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sql.go
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sql.go
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package sql_exporter
import (
"context"
"database/sql"
"fmt"
"strings"
_ "github.com/ClickHouse/clickhouse-go" // register the ClickHouse driver
_ "github.com/denisenkom/go-mssqldb" // register the MS-SQL driver
_ "github.com/go-sql-driver/mysql" // register the MySQL driver
log "github.com/golang/glog"
_ "github.com/lib/pq" // register the PostgreSQL driver
)
// OpenConnection extracts the driver name from the DSN (expected as the URI scheme), adjusts it where necessary (e.g.
// some driver supported DSN formats don't include a scheme), opens a DB handle ensuring early termination if the
// context is closed (this is actually prevented by `database/sql` implementation), sets connection limits and returns
// the handle.
//
// Below is the list of supported databases (with built in drivers) and their DSN formats. Unfortunately there is no
// dynamic way of loading a third party driver library (as e.g. with Java classpaths), so any driver additions require
// a binary rebuild.
//
// MySQL
//
// Using the https://github.com/go-sql-driver/mysql driver, DSN format (passed to the driver stripped of the `mysql://`
// prefix):
// mysql://username:password@protocol(host:port)/dbname?param=value
//
// PostgreSQL
//
// Using the https://godoc.org/github.com/lib/pq driver, DSN format (passed through to the driver unchanged):
// postgres://username:password@host:port/dbname?param=value
//
// MS SQL Server
//
// Using the https://github.com/denisenkom/go-mssqldb driver, DSN format (passed through to the driver unchanged):
// sqlserver://username:password@host:port/instance?param=value
//
// Clickhouse
//
// Using the https://github.com/kshvakov/clickhouse driver, DSN format (passed to the driver with the`clickhouse://`
// prefix replaced with `tcp://`):
// clickhouse://host:port?username=username&password=password&database=dbname¶m=value
func OpenConnection(ctx context.Context, logContext, dsn string, maxConns, maxIdleConns int) (*sql.DB, error) {
// Extract driver name from DSN.
idx := strings.Index(dsn, "://")
if idx == -1 {
return nil, fmt.Errorf("missing driver in data source name. Expected format `<driver>://<dsn>`.")
}
driver := dsn[:idx]
// Adjust DSN, where necessary.
switch driver {
case "mysql":
dsn = strings.TrimPrefix(dsn, "mysql://")
case "clickhouse":
dsn = "tcp://" + strings.TrimPrefix(dsn, "clickhouse://")
}
// Open the DB handle in a separate goroutine so we can terminate early if the context closes.
var (
conn *sql.DB
err error
ch = make(chan error)
)
go func() {
conn, err = sql.Open(driver, dsn)
close(ch)
}()
select {
case <-ctx.Done():
return nil, ctx.Err()
case <-ch:
if err != nil {
return nil, err
}
}
conn.SetMaxIdleConns(maxIdleConns)
conn.SetMaxOpenConns(maxConns)
if log.V(1) {
if len(logContext) > 0 {
logContext = fmt.Sprintf("[%s] ", logContext)
}
log.Infof("%sDatabase handle successfully opened with driver %s.", logContext, driver)
}
return conn, nil
}
// PingDB is a wrapper around sql.DB.PingContext() that terminates as soon as the context is closed.
//
// sql.DB does not actually pass along the context to the driver when opening a connection (which always happens if the
// database is down) and the driver uses an arbitrary timeout which may well be longer than ours. So we run the ping
// call in a goroutine and terminate immediately if the context is closed.
func PingDB(ctx context.Context, conn *sql.DB) error {
ch := make(chan error, 1)
go func() {
ch <- conn.PingContext(ctx)
close(ch)
}()
select {
case <-ctx.Done():
return ctx.Err()
case err := <-ch:
return err
}
}