Module net.box

Overview

The net.box module contains connectors to remote database systems. One variant, to be discussed later, is for connecting to MySQL or MariaDB or PostgreSQL (see SQL DBMS modules reference). The other variant, which is discussed in this section, is for connecting to Tarantool server instances via a network. For a quick start with net.box, refer to the tutorial.

You can call the following methods:

• require('net.box') – to get a net.box object (named net_box for examples in this section)
• net_box.connect() – to connect and get a connection object (named conn for examples in this section)
• other net.box() routines, passing conn:, to execute requests on the remote database system
• conn:close – to disconnect

All net.box methods are fiber-safe, that is, it is safe to share and use the same connection object across multiple concurrent fibers. In fact that is perhaps the best programming practice with Tarantool. When multiple fibers use the same connection, all requests are pipelined through the same network socket, but each fiber gets back a correct response. Reducing the number of active sockets lowers the overhead of system calls and increases the overall server performance. However for some cases a single connection is not enough – for example, when it is necessary to prioritize requests or to use different authentication IDs.

Most net.box methods accept the last {options} argument, which can be:

• {timeout=...}. For example, a method whose last argument is {timeout=1.5} will stop after 1.5 seconds on the local node, although this does not guarantee that execution will stop on the remote server node.
• {buffer=...}. For an example, see the buffer module.
• {is_async=...}. For example, a method whose last argument is {is_async=true} will not wait for the result of a request. See the is_async description.
• {on_push=... on_push_ctx=...}. For receiving out-of-band messages. See the box.session.push() description.
• {return_raw=...} (since version 2.10.0). If set to true, net.box returns response data wrapped in a MsgPack object instead of decoding it to Lua. The default value is false. For an example, see option description below.

The diagram below shows possible connection states and transitions:

On this diagram:

• net_box.connect() method spawns a worker fiber, which will establish the connection and start the state machine.
• The state machine goes to the initial state.
• Authentication and schema upload. It is possible later on to re-enter the fetch_schema state from active to trigger schema reload.
• The state changes to the graceful_shutdown state when the state machine receives a box.shutdown event from the remote host (see conn:on_shutdown()). Once all pending requests are completed, the state machine switches to the error (error_reconnect) state.
• The transport goes to the error state in case of an error. It can happen, for example, if the server closed the connection. If the reconnect_after option is set, instead of the ‘error’ state, the transport goes to the error_reconnect state.
• conn.close() method sets the state to closed and kills the worker. If the transport is already in the error state, close() does nothing.

Index

Below is a list of all net.box functions.

net_box.connect(URI[, {option[s]}])¶

Create a new connection. The connection is established on demand, at the time of the first request. It can be re-established automatically after a disconnect (see reconnect_after option below). The returned conn object supports methods for making remote requests, such as select, update or delete.

Parameters:

URI (string) – the URI of the target for the connection options – the supported options are shown below: user/password: two options to connect to a remote host other than through URI. For example, instead of connect('username:userpassword@localhost:3301') you can write connect('localhost:3301', {user = 'username', password='userpassword'}). wait_connected: a connection timeout. By default, the connection is blocked until the connection is established, but if you specify wait_connected=false, the connection returns immediately. If you specify this timeout, it will wait before returning (wait_connected=1.5 makes it wait at most 1.5 seconds). Note If reconnect_after is greater than zero, then wait_connected ignores transient failures. The wait completes once the connection is established or is closed explicitly. reconnect_after: a number of seconds to wait before reconnecting. The default value, as with the other connect options, is nil. If reconnect_after is greater than zero, then a net.box instance will attempt to reconnect if a connection is lost or a connection attempt fails. This makes transient network failures transparent to the application. Reconnection happens automatically in the background, so requests that initially fail due to connection drops fail, are transparently retried. The number of retries is unlimited, connection retries are made after any specified interval (for example, reconnect_after=5 means that reconnect attempts are made every 5 seconds). When a connection is explicitly closed or when the Lua garbage collector removes it, then reconnect attempts stop. call_16: [since 1.7.2] a new binary protocol command for CALL in net.box connections by default. The new CALL is not backward compatible with previous versions. It no longer restricts a function to returning an array of tuples and allows returning an arbitrary MsgPack/JSON result, including scalars, nil and void (nothing). The old CALL is left intact for backward compatibility. It will not be present in the next major release. All programming language drivers will gradually be switched to the new CALL. To connect to a Tarantool instance that uses the old CALL, specify call_16=true. connect_timeout: a number of seconds to wait before returning “error: Connection timed out”. fetch_schema: a boolean option that controls fetching schema changes from the server. Default: true. If you don’t operate with remote spaces, for example, run only call or eval, set fetch_schema to false to avoid fetching schema changes which is not needed in this case. Important In connections with fetch_schema == false, remote spaces are unavailable and the on_schema_reload triggers don’t work. required_protocol_version: a minimum version of the IPROTO protocol supported by the server. If the version of the IPROTO protocol supported by the server is lower than specified, the connection will fail with an error message. With required_protocol_version = 1, all connections fail where the IPROTO protocol version is lower than 1. required_protocol_features: specified IPROTO protocol features supported by the server. You can specify one or more net.box features from the table below. If the server does not support the specified features, the connection will fail with an error message. With required_protocol_features = {'transactions'}, all connections fail where the server has transactions: false.

net.box feature	Use	IPROTO feature ID	IPROTO versions supporting the feature
streams	Requires streams support on the server	IPROTO_FEATURE_STREAMS	1 and newer
transactions	Requires transactions support on the server	IPROTO_FEATURE_TRANSACTIONS	1 and newer
error_extension	Requires support for MP_ERROR MsgPack extension on the server	IPROTO_FEATURE_ERROR_EXTENSION	2 and newer
watchers	Requires remote watchers support on the server	IPROTO_FEATURE_WATCHERS	3 and newer

To learn more about IPROTO features, see IPROTO_ID and the IPROTO_FEATURES key.

Return:	conn object
Rtype:	userdata

Examples:

net_box = require('net.box')

conn = net_box.connect('localhost:3301')
conn = net_box.connect('127.0.0.1:3302', {wait_connected = false})
conn = net_box.connect('127.0.0.1:3303', {reconnect_after = 5, call_16 = true})
conn = net_box.connect('127.0.0.1:3304', {required_protocol_version = 4, required_protocol_features = {'transactions', 'streams'}, })

net_box.new(URI[, {option[s]}])¶

new() is a synonym for connect(). It is retained for backward compatibility. For more information, see the description of net_box.connect().

object self¶

For a local Tarantool server, there is a pre-created always-established connection object named net_box.self. Its purpose is to make polymorphic use of the net_box API easier. Therefore conn = net_box.connect('localhost:3301') can be replaced by conn = net_box.self.

However, there is an important difference between the embedded connection and a remote one:

• With the embedded connection, requests which do not modify data do not yield. When using a remote connection, due to the implicit rules any request can yield, and the database state may have changed by the time it regains control.
• All the options passed to a request (as is_async, on_push, timeout) will be ignored.

object conn¶

conn:ping([options])¶

Execute a PING command.

Parameters:	options (table) – the supported option is timeout=seconds
Return:	true on success, false on error
Rtype:	boolean

Example:

net_box.self:ping({timeout = 0.5})

conn:wait_connected([timeout])¶

Wait for connection to be active or closed.

Parameters:	timeout (number) – in seconds
Return:	true when connected, false on failure.
Rtype:	boolean

Example:

net_box.self:wait_connected()

conn:is_connected()¶

Show whether connection is active or closed.

Return:	true if connected, false on failure.
Rtype:	boolean

Example:

net_box.self:is_connected()

conn:wait_state(state[s][, timeout])¶

[since 1.7.2] Wait for a target state.

Parameters:	states (string) – target states timeout (number) – in seconds
Return:	true when a target state is reached, false on timeout or connection closure
Rtype:	boolean

Examples:

-- wait infinitely for 'active' state:
conn:wait_state('active')

-- wait for 1.5 secs at most:
conn:wait_state('active', 1.5)

-- wait infinitely for either `active` or `fetch_schema` state:
conn:wait_state({active=true, fetch_schema=true})

conn:close()¶

Close a connection.

Connection objects are destroyed by the Lua garbage collector, just like any other objects in Lua, so an explicit destruction is not mandatory. However, since close() is a system call, it is good programming practice to close a connection explicitly when it is no longer needed, to avoid lengthy stalls of the garbage collector.

Example:

conn:close()

conn.space.<space-name>:select({field-value, ...} [, {options}])

conn.space.space-name:select({...}) is the remote-call equivalent of the local call box.space.space-name:select{...} (see details). For an additional option see Module buffer and skip-header.

Example:

conn.space.testspace:select({1,'B'}, {timeout=1})

Note

Due to the implicit yield rules a local box.space.space-name:select{...} does not yield, but a remote conn.space.space-name:select{...} call does yield, so global variables or database tuples data may change when a remote conn.space.space-name:select{...} occurs.

conn.space.<space-name>:get({field-value, ...} [, {options}])

conn.space.space-name:get(...) is the remote-call equivalent of the local call box.space.space-name:get(...) (see details).

Example:

conn.space.testspace:get({1})

conn.space.<space-name>:insert({field-value, ...} [, {options}])

conn.space.space-name:insert(...) is the remote-call equivalent of the local call box.space.space-name:insert(...) (see details). For an additional option see Module buffer and skip-header.

Example:

conn.space.testspace:insert({2,3,4,5}, {timeout=1.1})

conn.space.<space-name>:replace({field-value, ...} [, {options}])

conn.space.space-name:replace(...) is the remote-call equivalent of the local call box.space.space-name:replace(...) (see details). For an additional option see Module buffer and skip-header.

Example:

conn.space.testspace:replace({5,6,7,8})

conn.space.<space-name>:update({field-value, ...} [, {options}])

conn.space.space-name:update(...) is the remote-call equivalent of the local call box.space.space-name:update(...) (see details). For an additional option see Module buffer and skip-header.

Example:

conn.space.Q:update({1},{{'=',2,5}}, {timeout=0})

conn.space.<space-name>:upsert({field-value, ...} [, {options}])

conn.space.space-name:upsert(...) is the remote-call equivalent of the local call box.space.space-name:upsert(...). (see details). For an additional option see Module buffer and skip-header.

conn.space.<space-name>:delete({field-value, ...} [, {options}])

conn.space.space-name:delete(...) is the remote-call equivalent of the local call box.space.space-name:delete(...) (see details). For an additional option see Module buffer and skip-header.

conn:eval(Lua-string[, {arguments}[, {options}]])¶

conn:eval(Lua-string) evaluates and executes the expression in Lua-string, which may be any statement or series of statements. An execute privilege is required; if the user does not have it, an administrator may grant it with box.schema.user.grant(username, 'execute', 'universe').

To ensure that the return from conn:eval is whatever the Lua expression returns, begin the Lua-string with the word “return”.

Examples:

tarantool> --Lua-string
tarantool> conn:eval('function f5() return 5+5 end; return f5();')
---
- 10
...
tarantool> --Lua-string, {arguments}
tarantool> conn:eval('return ...', {1,2,{3,'x'}})
---
- 1
- 2
- [3, 'x']
...
tarantool> --Lua-string, {arguments}, {options}
tarantool> conn:eval('return {nil,5}', {}, {timeout=0.1})
---
- [null, 5]
...

conn:call(function-name[, {arguments}[, {options}]])¶

conn:call('func', {'1', '2', '3'}) is the remote-call equivalent of func('1', '2', '3'). That is, conn:call is a remote stored-procedure call. The return from conn:call is whatever the function returns.

Limitation: the called function cannot return a function, for example if func2 is defined as function func2 () return func end then conn:call(func2) will return “error: unsupported Lua type ‘function’”.

Examples:

tarantool> -- create 2 functions with conn:eval()
tarantool> conn:eval('function f1() return 5+5 end;')
tarantool> conn:eval('function f2(x,y) return x,y end;')
tarantool> -- call first function with no parameters and no options
tarantool> conn:call('f1')
---
- 10
...
tarantool> -- call second function with two parameters and one option
tarantool> conn:call('f2',{1,'B'},{timeout=99})
---
- 1
- B
...

conn:watch(key, func)¶

Subscribe to events broadcast by a remote host.

Parameters:	key (string) – a key name of an event to subscribe to func (function) – a callback to invoke when the key value is updated
Return:	a watcher handle. The handle consists of one method – unregister(), which unregisters the watcher.

To read more about watchers, see the Functions for watchers section.

The method has the same syntax as the box.watch() function, which is used for subscribing to events locally.

Watchers survive reconnection (see the reconnect_after connection option). All registered watchers are automatically resubscribed when the connection is reestablished.

If a remote host supports watchers, the watchers key will be set in the connection peer_protocol_features. For details, check the net.box features table.

Note

Keep in mind that garbage collection of a watcher handle doesn’t lead to the watcher’s destruction. In this case, the watcher remains registered. It is okay to discard the result of watch function if the watcher will never be unregistered.

Example:

Server:

-- Broadcast value 42 for the 'foo' key.
box.broadcast('foo', 42)

Client:

conn = net.box.connect(URI)
local log = require('log')
-- Subscribe to updates of the 'foo' key.
w = conn:watch('foo', function(key, value)
    assert(key == 'foo')
    log.info("The box.id value is '%d'", value)
end)

If you don’t need the watcher anymore, you can unregister it using the command below:

w:unregister()

conn:request(... {is_async=...})¶

{is_async=true|false} is an option which is applicable for all net_box requests including conn:call, conn:eval, and the conn.space.space-name requests.

The default is is_async=false, meaning requests are synchronous for the fiber. The fiber is blocked, waiting until there is a reply to the request or until timeout expires. Before Tarantool version 1.10, the only way to make asynchronous requests was to put them in separate fibers.

The non-default is is_async=true, meaning requests are asynchronous for the fiber. The request causes a yield but there is no waiting. The immediate return is not the result of the request, instead it is an object that the calling program can use later to get the result of the request.

This immediately-returned object, which we’ll call “future”, has its own methods:

• future:is_ready() which will return true when the result of the request is available,
• future:result() to get the result of the request (returns the response or nil in case it’s not ready yet or there has been an error),
• future:wait_result(timeout) to wait until the result of the request is available and then get it, or throw an error if there is no result after the timeout exceeded,
• future:discard() to abandon the object.

Typically a user would say future=request-name(...{is_async=true}), then either loop checking future:is_ready() until it is true and then say request_result=future:result(), or say request_result=future:wait_result(...). Alternatively the client could check for “out-of-band” messages from the server by calling pairs() in a loop – see box.session.push().

A user would say future:discard() to make a connection forget about the response – if a response for a discarded object is received then it will be ignored, so that the size of the requests table will be reduced and other requests will be faster.

Examples:

-- Insert a tuple asynchronously --
tarantool> future = conn.space.bands:insert({10, 'Queen', 1970}, {is_async=true})
---
...
tarantool> future:is_ready()
---
- true
...
tarantool> future:result()
---
- [10, 'Queen', 1970]
...

-- Iterate through a space with 10 records to get data in chunks of 3 records --
tarantool> while true do
               future = conn.space.bands:select({}, {limit=3, after=position, fetch_pos=true, is_async=true})
               result = future:wait_result()
               tuples = result[1]
               position = result[2]
               if position == nil then
                   break
               end
               print('Chunk size: '..#tuples)
           end
Chunk size: 3
Chunk size: 3
Chunk size: 3
Chunk size: 1
---
...

Typically {is_async=true} is used only if the load is large (more than 100,000 requests per second) and latency is large (more than 1 second), or when it is necessary to send multiple requests in parallel then collect responses (sometimes called a “map-reduce” scenario).

Note

Although the final result of an async request is the same as the result of a sync request, it is structured differently: as a table, instead of as the unpacked values.

conn:request(... {return_raw=...})

{return_raw=true} is ignored for:

• Methods that return nil: begin, commit, rollback, upsert, prepare.
• index.count (returns number).

For execute, the option is applied only to data (rows). Metadata is decoded even if {return_raw=true}.

Example:

local c = require('net.box').connect(uri)
local mp = c.eval('eval ...', {1, 2, 3}, {return_raw = true})
mp:decode() -- {1, 2, 3}

The option can be useful if you want to pass a response through without decoding or with partial decoding. The usage of MsgPack object can reduce pressure on the Lua garbage collector.

conn:new_stream([options])¶

Create a stream.

Example:

-- Start a server to create a new stream
local conn = net_box.connect('localhost:3301')
local conn_space = conn.space.test
local stream = conn:new_stream()
local stream_space = stream.space.test

object stream¶

stream:begin([txn_isolation])¶

Begin a stream transaction. Instead of the direct method, you can also use the call, eval or execute methods with SQL transaction.

Parameters:	txn_isolation – transaction isolation level

stream:commit()¶

Commit a stream transaction. Instead of the direct method, you can also use the call, eval or execute methods with SQL transaction.

Examples:

-- Begin stream transaction
stream:begin()
-- In the previously created ``accounts`` space with the primary key ``test``, modify the fields 2 and 3
stream.space.accounts:update(test_1, {{'-', 2, 370}, {'+', 3, 100}})
-- Commit stream transaction
stream:commit()

stream:rollback()¶

Rollback a stream transaction. Instead of the direct method, you can also use the call, eval or execute methods with SQL transaction.

Example:

-- Test rollback for memtx space
space:replace({1})
-- Select return tuple that was previously inserted, because this select belongs to stream transaction
space:select({})
stream:rollback()
-- Select is empty, stream transaction rollback
space:select({})

Triggers

With the net.box module, you can use the following triggers:

conn:on_connect([trigger-function[, old-trigger-function]])¶

Define a trigger for execution when a new connection is established, and authentication and schema fetch are completed due to an event such as net_box.connect.

If a trigger function issues net_box requests, they must be asynchronous ({is_async = true}). An attempt to wait for request completion with future:pairs() or future:wait_result() in the trigger function will result in an error.

If the trigger execution fails and an exception happens, the connection’s state changes to ‘error’. In this case, the connection is terminated, regardless of the reconnect_after option’s value. Can be called as many times as reconnection happens, if reconnect_after is greater than zero.

Parameters:	trigger-function (function) – the trigger function. Takes the conn object as the first argument. old-trigger-function (function) – an existing trigger function to replace with trigger-function
Return:	nil or function pointer

conn:on_disconnect([trigger-function[, old-trigger-function]])¶

Define a trigger for execution after a connection is closed. If the trigger function causes an error, the error is logged but otherwise is ignored. Execution stops after a connection is explicitly closed, or once the Lua garbage collector removes it.

Parameters:	trigger-function (function) – the trigger function. Takes the conn object as the first argument old-trigger-function (function) – an existing trigger function to replace with trigger-function
Return:	nil or function pointer

conn:on_shutdown([trigger-function[, old-trigger-function]])¶

Define a trigger for shutdown when a box.shutdown event is received.

The trigger starts in a new fiber. While the on_shutdown() trigger is running, the connection stays active. It means that the trigger callback is allowed to send new requests.

After the trigger return, the net.box connection goes to the graceful_shutdown state (check the state diagram for details). In this state, no new requests are allowed. The connection waits for all pending requests to be completed.

Once all in-progress requests have been processed, the connection is closed. The state changes to error or error_reconnect (if the reconnect_after option is defined).

Servers that do not support the box.shutdown event or IPROTO_WATCH just close the connection abruptly. In this case, the on_shutdown() trigger is not executed.

Parameters:	trigger-function (function) – the trigger function. Takes the conn object as the first argument old-trigger-function (function) – an existing trigger function to replace with trigger-function
Return:	nil or function pointer

conn:on_schema_reload([trigger-function[, old-trigger-function]])¶

Define a trigger executed when some operation has been performed on the remote server after schema has been updated. So, if a server request fails due to a schema version mismatch error, schema reload is triggered.

If a trigger function issues net_box requests, they must be asynchronous ({is_async = true}). An attempt to wait for request completion with future:pairs() or future:wait_result() in the trigger function will result in an error.

Parameters:	trigger-function (function) – the trigger function. Takes the conn object as the first argument old-trigger-function (function) – an existing trigger function to replace with trigger-function
Return:	nil or function pointer

Note

If the parameters are (nil, old-trigger-function), then the old trigger is deleted.

If both parameters are omitted, then the response is a list of existing trigger functions.

Find the detailed information about triggers in the triggers section.