Merge pull request #150 from tsenart/atomic-migrations-table-creation

postgres: Make `ensureVersionTable` atomic

Author: dhui

Gopkg.lock

@@ -104,3 +104,7 @@
 [[constraint]]
   name = "github.com/dhui/dktest"
   version = "0.3.0"
+
+[[constraint]]
+  name = "github.com/hashicorp/go-multierror"
+  version = "1.0.0"

Gopkg.toml

@@ -14,6 +14,7 @@ import (
 
 	"github.com/golang-migrate/migrate/v4"
 	"github.com/golang-migrate/migrate/v4/database"
+	multierror "github.com/hashicorp/go-multierror"
 	"github.com/lib/pq"
 )
 
@@ -332,21 +333,25 @@ func (p *Postgres) Drop() error {
 	return nil
 }
 
-func (p *Postgres) ensureVersionTable() error {
-	// check if migration table exists
-	var count int
-	query := `SELECT COUNT(1) FROM information_schema.tables WHERE table_name = $1 AND table_schema = (SELECT current_schema()) LIMIT 1`
-	if err := p.conn.QueryRowContext(context.Background(), query, p.config.MigrationsTable).Scan(&count); err != nil {
-		return &database.Error{OrigErr: err, Query: []byte(query)}
-	}
-	if count == 1 {
-		return nil
+func (p *Postgres) ensureVersionTable() (err error) {
+	if err = p.Lock(); err != nil {
+		return err
 	}
 
-	// if not, create the empty migration table
-	query = `CREATE TABLE "` + p.config.MigrationsTable + `" (version bigint not null primary key, dirty boolean not null)`
-	if _, err := p.conn.ExecContext(context.Background(), query); err != nil {
+	defer func() {
+		if e := p.Unlock(); e != nil {
+			if err == nil {
+				err = e
+			} else {
+				err = multierror.Append(err, e)
+			}
+		}
+	}()
+
+	query := `CREATE TABLE IF NOT EXISTS "` + p.config.MigrationsTable + `" (version bigint not null primary key, dirty boolean not null)`
+	if _, err = p.conn.ExecContext(context.Background(), query); err != nil {
 		return &database.Error{OrigErr: err, Query: []byte(query)}
 	}
+
 	return nil
 }

database/postgres/postgres.go

@@ -10,14 +10,11 @@ import (
 	"io"
 	"strconv"
 	"strings"
+	"sync"
 	"testing"
-)
 
-import (
 	"github.com/dhui/dktest"
-)
 
-import (
 	dt "github.com/golang-migrate/migrate/v4/database/testing"
 	"github.com/golang-migrate/migrate/v4/dktesting"
 )
@@ -310,6 +307,44 @@ func TestPostgres_Lock(t *testing.T) {
 	})
 }
 
+func TestWithInstance_Concurrent(t *testing.T) {
+	dktesting.ParallelTest(t, specs, func(t *testing.T, c dktest.ContainerInfo) {
+		ip, port, err := c.FirstPort()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// The number of concurrent processes running WithInstance
+		const concurrency = 30
+
+		// We can instantiate a single database handle because it is
+		// actually a connection pool, and so, each of the below go
+		// routines will have a high probability of using a separate
+		// connection, which is something we want to exercise.
+		db, err := sql.Open("postgres", pgConnectionString(ip, port))
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer db.Close()
+
+		db.SetMaxIdleConns(concurrency)
+		db.SetMaxOpenConns(concurrency)
+
+		var wg sync.WaitGroup
+		defer wg.Wait()
+
+		wg.Add(concurrency)
+		for i := 0; i < concurrency; i++ {
+			go func(i int) {
+				defer wg.Done()
+				_, err := WithInstance(db, &Config{})
+				if err != nil {
+					t.Errorf("process %d error: %s", i, err)
+				}
+			}(i)
+		}
+	})
+}
 func Test_computeLineFromPos(t *testing.T) {
 	testcases := []struct {
 		pos      int

database/postgres/postgres_test.go

@@ -19,6 +19,7 @@ require (
 	github.com/google/go-querystring v1.0.0 // indirect
 	github.com/google/martian v2.1.0+incompatible // indirect
 	github.com/gopherjs/gopherjs v0.0.0-20181004151105-1babbf986f6f // indirect
+	github.com/hashicorp/go-multierror v1.0.0
 	github.com/jackc/fake v0.0.0-20150926172116-812a484cc733 // indirect
 	github.com/jackc/pgx v3.2.0+incompatible // indirect
 	github.com/jmespath/go-jmespath v0.0.0-20180206201540-c2b33e8439af // indirect

go.mod

@@ -100,6 +100,10 @@ github.com/gorilla/mux v1.6.2 h1:Pgr17XVTNXAk3q/r4CpKzC5xBM/qW1uVLV+IhRZpIIk=
 github.com/gorilla/mux v1.6.2/go.mod h1:1lud6UwP+6orDFRuTfBEV8e9/aOM/c4fVVCaMa2zaAs=
 github.com/hailocab/go-hostpool v0.0.0-20160125115350-e80d13ce29ed h1:5upAirOpQc1Q53c0bnx2ufif5kANL7bfZWcc6VJWJd8=
 github.com/hailocab/go-hostpool v0.0.0-20160125115350-e80d13ce29ed/go.mod h1:tMWxXQ9wFIaZeTI9F+hmhFiGpFmhOHzyShyFUhRm0H4=
+github.com/hashicorp/errwrap v1.0.0 h1:hLrqtEDnRye3+sgx6z4qVLNuviH3MR5aQ0ykNJa/UYA=
+github.com/hashicorp/errwrap v1.0.0/go.mod h1:YH+1FKiLXxHSkmPseP+kNlulaMuP3n2brvKWEqk/Jc4=
+github.com/hashicorp/go-multierror v1.0.0 h1:iVjPR7a6H0tWELX5NxNe7bYopibicUzc7uPribsnS6o=
+github.com/hashicorp/go-multierror v1.0.0/go.mod h1:dHtQlpGsu+cZNNAkkCN/P3hoUDHhCYQXV3UM06sGGrk=
 github.com/jackc/fake v0.0.0-20150926172116-812a484cc733 h1:vr3AYkKovP8uR8AvSGGUK1IDqRa5lAAvEkZG1LKaCRc=
 github.com/jackc/fake v0.0.0-20150926172116-812a484cc733/go.mod h1:WrMFNQdiFJ80sQsxDoMokWK1W5TQtxBFNpzWTD84ibQ=
 github.com/jackc/pgx v3.2.0+incompatible h1:0Vihzu20St42/UDsvZGdNE6jak7oi/UOeMzwMPHkgFY=