NAME
AI::MXNet::KVStore - Key value store interface of MXNet.
DESCRIPTION
Key value store interface of MXNet for parameter synchronization, over multiple devices.
init
Initialize a single or a sequence of key-value pairs into the store.
For each key, one must init it before push and pull.
Only worker 0's (rank == 0) data are used.
This function returns after data have been initialized successfully
Parameters
----------
key : int or an array ref of int
The keys.
value : NDArray or an array ref of NDArray objects
The values.
Examples
--------
>>> # init a single key-value pair
>>> $shape = [2,3]
>>> $kv = mx->kv->create('local')
>>> $kv->init(3, mx->nd->ones($shape)*2)
>>> $a = mx->nd->zeros($shape)
>>> $kv->pull(3, out=>$a)
>>> print $a->aspdl
[[ 2 2 2]
[ 2 2 2]]
>>> # init a list of key-value pairs
>>> $keys = [5, 7, 9]
>>> $kv->init(keys, [map { mx->nd->ones($shape) } 0..@$keys-1])
push
Push a single or a sequence of key-value pairs into the store.
Data consistency:
1. this function returns after adding an operator to the engine.
2. push is always called after all previous push and pull on the same
key are finished.
3. there is no synchronization between workers. One can use _barrier()
to sync all workers.
Parameters
----------
key : int or array ref of int
value : NDArray or array ref of NDArray or array ref of array refs of NDArray
priority : int, optional
The priority of the push operation.
The higher the priority, the faster this action is likely
to be executed before other push actions.
Examples
--------
>>> # push a single key-value pair
>>> $kv->push(3, mx->nd->ones($shape)*8)
>>> $kv->pull(3, out=>$a) # pull out the value
>>> print $a->aspdl()
[[ 8. 8. 8.]
[ 8. 8. 8.]]
>>> # aggregate the value and the push
>>> $gpus = [map { mx->gpu($_) } 0..3]
>>> $b = [map { mx->nd->ones($shape, ctx => $_) } @$gpus]
>>> $kv->push(3, $b)
>>> $kv->pull(3, out=>$a)
>>> print $a->aspdl
[[ 4. 4. 4.]
[ 4. 4. 4.]]
>>> # push a list of keys.
>>> # single device
>>> $kv->push($keys, [map { mx->nd->ones($shape) } 0..@$keys-1)
>>> $b = [map { mx->nd->zeros(shape) } 0..@$keys-1]
>>> $kv->pull($keys, out=>$b)
>>> print $b->[1]->aspdl
[[ 1. 1. 1.]
[ 1. 1. 1.]]
>>> # multiple devices:
>>> $b = [map { [map { mx->nd->ones($shape, ctx => $_) } @$gpus] } @$keys-1]
>>> $kv->push($keys, $b)
>>> $kv->pull($keys, out=>$b)
>>> print $b->[1][1]->aspdl()
[[ 4. 4. 4.]
[ 4. 4. 4.]]
pull
Pull a single value or a sequence of values from the store.
Data consistency:
1. this function returns after adding an operator to the engine. But any
further read on out will be blocked until it is finished.
2. pull is always called after all previous push and pull on the same
key are finished.
3. It pulls the newest value from the store.
Parameters
----------
key : int or array ref of int
Keys
out: NDArray or array ref of NDArray or array ref of array refs of NDArray
According values
priority : int, optional
The priority of the push operation.
The higher the priority, the faster this action is likely
to be executed before other push actions.
Examples
--------
>>> # pull a single key-value pair
>>> $a = mx->nd->zeros($shape)
>>> $kv->pull(3, out=>$a)
>>> print $a->aspdl
[[ 2. 2. 2.]
[ 2. 2. 2.]]
>>> # pull into multiple devices
>>> $b = [map { mx->nd->ones($shape, $_) } @$gpus]
>>> $kv->pull(3, out=>$b)
>>> print $b->[1]->aspdl()
[[ 2. 2. 2.]
[ 2. 2. 2.]]
>>> # pull a list of key-value pairs.
>>> # On single device
>>> $keys = [5, 7, 9]
>>> $b = [map { mx->nd->zeros($shape) } 0..@$keys-1]
>>> $kv->pull($keys, out=>$b)
>>> print $b->[1]->aspdl()
[[ 2. 2. 2.]
[ 2. 2. 2.]]
>>> # On multiple devices
>>> $b = [map { [map { mx->nd->ones($shape, ctx => $_) } @$gpus ] } 0..@$keys-1]
>>> $kv->pull($keys, out=>$b)
>>> print $b->[1][1]->aspdl()
[[ 2. 2. 2.]
[ 2. 2. 2.]]
set_optimizer
Register an optimizer to the store
If there are multiple machines, this process (should be a worker node)
will pack this optimizer and send it to all servers. It returns after
this action is done.
Parameters
----------
optimizer : Optimizer
the optimizer
type
Get the type of this kvstore
Returns
-------
type : str
the string type
rank
Get the rank of this worker node
Returns
-------
rank : int
The rank of this node, which is in [0, get_num_workers())
num_workers
Get the number of worker nodes
Returns
-------
size :int
The number of worker nodes
save_optimizer_states
Save optimizer (updater) state to file
Parameters
----------
fname : str
Path to output states file.
load_optimizer_states
Load optimizer (updater) state from file.
Parameters
----------
fname : str
Path to input states file.
_set_updater
Set a push updater into the store.
This function only changes the local store. Use set_optimizer for
multi-machines.
Parameters
----------
updater : function
the updater function
Examples
--------
>>> my $update = sub { my ($key, input, stored) = @_;
... print "update on key: $key\n";
... $stored += $input * 2; };
>>> $kv->_set_updater($update)
>>> $kv->pull(3, out=>$a)
>>> print $a->aspdl()
[[ 4. 4. 4.]
[ 4. 4. 4.]]
>>> $kv->push(3, mx->nd->ones($shape))
update on key: 3
>>> $kv->pull(3, out=>$a)
>>> print $a->aspdl()
[[ 6. 6. 6.]
[ 6. 6. 6.]]
_barrier
Global barrier between all worker nodes.
For example, assume there are n machines, we want to let machine 0 first
init the values, and then pull the inited value to all machines. Before
pulling, we can place a barrier to guarantee that the initialization is
finished.
_send_command_to_servers
Send a command to all server nodes
Send a command to all server nodes, which will make each server node run
KVStoreServer.controller
This function returns after the command has been executed in all server
nodes.
Parameters
----------
head : int
the head of the command
body : str
the body of the command
create
Create a new KVStore.
Parameters
----------
name : {'local'}
The type of KVStore
- local works for multiple devices on a single machine (single process)
- dist works for multi-machines (multiple processes)
Returns
-------
kv : KVStore
The created AI::MXNet::KVStore