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Migrations at start-up: MySQL and ClickHouse

Every file of the MySQL and ClickHouse versions side by side, with the lines that differ marked. 1 parameter or column types differ in Go.

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Configuration

sgl.yamldiffers
MySQL
ClickHouse
1version: 1
1version: 1
2
2
3databases:
3databases:
4 - name: harbour
4 - name: harbour
5 dialect: mysql
5 dialect: clickhouse
6 migrations: db/migrations
6 migrations: db/migrations
7 queries: db/queries
7 queries: db/queries
8 go:
8 go:
9 package: store
9 package: store
10 out: internal/store
10 out: internal/store

Migrations

db/migrations/0001_boats.up.sqldiffers
MySQL
ClickHouse
1CREATE TABLE boats (
1CREATE TABLE boats (
2 id BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
2 id UInt64,
3 name VARCHAR(50) NOT NULL
3 name String
4);
4) ENGINE = MergeTree() ORDER BY id;
db/migrations/0001_boats.down.sqlidentical
MySQL
ClickHouse
1DROP TABLE boats;
1DROP TABLE boats;
db/migrations/0002_boat_home_port.up.sqldiffers
MySQL
ClickHouse
1ALTER TABLE boats ADD COLUMN home_port VARCHAR(50) NOT NULL DEFAULT 'Padstow';
1ALTER TABLE boats ADD COLUMN home_port String DEFAULT 'Padstow';
db/migrations/0002_boat_home_port.down.sqlidentical
MySQL
ClickHouse
1ALTER TABLE boats DROP COLUMN home_port;
1ALTER TABLE boats DROP COLUMN home_port;

Queries

AddBoatdiffers
MySQL · db/queries/boats.sql
ClickHouse · db/queries/boats.sql
1-- sgl.query(AddBoat, exec)
1-- sgl.query(AddBoat, exec)
2INSERT INTO boats (name, home_port) VALUES (?, ?);
2INSERT INTO boats (id, name, home_port) VALUES ({id:UInt64}, {name:String}, {home_port:String});
ListBoatsidentical
MySQL · db/queries/boats.sql
ClickHouse · db/queries/boats.sql
1-- sgl.query(ListBoats, many)
1-- sgl.query(ListBoats, many)
2SELECT id, name, home_port FROM boats ORDER BY id;
2SELECT id, name, home_port FROM boats ORDER BY id;

What sgl generates

AddBoatdiffers
MySQL
ClickHouse
1func (queries *Queries) AddBoat(ctx context.Context, params AddBoatParams) error
1func (queries *Queries) AddBoat(ctx context.Context, params AddBoatParams) error
2
2
3type AddBoatParams struct {
3type AddBoatParams struct {
4 ID uint64
4 Name string
5 Name string
5 HomePort string
6 HomePort string
6}
7}
ListBoatsdiffers
MySQL
ClickHouse
1func (queries *Queries) ListBoats(ctx context.Context) ([]ListBoatsRow, error)
1func (queries *Queries) ListBoats(ctx context.Context) ([]ListBoatsRow, error)
2
2
3type ListBoatsRow struct {
3type ListBoatsRow struct {
4 ID int64 `json:"id"`
4 ID uint64 `json:"id"`
5 Name string `json:"name"`
5 Name string `json:"name"`
6 HomePort string `json:"home_port"`
6 HomePort string `json:"home_port"`
7}
7}

The program

example.godiffers
MySQL
ClickHouse
1package main
1package main
2
2
3import (
3import (
4 "context"
4 "context"
5 "database/sql"
5 "database/sql"
6 "fmt"
6 "fmt"
7 "io"
7 "io"
8 "io/fs"
8 "io/fs"
9
9
10 "seagull.sh/seagull/examples/mysql/027_migrations_at_startup/internal/store"
10 "seagull.sh/seagull/examples/clickhouse/027_migrations_at_startup/internal/store"
11 "seagull.sh/seagull/sdk/migrate"
11 "seagull.sh/seagull/sdk/migrate"
12 "seagull.sh/seagull/sdk/migrate/migrate_backend_mysql"
12 "seagull.sh/seagull/sdk/migrate/migrate_backend_clickhouse"
13)
13)
14
14
15// run starts the program twice against the same database. The first start applies both
15// run starts the program twice against the same database. The first start applies both
16// migrations before the program uses the schema; the second finds nothing to do.
16// migrations before the program uses the schema; the second finds nothing to do.
17//
17//
18// Takes database (*sql.DB) which is the database to migrate, empty or not.
18// Takes database (*sql.DB) which is the database to migrate, empty or not.
19// Takes migrations (fs.FS) which holds db/migrations, the embed.FS in main.go.
19// Takes migrations (fs.FS) which holds db/migrations, the embed.FS in main.go.
20// Takes output (io.Writer) which receives what each start did.
20// Takes output (io.Writer) which receives what each start did.
21//
21//
22// Returns error when migrating or a query fails.
22// Returns error when migrating or a query fails.
23func run(ctx context.Context, database *sql.DB, migrations fs.FS, output io.Writer) error {
23func run(ctx context.Context, database *sql.DB, migrations fs.FS, output io.Writer) error {
24 for _, boat := range []string{"Kittiwake", "Puffin"} {
24 boats := []store.AddBoatParams{
25 {ID: 1, Name: "Kittiwake", HomePort: "Padstow"},
26 {ID: 2, Name: "Puffin", HomePort: "Padstow"},
27 }
28 for _, boat := range boats {
25 if err := start(ctx, database, migrations, boat, output); err != nil {
29 if err := start(ctx, database, migrations, boat, output); err != nil {
26 return err
30 return err
27 }
31 }
28 }
32 }
29 return printHistory(ctx, database, migrations, output)
33 return printHistory(ctx, database, migrations, output)
30}
34}
31
35
32// start is what the program does each time it starts: migrate first, then work. Here the
36// start is what the program does each time it starts: migrate first, then work. Here the
33// work is adding a boat and listing the harbour.
37// work is adding a boat and listing the harbour.
34//
38//
35// Takes database (*sql.DB) which is the database.
39// Takes database (*sql.DB) which is the database.
36// Takes migrations (fs.FS) which holds the migration files.
40// Takes migrations (fs.FS) which holds the migration files.
37// Takes boat (string) which names the boat to add.
41// Takes boat (store.AddBoatParams) which is the boat to add.
38// Takes output (io.Writer) which receives what happened.
42// Takes output (io.Writer) which receives what happened.
39//
43//
40// Returns error when migrating or a query fails.
44// Returns error when migrating or a query fails.
41func start(ctx context.Context, database *sql.DB, migrations fs.FS, boat string, output io.Writer) error {
45func start(ctx context.Context, database *sql.DB, migrations fs.FS, boat store.AddBoatParams, output io.Writer) error {
42 // migrate_backend_mysql.New() is the MySQL backend: it knows how to create the history
46 // migrate_backend_clickhouse.New() is the ClickHouse backend. It runs each statement of
43 // table and holds a GET_LOCK advisory lock, scoped to this schema, while it works, so
47 // a migration without a transaction and records the migration once every statement has
44 // when several copies of a service start at once, one migrates and the rest wait, then
48 // succeeded; it takes no lock, so only one process should migrate at a time. NewMigrator
45 // find nothing to do. MySQL commits each CREATE or ALTER as it runs, so a migration
49 // reads the numbered *.up.sql and *.down.sql files from the directory inside migrations.
46 // cannot be rolled back as a whole: keep each one to a single statement of DDL.
50 migrator, err := migrate.NewMigrator(database, migrate_backend_clickhouse.New(), migrations, "db/migrations")
47 // NewMigrator reads the numbered *.up.sql and *.down.sql files from the directory inside
48 // migrations.
49 migrator, err := migrate.NewMigrator(database, migrate_backend_mysql.New(), migrations, "db/migrations")
50 if err != nil {
51 if err != nil {
51 return err
52 return err
52 }
53 }
53
54
54 // Up applies every migration not yet in the history, in version order, and returns how
55 // Up applies every migration not yet in the history, in version order, and returns how
55 // many it applied. On a database that is up to date it applies none.
56 // many it applied. On a database that is up to date it applies none.
56 applied, err := migrator.Up(ctx)
57 applied, err := migrator.Up(ctx)
57 if err != nil {
58 if err != nil {
58 return fmt.Errorf("migrating: %w", err)
59 return fmt.Errorf("migrating: %w", err)
59 }
60 }
60 fmt.Fprintf(output, "start-up: applied %d migrations\n", applied)
61 fmt.Fprintf(output, "start-up: applied %d migrations\n", applied)
61
62
62 queries := store.New(database)
63 queries := store.New(database)
63 if err := queries.AddBoat(ctx, store.AddBoatParams{Name: boat, HomePort: "Padstow"}); err != nil {
64 if err := queries.AddBoat(ctx, boat); err != nil {
64 return fmt.Errorf("adding %s: %w", boat, err)
65 return fmt.Errorf("adding %s: %w", boat.Name, err)
65 }
66 }
66 boats, err := queries.ListBoats(ctx)
67 listed, err := queries.ListBoats(ctx)
67 if err != nil {
68 if err != nil {
68 return fmt.Errorf("listing boats: %w", err)
69 return fmt.Errorf("listing boats: %w", err)
69 }
70 }
70 for _, row := range boats {
71 for _, row := range listed {
71 fmt.Fprintf(output, " %d %-9s of %s\n", row.ID, row.Name, row.HomePort)
72 fmt.Fprintf(output, " %d %-9s of %s\n", row.ID, row.Name, row.HomePort)
72 }
73 }
73 return nil
74 return nil
74}
75}
75
76
76// printHistory prints the migration history the migrator keeps in the database.
77// printHistory prints the migration history the migrator keeps in the database.
77//
78//
78// Takes database (*sql.DB) which is the migrated database.
79// Takes database (*sql.DB) which is the migrated database.
79// Takes migrations (fs.FS) which holds the migration files.
80// Takes migrations (fs.FS) which holds the migration files.
80// Takes output (io.Writer) which receives the history.
81// Takes output (io.Writer) which receives the history.
81//
82//
82// Returns error when the history cannot be read.
83// Returns error when the history cannot be read.
83func printHistory(ctx context.Context, database *sql.DB, migrations fs.FS, output io.Writer) error {
84func printHistory(ctx context.Context, database *sql.DB, migrations fs.FS, output io.Writer) error {
84 backend := migrate_backend_mysql.New()
85 backend := migrate_backend_clickhouse.New()
85 migrator, err := migrate.NewMigrator(database, backend, migrations, "db/migrations")
86 migrator, err := migrate.NewMigrator(database, backend, migrations, "db/migrations")
86 if err != nil {
87 if err != nil {
87 return err
88 return err
88 }
89 }
89 statuses, err := migrator.Status(ctx)
90 statuses, err := migrator.Status(ctx)
90 if err != nil {
91 if err != nil {
91 return fmt.Errorf("reading migration status: %w", err)
92 return fmt.Errorf("reading migration status: %w", err)
92 }
93 }
93 fmt.Fprintf(output, "history in %s:\n", backend.Names().History)
94 fmt.Fprintf(output, "history in %s:\n", backend.Names().History)
94 for _, status := range statuses {
95 for _, status := range statuses {
95 fmt.Fprintf(output, " %04d %-15s applied=%t\n", status.Version, status.Name, status.Applied)
96 fmt.Fprintf(output, " %04d %-15s applied=%t\n", status.Version, status.Name, status.Applied)
96 }
97 }
97 return nil
98 return nil
98}
99}

Go type differences

The same SQL types map to different Go types, because each database reports them differently.

QueryFieldMySQLClickHouse
ListBoatscolumn idint64uint64