are. It can be configured using the storage options ``sched_move_quota`` and ``sched_ref_quota``. Keep in mind that the scheduler configuration may affect map-reduce requests if used during rebalancing.
During the Map stage, ``map_callrw()`` sends map requests one by one to many servers. On success, the function returns a map. The map is a set of "key—value" pairs. The keys are replica set UUIDs, and the values are the results of the user's function—``function_name``.
**Reduce**. The Reduce stage is not performed by vshard. It is what the user's code does with the results of ``map_callrw()``.
``map_callrw()`` works only on masters. Therefore, you can't use it if at least one replica set has its master node down.
Return the replica set object for the bucket with the specified bucket id value.
a replica set object
replicaset = vshard.router.route(123)
Return all available replica set objects.

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testing_project / Documentation: reference/reference_rock/vshard/vshard_router — English

local res = vshard.router.map_callrw('my_func', args, {..., return_raw = true})

for replicaset_uuid, msgpack_value in pairs(res) do
log.info('Replicaset %s returned %s', replicaset_uuid,
msgpack_value:decode())
end
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python-format, read-only
String age
a year ago
Last updated
a year ago
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