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1.16. Module net.box

1.16. Module net.box

The net.box module contains connectors to remote database systems. One variant, to be discussed later, is connecting to MySQL or MariaDB or PostgreSQL (see SQL DBMS modules reference). The other variant, which is discussed in this section, is connecting to Tarantool servers via a network using the built-in net.box module.

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 a remote box,
  • 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, it’s 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. There are, however, cases when a single connection is not enough — for example, when it’s necessary to prioritize requests or to use different authentication IDs.

The diagram below shows possible connection states and transitions:

net_states.svg

On this diagram:

  • The state machine starts in the ‘initial’ state.
  • net_box.connect() method changes the state to ‘connecting’ and spawns a worker fiber.
  • If authentication and schema upload are required, it’s possible later on to re-enter the ‘fetch_schema’ state from ‘active’ if a request fails due to a schema version mismatch error, so schema reload is triggered.
  • conn.close() method sets the state to ‘closed’ and kills the worker. If the transport is already in the ‘error’ state, close() does nothing.
net_box.connect(URI[, {option[s]}])
net_box.new(URI[, {option[s]}])

Note

The names connect() and new() are synonymous with the only difference that connect() is the preferred name, while new() is retained for backward compatibility.

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.

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 database state may have changed by the time it regains control.

Possible options:

  • wait_connected: by default, connection creation is blocked until the connection is established, but passing wait_connected=false makes it return immediately. Also, passing a timeout makes it wait before returning (e.g. wait_connected=1.5 makes it wait at most 1.5 secs).

    Note

    In the presence of reconnect_after, wait_connected ignores transient failures. The wait completes once the connection is established or is closed explicitly.

  • reconnect_after: a net.box instance automatically reconnects any time the connection is broken or if a connection attempt fails. This makes transient network failures become transparent to the application. Reconnect happens automatically in the background, so queries/requests that suffered due to connectivity loss are transparently retried. The number of retries is unlimited, connection attempts are done over the specified timeout (e.g. reconnect_after=5 for 5 secs). Once a connection is explicitly closed (or garbage-collected), reconnects stop.

  • call_16: [since 1.7.2] by default, net.box connections comply with a new binary protocol command for CALL, which is not backward compatible with previous versions. The new CALL 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 be removed in the next major release. All programming language drivers will be gradually changed to use the new CALL. To connect to a Tarantool instance that uses the old CALL, specify call_16=true.

  • console: depending on the option’s value, the connection supports different methods (as if instances of different classes were returned). With console = true, you can use conn methods close(), is_connected(), wait_state(), eval() (in this case, both binary and Lua console network protocols are supported). With console = false (default), you can also use conn database methods (in this case, only the binary protocol is supported).

Parameters:
  • URI (string) – the URI of the target for the connection
  • options – possible options are wait_connected, reconnect_after, call_16 and console
Return:

conn object

Rtype:

userdata

Example:

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})
object conn
conn:ping()

Execute a PING command.

Return:true on success, false on error
Rtype:boolean

Example:

net_box.self:ping()
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

Example:

-- 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 garbage collected 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, ...}

conn.space.space-name:select{...} is the remote-call equivalent of the local call box.space.space-name:select{...}.

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, ...}

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

conn.space.<space-name>:insert{field-value, ...}

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

conn.space.<space-name>:replace{field-value, ...}

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

conn.space.<space-name>:update{field-value, ...}

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

conn.space.<space-name>:upsert{field-value, ...}

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

conn.space.<space-name>:delete{field-value, ...}

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

conn:call(function-name[, arguments])

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.

Example:

conn:call('function5')
conn:eval(Lua-string)

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').

Example:

conn:eval('return 5+5')
conn:timeout(timeout)

timeout(...) is a wrapper which sets a timeout for the request that follows it.

Example:

conn:timeout(0.5).space.tester:update({1}, {{'=', 2, 15}})

All remote calls support execution timeouts. Using a wrapper object makes the remote connection API compatible with the local one, removing the need for a separate timeout argument, which the local version would ignore. Once a request is sent, it cannot be revoked from the remote server even if a timeout expires: the timeout expiration only aborts the wait for the remote server response, not the request itself.

1.16.1. Example

This example shows the use of most of the net.box methods.

The sandbox configuration for this example assumes that:

  • the Tarantool server is running on localhost 127.0.0.1:3301,
  • there is a space named tester with a numeric primary key and with a tuple that contains a key value = 800,
  • the current user has read, write and execute privileges.

Here are commands for a quick sandbox setup:

box.cfg{listen = 3301}
s = box.schema.space.create('tester')
s:create_index('primary', {type = 'hash', parts = {1, 'unsigned'}})
t = s:insert({800, 'TEST'})
box.schema.user.grant('guest', 'read,write,execute', 'universe')

And here starts the example:

tarantool> net_box = require('net.box')
---
...
tarantool> function example()
         >   local conn, wtuple
         >   if net_box.self:ping() then
         >     table.insert(ta, 'self:ping() succeeded')
         >     table.insert(ta, '  (no surprise -- self connection is pre-established)')
         >   end
         >   if box.cfg.listen == '3301' then
         >     table.insert(ta,'The local server listen address = 3301')
         >   else
         >     table.insert(ta, 'The local server listen address is not 3301')
         >     table.insert(ta, '(  (maybe box.cfg{...listen="3301"...} was not stated)')
         >     table.insert(ta, '(  (so connect will fail)')
         >   end
         >   conn = net_box.connect('127.0.0.1:3301')
         >   conn.space.tester:delete{800}
         >   table.insert(ta, 'conn delete done on tester.')
         >   conn.space.tester:insert{800, 'data'}
         >   table.insert(ta, 'conn insert done on tester, index 0')
         >   table.insert(ta, '  primary key value = 800.')
         >   wtuple = conn.space.tester:select{800}
         >   table.insert(ta, 'conn select done on tester, index 0')
         >   table.insert(ta, '  number of fields = ' .. #wtuple)
         >   conn.space.tester:delete{800}
         >   table.insert(ta, 'conn delete done on tester')
         >   conn.space.tester:replace{800, 'New data', 'Extra data'}
         >   table.insert(ta, 'conn:replace done on tester')
         >   conn:timeout(0.5).space.tester:update({800}, {{'=', 2, 'Fld#1'}})
         >   table.insert(ta, 'conn update done on tester')
         >   conn:close()
         >   table.insert(ta, 'conn close done')
         > end
---
...
tarantool> ta = {}
---
...
tarantool> example()
---
...
tarantool> ta
---
- - self:ping() succeeded
  - '  (no surprise -- self connection is pre-established)'
  - The local server listen address = 3301
  - conn delete done on tester.
  - conn insert done on tester, index 0
  - '  primary key value = 800.'
  - conn select done on tester, index 0
  - '  number of fields = 1'
  - conn delete done on tester
  - conn:replace done on tester
  - conn update done on tester
  - conn close done
...