go-dqlite 
This repository provides the go-dqlite Go package, containing bindings for the
dqlite C library and a pure-Go
client for the dqlite wire protocol.
Usage
The best way to understand how to use the go-dqlite package is probably by
looking at the source code of the demo
program and
use it as example.
In general your application will use code such as:
dir := "/path/to/data/directory"
address := "1.2.3.4:666" // Unique node address
cluster := []string{...} // Optional list of existing nodes, when starting a new node
app, err := app.New(dir, app.WithAddress(address), app.WithCluster(cluster))
if err != nil {
// ...
}
db, err := app.Open(context.Background(), "my-database")
if err != nil {
// ...
}
// db is a *sql.DB object
if _, err := db.Exec("CREATE TABLE my_table (n INT)"); err != nil
// ...
}Build
In order to use the go-dqlite package in your application, you'll need to have the dqlite C library installed on your system, along with its dependencies.
By default, go-dqlite's client module supports storing a cache of the
cluster's state in a SQLite database, locally on each cluster member. (This is
not to be confused with any SQLite databases that are managed by dqlite.) In
order to do this, it imports https://github.com/mattn/go-sqlite3, and so you
can use the libsqlite3 build tag to control whether go-sqlite3 links to a
system libsqlite3 or builds its own. You can also disable support for SQLite
node stores entirely with the nosqlite3 build tag (unique to go-dqlite). If
you pass this tag, your application will not link directly to libsqlite3 (but
it will still link it indirectly via libdqlite, unless you've dropped the
sqlite3.c amalgamation into the dqlite build).
Documentation
The documentation for this package can be found on pkg.go.dev.
Demo
To see dqlite in action, either install the Debian package from the PPA:
sudo add-apt-repository -y ppa:dqlite/dev
sudo apt install dqlite-tools libdqlite-devor build the dqlite C library and its dependencies from source, as described here, and then run:
go install -tags libsqlite3 ./cmd/dqlite-demo
from the top-level directory of this repository.
This builds a demo dqlite application, which exposes a simple key/value store over an HTTP API.
Once the dqlite-demo binary is installed (normally under ~/go/bin or
/usr/bin/), start three nodes of the demo application:
dqlite-demo --api 127.0.0.1:8001 --db 127.0.0.1:9001 &
dqlite-demo --api 127.0.0.1:8002 --db 127.0.0.1:9002 --join 127.0.0.1:9001 &
dqlite-demo --api 127.0.0.1:8003 --db 127.0.0.1:9003 --join 127.0.0.1:9001 &The --api flag tells the demo program where to expose its HTTP API.
The --db flag tells the demo program to use the given address for internal
database replication.
The --join flag is optional and should be used only for additional nodes after
the first one. It informs them about the existing cluster, so they can
automatically join it.
Now we can start using the cluster. Let's insert a key pair:
curl -X PUT -d my-value http://127.0.0.1:8001/my-keyand then retrieve it from the database:
curl http://127.0.0.1:8001/my-keyCurrently the first node is the leader. If we stop it and then try to query the key again curl will fail, but we can simply change the endpoint to another node and things will work since an automatic failover has taken place:
kill -TERM %1; curl http://127.0.0.1:8002/my-keyShell
A basic SQLite-like dqlite shell is available in the dqlite-tools package or
can be built with:
go install -tags libsqlite3 ./cmd/dqlite
Usage:
dqlite -s <servers> <database> [command] [flags]
Example usage in the case of the dqlite-demo example listed above:
dqlite -s 127.0.0.1:9001 demo
dqlite> SELECT * FROM model;
my-key|my-value
The shell supports normal SQL queries plus the special .cluster and .leader
commands to inspect the cluster members and the current leader.