A MongoDB compatible embeddable database and toolkit for Go.
A MongoDB compatible embeddable database and toolkit for Go.
To get started, install the package using the go tool:
$ go get -u github.com/256dpi/lungo
This example
shows a basic usage of the mongo compatible API.
The document-oriented database MongoDB has become a widely used data store for
many applications developed with the Go programming language. Both, the deprecatedmgo and the official mongo driver offer a sophisticated interface to connect
to a deployment and ingest and extract data using various commands. While this
is enough for most projects, there are situations in which one thinks: “It would
be cool if I could just do that in memory without asking the server.”
Lungo tries to address this need by re-implementing the data handling mechanics
in Go to be used on the client-side. This allows developers to pre- or
post-process data in the application relieving the server. For example,
applications may utilize this functionality to cache documents and query them
quickly in memory.
But we do not need to stop there. Many developers coming from the SQL ecosystem
enjoy working with SQLite as a simple alternative to bigger SQL databases. It
allows running tests without setting up a database or even small production
apps that write their data to a single backed-up file.
Lungo wants to offer a similar experience by implementing a full MongoDB
compatible embeddable database that persists data in a single file. The
project aims to provide drop-in compatibility with the API exported by the
official Go driver. This way, applications may use lungo for running their
tests or even low-write production deployments without big code changes.
However, one thing this project does not try to do is build another
distributed database. MongoDB itself does a pretty good job at that already.
The codebase is divided into the packages bsonkit, mongokit, dbkit and
the main lungo package.
The bsonkit package provides building blocks that extend the ones found in
the official bson package for handling BSON data. Its functions are mainly
useful to applications that need to inspect, compare, convert, transform,
clone, access, and manipulate BSON data directly in memory.
On top of that, the mongokit package provides the MongoDB data handling
algorithms and structures. Specifically, it implements the MongoDB querying,
update, and sort algorithms as well as a btree based index for documents. All of
that is then bundled as a basic in-memory collection of documents that offers a
familiar CRUD interface.
The dbkit package provides database-centric utilities e.g. atomic file write.
Finally, the lungo package implements the embeddable database and themongo compatible driver. The heavy work is done by the engine and transaction
types that manage access to the basic mongokit.Collection instances. While both
can be used standalone, most users want to use the generic driver interface that
can be used with MongoDB deployments and lungo engines.
On a high level, lungo provides the following features (unchecked features are
planned to be implemented):
While the goal is to implement all MongoDB features in a compatible way, the
architectural difference has implications on some features. Furthermore,
the goal is to build an open and accessible codebase that favors simplicity.
Check out the following sections for details on the implementation.
The driver supports all standard CRUD, index management and namespace management
methods that are also exposed by the official driver. However, to this date, the
driver does not yet support any of the MongoDB commands that can be issued using
the Database.RunCommand method. Most unexported commands are related to query
planning, replication, sharding, and user and role management features that we
do not plan to support. However, we eventually will support some
administrative and diagnostics commands e.g. renameCollection and explain.
Leveraging the mongokit.Match function, lungo supports the following query
operators:
$and, $or, $nor, ($not)$eq, $gt, $lt, $gte, $lte, $ne$in), ($nin), $exist, $type$jsonSchema, $all, $size, $elemMatchAnd the mongokit.Apply function currently supports the following update
operators:
$set, $setOnInsert, $unset, $rename$inc, $mul, $max, $min, ($push)$pop, $currentDate, $[], $[<identifier>]Finally, the mongokit.Project function currently supports the following
projection operators:
$sliceOperators in braces are only partially supported, see comments in code.
The mongokit.Index type supports single field and compound indexes that
optionally enforce uniqueness or index a subset of documents using a partial
filter expression. Single field indexes also support the automated expiry of
documents aka. TTL indexes.
The more advanced multikey, geospatial, text, and hashed indexes are not yet
supported and may be added later, while the deprecated sparse indexes will not.
The recently introduced collation feature, as well as wildcard indexes, are also
subject to future development.
Indexes are currently only used to ensure uniqueness constraints and do not
support filtering and sorting. This will be added in the future together with
support for the explain command to debug the generated query plan.
Lungo supports multi-document transactions using a basic copy on write mechanism.
Every transaction will make a copy of the catalog and clone namespaces before
applying changes. After the new catalog has been written to disk, the transaction
is considered successful and the catalog replaced. Read-only transactions are
allowed to run in parallel as they only serve as snapshots. But write
transactions are run sequentially. We assume write transactions to be fast and
therefore try to prevent abortions due to conflicts (pessimistic concurrency
control). The chosen approach might be changed in the future.
Similar to MongoDB, every CRUD change is also logged to the local.oplog
collection in the same format as consumed by change streams in MongoDB. Based on
that, change streams can be used in the same way as with MongoDB replica sets.
The lungo.Store interface enables custom adapters that store the catalog to
various mediums. The built-in MemoryStore keeps all data in memory while theFileStore writes all data atomically to a single BSON file. The interface may
get more sophisticated in the future to allow more efficient storing methods.
The lungo.Bucket, lungo.UploadStream and lungo.DownloadStream provide a
GridFS implementation similar to the one found in the gridfs package of the
official Go driver. However, some improvements have been made while
re-implementing the package:
context.Context parameter in all lungo.Bucketlungo.DowloadStream implements the io.Seeker interface for convenientThe MIT License (MIT)
Copyright (c) 2019 Joël Gähwiler