Compare · 022

Batch and copyfrom: ClickHouse and TimescaleDB

Every file of the ClickHouse and TimescaleDB versions side by side, with the lines that differ marked. 4 parameter or column types differ in Go.

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Configuration

sgl.yamldiffers

ClickHouse
TimescaleDB
1version: 1
1version: 1
2
2
3databases:
3databases:
4  - name: tides
4  - name: tides
5    dialect: clickhouse
5    dialect: postgres
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
11      driver: clickhouse
11      driver: database/sql
12    migrate:
13      dsn: ${env:DATABASE_URL}

Migrations

db/migrations/0001_readings.up.sqldiffers

ClickHouse
TimescaleDB
1CREATE TABLE readings (
1CREATE TABLE readings (
2    station   String,
2    station   TEXT   NOT NULL,
3    minute    UInt16,
3    minute    BIGINT NOT NULL,
4    height_cm UInt16,
4    height_cm BIGINT NOT NULL,
5    note      Nullable(String)
5    note      TEXT,
6) ENGINE = MergeTree() ORDER BY (station, minute);
6    PRIMARY KEY (station, minute)
7);

db/migrations/0001_readings.down.sqlidentical

ClickHouse
TimescaleDB
1DROP TABLE readings;
1DROP TABLE readings;

Queries

RecordReadingsdiffers

ClickHouse · db/queries/readings.sql
TimescaleDB · db/queries/readings.sql
1-- sgl.query(RecordReadings, batch)
1-- sgl.query(RecordReadings, batch)
2INSERT INTO readings (station, minute, height_cm, note)
2INSERT INTO readings (station, minute, height_cm, note) VALUES ($1, $2, $3, $4);
3VALUES ({station:String}, {minute:UInt16}, {height_cm:UInt16}, {note:Nullable(String)});

SummariseReadingsdiffers

ClickHouse · db/queries/readings.sql
TimescaleDB · db/queries/readings.sql
1-- sgl.query(SummariseReadings, many)
1-- sgl.query(SummariseReadings, many)
2SELECT station, count() AS readings, count(note) AS noted
2SELECT station, COUNT(*) AS readings, COUNT(note) AS noted
3FROM readings
3FROM readings
4GROUP BY station
4GROUP BY station
5ORDER BY station;
5ORDER BY station;

CountPartsonly ClickHouse

ClickHouse · db/queries/readings.sql
TimescaleDB · not in this version
1-- sgl.query(CountParts, one)
2SELECT uniqExact(_part) AS parts FROM readings;

What sgl generates

RecordReadingsdiffers

ClickHouse
TimescaleDB
1func (queries *Queries) RecordReadings(ctx context.Context, params []RecordReadingsParams) error
1func (queries *Queries) RecordReadings(ctx context.Context, params []RecordReadingsParams) error
2
2
3type RecordReadingsParams struct {
3type RecordReadingsParams struct {
4	Station  string
4	Station  string
5	Minute   uint16
5	Minute   int64
6	HeightCm uint16
6	HeightCm int64
7	Note     *string
7	Note     *string
8}
8}

SummariseReadingsdiffers

ClickHouse
TimescaleDB
1func (queries *Queries) SummariseReadings(ctx context.Context) ([]SummariseReadingsRow, error)
1func (queries *Queries) SummariseReadings(ctx context.Context) ([]SummariseReadingsRow, error)
2
2
3type SummariseReadingsRow struct {
3type SummariseReadingsRow struct {
4	Station  string `json:"station"`
4	Station  string `json:"station"`
5	Readings uint64 `json:"readings"`
5	Readings int64  `json:"readings"`
6	Noted    uint64 `json:"noted"`
6	Noted    int64  `json:"noted"`
7}
7}

CountPartsonly ClickHouse

ClickHouse
TimescaleDB · not in this version
1func (queries *Queries) CountParts(ctx context.Context) (CountPartsRow, error)
2
3type CountPartsRow struct {
4	Parts uint64 `json:"parts"`
5}

The program

example.godiffers

ClickHouse
TimescaleDB
1package main
1package main
2
2
3import (
3import (
4	"context"
4	"context"
5	"database/sql"
5	"fmt"
6	"fmt"
6	"io"
7	"io"
7
8
8	"seagull.sh/seagull/examples/clickhouse/022_bulk_writes_native/internal/store"
9	"seagull.sh/seagull/examples/postgres/022_bulk_writes/internal/store"
9)
10)
10
11
11const (
12const (
12	// minutesPerDay is how many readings each tide gauge takes in a day.
13	// minutesPerWeek is how many readings each tide gauge takes in a week.
13	minutesPerDay = 24 * 60
14	minutesPerWeek = 7 * 24 * 60
14)
15)
15
16
16// run records a day of readings from two tide gauges in one batch call, shows how many
17// statementCounter is a store.DBTX that counts the statements sent through ExecContext.
17// parts that wrote, and summarises what landed in the table.
18// QueryContext and QueryRowContext come from the embedded *sql.DB.
19type statementCounter struct {
20	*sql.DB
21
22	// statements is how many times ExecContext has been called.
23	statements int
24}
25
26// ExecContext counts the statement, then runs it on the database.
18//
27//
19// A batch query takes a slice of Params, one per row. On the native driver the generated
28// Takes query (string) which is the SQL to run.
20// method calls PrepareBatch, appends every row with batch.Append and sends them with
29// Takes arguments (...any) which are its bind values.
21// batch.Send: one INSERT, its rows sent column by column in blocks, with no bind
22// variables and so no chunking. The {name:Type} placeholders in the VALUES list only name
23// and type the columns; the driver takes the values from Append. copyfrom generates the
24// same code.
25//
30//
26// Each INSERT writes a new part, which ClickHouse merges in the background, so writing
31// Returns sql.Result which is the database's result.
27// rows one at a time leaves many small parts to merge. CountParts reads the _part virtual
32// Returns error when the statement fails.
28// column to show that the whole day landed as one part.
33func (counter *statementCounter) ExecContext(ctx context.Context, query string, arguments ...any) (sql.Result, error) {
34	counter.statements++
35	return counter.DB.ExecContext(ctx, query, arguments...)
36}
37
38// run records a week of readings from two tide gauges in one batch call, shows how many
39// INSERT statements that took, and summarises what landed in the table.
29//
40//
30// Takes connection (store.DBTX) which is a native connection to a migrated database.
41// Takes database (*sql.DB) which is a migrated database.
31// Takes output (io.Writer) which receives the part counts and the summary.
42// Takes output (io.Writer) which receives the statement counts and the summary.
32//
43//
33// Returns error when a query fails.
44// Returns error when a query fails.
34func run(ctx context.Context, connection store.DBTX, output io.Writer) error {
45func run(ctx context.Context, database *sql.DB, output io.Writer) error {
35	queries := store.New(connection)
46	counter := &statementCounter{DB: database}
47	queries := store.New(counter)
36
48
37	// An empty batch returns at once, without preparing an INSERT, so it writes no part.
49	// An empty batch is a no-op: nothing is sent to the database.
38	if err := queries.RecordReadings(ctx, nil); err != nil {
50	if err := queries.RecordReadings(ctx, nil); err != nil {
39		return fmt.Errorf("recording no readings: %w", err)
51		return fmt.Errorf("recording no readings: %w", err)
40	}
52	}
41	if err := printParts(ctx, queries, 0, output); err != nil {
53	fmt.Fprintf(output, "0 readings sent in %d statements\n", counter.statements)
42		return err
43	}
44
54
45	readings := tideReadings("harbour", "pier")
55	readings := tideReadings("harbour", "pier")
56
57	// A batch query takes a slice of Params, one per row. On database/sql the generated
58	// method writes them as multi-row INSERTs, renumbering the placeholders $1, $2 and on,
59	// chunked so that no statement binds more than 65535 variables, the most the PostgreSQL
60	// protocol can carry: four columns a row allows 16383 rows a statement, so a week from
61	// two gauges takes two. copyfrom generates the same code on database/sql; only the pgx
62	// driver uses COPY.
63	//
64	// Each chunk is its own statement, so run the call inside RunInTx (concept 23) when
65	// every row must land or none.
46	if err := queries.RecordReadings(ctx, readings); err != nil {
66	if err := queries.RecordReadings(ctx, readings); err != nil {
47		return fmt.Errorf("recording readings: %w", err)
67		return fmt.Errorf("recording readings: %w", err)
48	}
68	}
49	if err := printParts(ctx, queries, len(readings), output); err != nil {
69	fmt.Fprintf(output, "%d readings sent in %d statements\n", len(readings), counter.statements)
50		return err
51	}
52
70
53	summary, err := queries.SummariseReadings(ctx)
71	summary, err := queries.SummariseReadings(ctx)
54	if err != nil {
72	if err != nil {
55		return fmt.Errorf("summarising readings: %w", err)
73		return fmt.Errorf("summarising readings: %w", err)
56	}
74	}
57	for _, row := range summary {
75	for _, row := range summary {
58		fmt.Fprintf(output, "%-8s %d readings, %d with a note\n", row.Station, row.Readings, row.Noted)
76		fmt.Fprintf(output, "%-8s %d readings, %d with a note\n", row.Station, row.Readings, row.Noted)
59	}
77	}
60	return nil
78	return nil
61}
79}
62
80
63// printParts prints how many parts hold the table's rows.
81// tideReadings makes one reading a minute for a week at each station. The height rises
64//
82// and falls in a simple saw-tooth, and the reading on the hour carries a note.
65// Takes queries (*store.Queries) which runs the query.
66// Takes sent (int) which is how many readings were sent.
67// Takes output (io.Writer) which receives the line.
68//
69// Returns error when the query fails.
70func printParts(ctx context.Context, queries *store.Queries, sent int, output io.Writer) error {
71	parts, err := queries.CountParts(ctx)
72	if err != nil {
73		return fmt.Errorf("counting parts: %w", err)
74	}
75	fmt.Fprintf(output, "%d readings sent, parts holding rows: %d\n", sent, parts.Parts)
76	return nil
77}
78
79// tideReadings makes one reading a minute for a day at each station. The height rises and
80// falls in a simple saw-tooth, and the reading on the hour carries a note.
81//
83//
82// Takes stations (...string) which name the gauges.
84// Takes stations (...string) which name the gauges.
83//
85//
84// Returns []store.RecordReadingsParams which holds every reading, ready for the batch.
86// Returns []store.RecordReadingsParams which holds every reading, ready for the batch.
85func tideReadings(stations ...string) []store.RecordReadingsParams {
87func tideReadings(stations ...string) []store.RecordReadingsParams {
86	readings := make([]store.RecordReadingsParams, 0, len(stations)*minutesPerDay)
88	readings := make([]store.RecordReadingsParams, 0, len(stations)*minutesPerWeek)
87	for _, station := range stations {
89	for _, station := range stations {
88		for minute := range uint16(minutesPerDay) {
90		for minute := range int64(minutesPerWeek) {
89			var note *string
91			var note *string
90			if minute%60 == 0 {
92			if minute%60 == 0 {
91				note = new(fmt.Sprintf("hour %d check", minute/60))
93				note = new(fmt.Sprintf("hour %d check", minute/60))
92			}
94			}
93			readings = append(readings, store.RecordReadingsParams{
95			readings = append(readings, store.RecordReadingsParams{
94				Station:  station,
96				Station:  station,
95				Minute:   minute,
97				Minute:   minute,
96				HeightCm: 200 + minute%360,
98				HeightCm: 200 + minute%360,
97				Note:     note,
99				Note:     note,
98			})
100			})
99		}
101		}
100	}
102	}
101	return readings
103	return readings
102}
104}

Go type differences

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

Query	Field	ClickHouse	TimescaleDB
RecordReadings	parameter `minute`	`uint16`	`int64`
RecordReadings	parameter `height_cm`	`uint16`	`int64`
SummariseReadings	column `readings`	`uint64`	`int64`
SummariseReadings	column `noted`	`uint64`	`int64`