dbsync

dbsync

dbsync is a schema migration / database change management tool, similar to flyway but less opinionated and more flexible.

At its most basic level, dbsync is a command line tool that scans a path for files to run as SQL migrations. Migrations found which have not been (successfully) run before will be run in ascending order based on path/filename. Various options can be used to change those basic behaviors.

Supported databases

dbsync supports any database that Knex.js does. For now, that means:

• Postgres
• MySQL
• MariaDB
• SQLite3
• and maybe Oracle (mentioned in the Knex docs as experimental support)

The db "migration" concept

Any time a change in the code requires a change in the db structure, a transformation of the data, and/or a small amount of new data to be inserted, it should happen as a SQL "migration".

Generally, once a migration has been applied to a given database, it will not be applied again to that same database.

Migration files are not inspected for changes; if the filename is the same as a previously successful migration, it will not be run again.

A migration file will either be applied in its entirety or not at all. If a migration is not applied (due to an error), no more migrations will be attempted, and the failed migration will be attempted again on next execution.

Migrations are ordered; they are applied in alphabetical order by filename, including path.

Using dbsync to perform migrations

dbsync should be scripted to occur as part of application deploy and/or startup, and so should rarely need to be initiated independently.

Data should almost always be inserted via INSERT statements, usually with column names, e.g. INSERT INTO table_name (col_name_1, col_name_2, ...) VALUES (value1, value2, ...);

Avoid inserting values into columns that can be auto-generated (like serial ids) – let the column's sequence assign the value. If these auto-generated ids need to be used in SQL somewhere else in the migration, it's still best to let the value get auto-generated, and then just select it later.

Command line use

In order to use dbsync as a stand-alone utility, you will need to install the appropriate database node client module (see the Knex.js documentation for supported clients), either locally wherever dbsync will be used, or globally.

Below are the details of command line options available for dbsync (the same help block can be displayed by running dbsync --help).

  --help, -h             Show help                                                                  
  --path, -p             Directory to scan for migration files; this part of the file path will not
                         be used when determining whether a migration has been run before.
                                                                                          [required]
  --client, --db         A db client string, as appropriate to pass to knex in the initialization
                         object: http://knexjs.org/#Installation-client                   [required]
  --connection, --conn   Additional db connection options, as appropriate to pass to knex in the
                         initialization object: http://knexjs.org/#Installation-client  In order to
                         set subproperties, use dot notation as in these examples: 
                         --client=pg --connection=postgres://user:pw@host:port/dbname?options 
                         --client=mysql --connection.user=user --connection.host=localhost 
                         --client=sqlite3 --connection.filename=./mydb.sqlite             [required]
  --table, -t            Table name for tracking migrations           [default: "dbsync_migrations"]
  --files, -f            Glob pattern used to filter which files in the path are treated as
                         migrations.  May be specified multiple times, in which case files matching
                         any of the globs will be treated as migrations.          [default: "*.sql"]
  --encoding, -e         Encoding to use when reading files.                       [default: "utf8"]
  --case-sensitive, -c   If set, the glob pattern will be matched against files as a case-sensitive
                         pattern.                                                                   
  --recursive, -r        If set, subdirectories within the path will be traversed and searched for
                         migrations matching the filter pattern; this option is ignored if the
                         files glob option contains a slash character.                              
  --order, -o            Governs whether migrations are ordered based on the file's basename alone,
                         or the full file path; must be one of: basename, path     [default: "path"]
  --logging, -l          Logging verbosity; must be one of: debug, info, warn, error, silent
                                                                                   [default: "info"]
  --on-read-error        Governs behavior when an unusual directory read error is encountered; must
                         be one of: ignore, log, exit                              [default: "exit"]
  --test                 If set, instead of performing migrations, dbsync will simply log any
                         messages about actions it would have performed normally.                   
  --autocommit           If set, the commands in the migrations will be run and committed
                         individually, rather than wrapping each migration inside a single
                         transaction; this is useful if you want to manually manage multiple
                         transactions within a migration, or if you want to execute commands not
                         allowed within a transaction (like DROP DATABASE).  This option conflicts
                         with --migration-at-once and --one-transaction.                            
  --migration-at-once    If set, dbsync will not count lines or commands, but instead will load
                         each migration entirely into memory and pass it to the db at once.  This
                         will keep dbsync from processing the text of the migration, but might
                         require a lot of memory for large migrations.  This option conflicts with
                         --autocommit.                                                              
  --one-transaction, -1  If set, dbsync will run all the migrations as a single transaction, rather
                         than one transaction per migration.  Migration table initialization, and
                         updates to the migration table for pending and failed migrations will not
                         be executed as part of this transaction.  This option conflicts with
                         --autocommit.                                                              
  --forget               If set, dbsync will not record any migrations that it performs during this
                         run, nor will it create the migrations table if it doesn't yet exist, but
                         it will still refuse to run migrations that have succeeded previously
                         (unless --blindly is also used); this is useful for scripting misc db
                         commands without requiring any additional client tools to be installed.    
  --blindly              If set, dbsync will not restrict the migrations performed to only those
                         that have not run successfully before; this is useful for rerunning
                         previously-run scripts during development, or for scripting misc db
                         commands without requiring any additional client tools to be installed.    
  --dollar-quoting       If set, dbsync will allow dollar-quoted strings as specified by
                         PostgreSQL. This is not relevant when --migration-at-once is also used.
                         For more details, see section 4.1.2.4. (Dollar-quoted String Constants) of
                         http://www.postgresql.org/docs/9.3/static/sql-syntax-lexical.html          
  --command-buffering    This sets the number of SQL commands to buffer before pausing reading from
                         the file; must be a positive integer. This is a performance-tuning option
                         and shouldn't need to be altered for most use cases.           [default: 4]
  --stack-traces         If set, stack traces will be logged with any errors (when present).

Programmatic usage

dbsync may also be used programmatically as a node dependency. All the features available through the command line are still available when used this way, plus some additional flexibility not available from the command line.

This module is written in coffeescript, but may be used via require("dbsync") from either javascript or coffeescript node apps. This module uses promises as implemented by bluebird.

Initialization

require("dbsync") returns the Migrator class; you instantiate a Migrator instance with something like:

var Migrator = require("dbsync");
var migrator = new Migrator(options);

where options is an object containing keys just like the argument options described above, subject to the caveats below:

• The --help command line option has no equivalent in the options object.
• Options required for the command line are also required for the options object, except that path is not required if dbsync will not perform migrations based on files.
• Where multiple forms of an argument option are available for the command line, only the first listed works for programmatic use.
• Options that do not take values will be interpreted as booleans; this is, if the option is given a truthy value, it will be turned on.
• For options that take values, the same allowed values and defaults apply.
• Options allowing dot notation on the command line (such as --connection) correspond a nested object
• Multiple uses of an option (such as --files) correspond to an array of values

Example:

dbsync --client=mysql \
       --conn.user=user \
       --connection.host=localhost \
       --files='*.sql' \
       --files='*.pgsql' \
       --case-sensitive

will use options equivalent to the following options object:

{
  client: 'mysql',
  connection: {
    user: 'user',
    host: 'localhost'
  },
  files: ['*.sql', '*.pgsql'],
  "case-sensitive": true,
  "stack-traces": false   // all booleans default to false, so this is the same as not specifying it
}

Note that invalid options passed to the Migrator constructor could result in thrown errors.

Additional options flexibility

In addition to the options allowed from the command line, the following are also available:

• logging: passing a falsy value is equivalent to 'silent'
• logging: passing an object with functions for its debug, info, warn, and error properties will cause dbsync to use the passed object for logging

Using a Migrator instance

A Migrator instance exposes 4 methods and 1 property of interest:

• migrator.executionContext is an object which may be inspected at any point during or after execution to get information about the execution of the migration set. (This object should never be modified or replaced while a migration set is running.)
• migrator.scanForFiles() returns a promise of an array of strings representing files (relative to the path option) which will be considered for migration, sorted in the order they will be considered according to the order option. Files representing migrations which have already successfully executed will not be filtered from this list.
• migrator.shouldMigrationRun(migrationId) returns a promise of a boolean representing whether the migration needs to run based on the migrator's options (so this function will always yield true when blindly: true is set). The migrationId for a file-based migration is the file's name, including path relative to the path option (as returned by scanForFiles()).
• migrator.doAllMigrationsIfNeeded() is what is used to execute migrations based on a command line invocation. If migrator.executionContext.files is falsy, it will be set with the value returned by migrator.scanForFiles(), then migrator.executionContext.files will be used as its list of migration files. This means it is possible to set a custom list of files (or a custom ordering of files) by setting migrator.executionContext.files before calling migrator.doAllMigrationsIfNeeded(). This method returns a promise which resolves to migrator.executionContext when all the migrations in the list have been skipped (based on the result of migrator.shouldMigrationRun(migrationId)) or have succeeded, or when a single migration fails.
• migrator.doSingleMigrationIfNeeded(migrationId, [migrationSource]) is similar to migrator.doAllMigrationsIfNeeded(), but only performs a single migration (or skips it, based on migrator.shouldMigrationRun(migrationId)), and has a number of advanced behaviors available based on migrationSource:
  • if migrationSource is undefined or null, then migrationId is treated as a filename; otherwise, it migrationId is a user-defined string id which will identify this migration.
  • if migrationSource is a string, the string will be used as the content of the migration.
  • if migrationsSource is an instance of stream.Readable, the data from the stream will be used as the content of the migration. Note that the stream must return strings, not buffers. (If you have a stream returning buffers, you can make it return strings by calling myStream.setEncoding(encoding).)
  • if migrationSource is a promise (or then-able) which resolves to a string or a readable stream, the resolved value will be used as described above.
  • if migrationSource is a function, the function will be called and its return value (which must be a string, readable stream, or promise to one of those) will be used as described above. Note that the function will only be called if migrator.shouldMigrationRun(migrationId) resolved to true for migrationId; this makes it useful for migrations that require some effort/time/resources to set up, such as creating a stream that downloads a file from a server. By putting such setup in a function and passing that as the migrationSource, the download will never be initiated unless dbsync intends to execute the migration.

Multiple Migrator instances may be created and used in parallel. Since migrating a database is conceptually a serial operation, this should (probably) not be used to perform parallel migrations on the same db, but only to perform migrations on multiple dbs in parallel.

Contributing

Contributions to this project are welcome; please create an issue ticket for bugs or feature requests, and submit a PR if you have made improvements. Feature requests submitted without a quality PR may not be implemented quickly.