# Module cartridge.twophase

Clusterwide configuration propagation two-phase algorithm.

(Added in v1.2.0-19)

## Functions

### twophase_commit (opts)

Execute the two-phase commit algorithm.

- (upload) If `opts.upload_data` isn’t `nil` , spread it across the servers from `opts.uri_list` .

- (prepare) Run the `opts.fn_prepare` function.

- (commit) If all the servers do `return true` , call `opts.fn_commit` on every server.

- (abort) Otherwise, if at least one server does `return nil, err` or throws an exception, call `opts.fn_abort` on servers which were prepared successfully.

Parameters:

- opts:

  - uri_list: ({string,…}) array of URIs for performing twophase commit

  - upload_data: any Lua object to be uploaded

  - activity_name: (optional string) understandable name of activity used for logging(default: “twophase_commit”)

  - fn_prepare: (string)

  - fn_commit: (string)

  - fn_abort: (string)

Returns:

(boolean) true

Or

(nil)

(table) Error description

### Usage:

    local my_2pc_data = nil

    function _G.my_2pc_prepare(upload_id)
        local data = upload.inbox[upload_id]
        upload.inbox[upload_id] = nil
        if my_2pc_data ~= nil then
            error('Two-phase commit is locked')
        end
        my_2pc_data = data
    end

    function _G.my_2pc_commit()
        -- Apply my_2pc_data
        ...
    end

    function _G.my_2pc_abort()
        twophase_data = nil
    end

    require('cartridge.twophase').twophase_commit({
        uri_list = {...},
        upload_data = ...,
        activity_name = 'my_2pc',
        fn_prepare = '_G.my_2pc_prepare',
        fn_commit = '_G.my_2pc_commit',
        fn_abort = '_G.my_2pc_abort',
    })

### patch_clusterwide (patch)

Edit the clusterwide configuration. Top-level keys are merged with the current configuration. To remove a top-level section, use `patch_clusterwide{key = box.NULL}` .

The function executes following steps:

1. Patches the current configuration.

2. Validates topology on the current server.

III. Executes two-phase commit on all servers in the cluster excluding expelled and disabled ones.

Parameters:

- patch: (table)

Returns:

(boolean) true

Or

(nil)

(table) Error description

### force_reapply (uuids)

Forcefully apply config to the given instances.

In particular:

- Abort two-phase commit (remove `config.prepare` lock)

- Upload the active config from the current instance.

- Apply it (reconfigure all roles)

(Added in v2.3.0-68)

Parameters:

- uuids: ({string,…})

Returns:

(boolean) true

Or

(nil)

(table) Error description

### get_schema ()

Get clusterwide DDL schema.

(Added in v1.2.0-28)

Returns:

(string) Schema in YAML format

Or

(nil)

(table) Error description

### set_schema (schema)

Apply clusterwide DDL schema.

(Added in v1.2.0-28)

Parameters:

- schema: (string) in YAML format

Returns:

(string) The same new schema

Or

(nil)

(table) Error description

### on_patch (trigger_new, trigger_old)

Set up trigger for for patch_clusterwide.

It will be executed before new new config applied.

If the parameters are `(nil, old_trigger)` , then the old trigger is deleted.

The trigger function is called with two argument: - `conf_new` ( `ClusterwideConfig` ) - `conf_old` ( `ClusterWideConfig` )

It is allowed to modify `conf_new` , but not `conf_old` . Return values are ignored. If calling a trigger raises an error, `patch_clusterwide` returns it as `nil, err` .

(Added in v2.1.0-4)

Parameters:

- trigger_new: (function)

- trigger_old: (function)

### Usage:

    local function inject_data(conf_new, _)
        local data_yml = yaml.encode({foo = 'bar'})
        conf_new:set_plaintext('data.yml', data_yml)
    end)

    twophase.on_patch(inject_data) -- set custom patch modifier trigger
    twophase.on_patch(nil, inject_data) -- drop trigger

## Local Functions

### prepare_2pc (upload_id)

Two-phase commit - preparation stage.

Validate the configuration and acquire a lock setting local variable and writing “config.prepare.yml” file. If the validation fails, the lock isn’t acquired and doesn’t have to be aborted.

Parameters:

- upload_id: (string)

Returns:

(boolean) true

Or

(nil)

(table) Error description

### commit_2pc ()

Two-phase commit - commit stage.

Back up the active configuration, commit changes to filesystem by renaming prepared file, release the lock, and configure roles. If any errors occur, configuration is not rolled back automatically. Any problem encountered during this call has to be solved manually.

Returns:

(boolean) true

Or

(nil)

(table) Error description

### abort_2pc ()

Two-phase commit - abort stage.

Release the lock for further commit attempts.

Returns:

(boolean) true