triton-merci-buckets v1.1.0

This repository is part of the Joyent Triton project. See the contribution guidelines -- Triton does not use GitHub PRs -- and general documentation at the main Triton project page.

Introduction

A significant number of Triton projects use the Moray database in order to store data persistently.

Moray uses "buckets" to store collections of related data. In general, before being able to store data in Moray, a Moray consumer needs to:

1. initialize the buckets it intents to use
2. perform data migrations on data that is already stored

For various reasons, those two tasks are not necessarily straightforward.

This module aims at providing, via an interface that is easy to use, a robust implementation of those two tasks that uses the best practices developed over time by the Triton team.

Important design and implementation choices

Buckets creation/update, reindexing and data migrations handled as a unit

Currently, there is no way to perform buckets creation/update, objects reindexing or data migrations in an arbitrary order when using this module. This is by design.

Controlling the order of those operations allows the implementation of this module to determine when some errors are transient or not. For instance, the data migrations step relies on the fact that all records are reindexed before it starts, so that it can treat any InvalidQueryError when using the data_version indexed field as a transient error.

Field used to store "data version" not configurable

Currently, data migrations require the presence of a data_version indexed field. If that field is not present, the buckets initialization process will assert and make the process exit.

Ideally, consumers of this API would be able to pass the name of the field to use for storing the "data version" of records for each bucket.

Data migration of each record is performed synchronously

This is also by design. The first consumer of this module, sdc-vmapi, did not require performing I/O operations when migrating records, and thus the decision was to keep the implementation as simple as possible.

Usage

var moray = require('moray');
var MorayBucketsInitializer = require('moray-buckets').MorayBucketsInitializer;

var bucketsConfig = {
    fooModel: {
        name: 'foo',
        schema: {
            index: {
                foo: { type: 'string' },
                bar: { type: 'string' },
                baz: { type: 'string' },
                another_indexed_property: { type: 'string' },
                /*
                 * This is required to support data migrations. See "Data
                 * migrations section below"
                 */
                data_version: { type: 'number' }
            },
            options: {
                version: 42
            }
        }
    },
    barModel: {
        name: 'bar',
        schema: {
            index: {
                foo: { type: 'string' },
                bar: { type: 'string' },
                baz: { type: 'string' },
                another_indexed_property: { type: 'string' },
                /*
                 * This is required to support data migrations. See "Data
                 * migrations" section below.
                 */
                data_version: { type: 'number' }
            },
            options: {
                version: 43
            }
        }
    }
};

var morayClient = moray.createClient(morayConfig);

/*
 * The path "dataMigrationsPath" should be a directory with the following
 * structure:
 *
 * fooModel/
 *    001-foo-to-bar.js
 * barModel/
 *    001-foo-to-baz.js
 *    002-baz-to-other-indexed-property.js
 */
morayBucketsInitializer = new MorayBucketsInitializer({
    bucketsConfig: bucketsConfig,
    dataMigrationsPath: dataMigrationsPath,
    log: bunyan.createLogger({name: 'moray-buckets-init'}),
    morayClient: morayClient
});

morayBucketsInitializer.on('error', function bucketsInitError(bucketInitErr) {
    /*
     * Called when a non-transient, non-recoverable error occurs.
    */
    console.error('non-transient error, moray buckets initialization aborted');
});

morayBucketsInitializer.on('buckets-setup-done', function onBucketsSetup() {
    /*
     * Called when all buckets passed as "bucketsConfig" have been created
     * successfully, but not * yet reindexed. Data migrations have also not
     * completed.
     */
    console.log('All buckets are now setup!');
    console.log(morayBucketsInitializer.status());
});

morayBucketsInitializer.on('buckets-reindex-done', function onBucketsReindex() {
    /*
     * Called when all buckets passed as "bucketsConfig" have been created _and_
     * reindexed. At this point, it is safe to perform searches that rely on
     * indexed fields.
     */
    console.log('All buckets are now reindexed!');
});

morayBucketsInitializer.on('data-migrations-done', function onDataMigrated() {
    /*
     * Called when all buckets passed as "bucketsConfig" have been created _and_
     * reindexd, _and_ * after all data migrations have completed successfully.
     */
    console.log('All data migrations have completed successfully!');
});

morayBucketsInitializer.on('done', function onDone() {
    /*
     * This is called when all 'buckets-setup-done', 'buckets-reindex-done' and
     * 'data-migrations-done' events have been emitted.
     */
    console.log('All Moray buckets are initialized!');
});

morayClient.on('connect', function onMorayClientConnected() {
    morayBucketsInitializer.start();
});

MorayBucketsInitializer();

API

MorayBucketsInitializer constructor

var morayBuckets = require('moray-buckets').MorayBucketsInitializer;
var bucketsInitializer = new MorayBucketsInitializer(options);

options is an object with the following properties:

Once a MorayBucketsInitializer instance is created, the buckets initialization process does not start automatically. In order to start the initialization process, the start() method needs to be called.

MorayBucketsInitializer.start()

Starts the buckets initialization process. It performs the following steps in sequence:

1. Creates or updates all moray buckets

2. Reindexes all moray buckets

3. If a dataMigrationsPath key is present in the options argument passed to the constructor, it runs all data migrations

Once the start() method is called, the instance on which it was called may emit events. See the "Events" section below for more details.

If called more than once, start() will throw a BucketsInitAlreadyStartedError.

MorayBucketsInitializer.status()

Returns an object that represents the current state of the buckets initialization process. The returned object has the following form:

{
    bucketsSetup: {
        state: 'DONE',
        /*
         * Only present if the buckets creation/update process encountered an error.
         */
        latestError: errorObject
    },
    bucketsReindex: {
        state: 'DONE',
        /*
         * Only present if the reindexing process encountered an error.
         */
        latestError: errorObject
    },
    dataMigrations: {
        state: 'DONE',
        /*
         * Only present if data migrations are specified in the
         * MorayBucketsInitializer constructor. Each key of the "latestErrors"
         * corresponds to a model name as specified in the "bucketsConfig"
         * parameter passed to the MorayBucketsInitializer constructor.
         */
        latestErrors: {
            model_name: someErrorObject
            other_model_name: anotherErrorObject
        }
    }
}

Each state value in the status object above can have the following values:

• NOT_STARTED
• STARTED
• DONE
• ERROR

Events

done

Emitted when all required steps to initialize buckets and migrate data have completed successfully. See below for more granular events (buckets-setup-done, buckets-reindex-done and data-migrations-done).

error

Emitted when a non-transient error was encountered. A non-transient error can be the result of:

• a non-transient error at the Moray server/Moray client layer

• the maximum number of retries being reached by any of the buckets initialization step described above

buckets-setup-done

Emitted when the first step of the buckets initialization process (creating/updating all buckets) has completed successfully. At this point read/write operations on all buckets should succeed, but:

• findObjects requests may fail, as all objects may not be completely reindexed (see the buckets-reindex-done event for that use case)

• data migrations haven't run, so some objects may be outdated

buckets-reindex-done

Emitted when all objects have been reindexed. Due to the way Moray caches buckets schemas, it is still not necessarily safe to perform findObjects requests without using the requireIndexes options, as they may return erroneous results until all bucket caches are refreshed across all Moray instances.

data-migrations-done

Emitted when all data migrations have completed successfully.

Errors

BucketsInitAlreadyStartedError

InvalidDataMigrationFileNamesError

InvalidIndexesRemovalError

SchemaChangesSameVersionError

Data migrations

Data migrations are an optional part of the buckets initialization process. If no dataMigrationsPath field is present in the options object passed to the MorayBucketsInitializer object, no data migration will be performed.

Data migrations currently use a fixed indexed field to record the "data version" for each record in a given bucket. That field is named data_version.

Data versions for all records start at 1, and object that do not have a data_version field are considered to not have any version.

Structure on disk

See the data migrations files in sdc-vmapi for an example.

Example data migration

Each migration that migrates records for a given model from one version to the next must be implemented as a node module that implements the following interface:

• It exports a DATA_VERSION field that identifies what the target version for that migration module is.

• It exports a migrateRecord function function migrateRecord(record) where record is the record to migrate.

The migrateRecord function is called synchronously by this module, and it must return the migrated object. Mutating the record object passed as input is fine.

Here is a simple migration module that handles migrating records from version 0 (i.e records with no version information) to version 1 by setting the field bar of all objects to foo:

var assert = require('assert-plus');

var DATA_VERSION = 1;

module.exports = {
    DATA_VERSION: DATA_VERSION,
    migrateRecord: function migrateRecord(record) {
        assert.object(record, 'record');
        record.value.bar = 'foo';
        record.value.data_version = DATA_VERSION;
        return record;
    }
};

Development

Describe steps necessary for development here.

make all

Test

Describe steps necessary for testing here.

make test

License

"moray-buckets" is licensed under the Mozilla Public License version 2.0. See the file LICENSE.