Support read only source database

Read only database does not expose detailed schema so we have to build it from ground up.

.gitignore

@@ -1,3 +1,4 @@
 .pgsql/data
 bin
 dist/
+*.sql

Makefile

@@ -14,7 +14,7 @@ is-postgres-running:
 
 .PHONY: pgweb
 pgweb:is-postgres-running
-	@pgweb --url "postgres://test_source@localhost:5432/test_source?sslmode=disable"
+	@pgweb --url "postgres://test_target@localhost:5432/test_target?sslmode=disable"
 
 build:
 	rm -rf dist

README.md

@@ -3,7 +3,14 @@
 [![lint](https://github.com/teamniteo/pg-subsetter/actions/workflows/lint.yml/badge.svg)](https://github.com/teamniteo/pg-subsetter/actions/workflows/lint.yml) [![build](https://github.com/teamniteo/pg-subsetter/actions/workflows/go.yml/badge.svg)](https://github.com/teamniteo/pg-subsetter/actions/workflows/go.yml) [![vuln](https://github.com/teamniteo/pg-subsetter/actions/workflows/vuln.yml/badge.svg)](https://github.com/teamniteo/pg-subsetter/actions/workflows/vuln.yml)
 
 
-`pg-subsetter` is a tool designed to synchronize a fraction of a PostgreSQL database to another PostgreSQL database on the fly, it does not copy the SCHEMA. This means that your target database has to have schema populated in some other way.
+`pg-subsetter` is a tool designed to synchronize a fraction of a PostgreSQL database to another PostgreSQL database on the fly, it does not copy the SCHEMA. 
+
+This means that your target database has to have schema populated in some other way. One can for example genrate schema dump with pg_dump:
+
+```bash
+pg_dump --schema-only -n public -f schemadump.sql bigdb
+psql -f schemadump.sql littledb
+```
 
 ### Database Fraction Synchronization
 `pg-subsetter` allows you to select and sync a specific subset of your database. Whether it's a fraction of a table or a particular dataset, you can have it replicated in another database without synchronizing the entire DB.
@@ -17,6 +24,8 @@ Utilizing the native PostgreSQL COPY command, `pg-subsetter` performs data trans
 ### Stateless Operation
 `pg-subsetter` is built to be stateless, meaning it does not maintain any internal state between runs. This ensures that each synchronization process is independent, enhancing reliability and making it easier to manage and scale.
 
+### Sync required rows
+`pg-subsetter` can be isntructed to copy certain rows in specific tables, the command can be used multipel times to sync more data.
 
 ## Usage
 

flake.nix

@@ -3,7 +3,7 @@
     allowed-users = [ "@wheel" "@staff" ]; # allow compiling on every device/machine
   };
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/release-23.05";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
     flake-parts.url = "github:hercules-ci/flake-parts";
   };
   outputs = inputs@{ self, nixpkgs, flake-parts, ... }:

go.mod

@@ -14,6 +14,7 @@ require (
 )
 
 require (
+	github.com/davecgh/go-spew v1.1.1
 	github.com/jackc/pgx/v5 v5.4.3
 	github.com/mattn/go-colorable v0.1.12 // indirect
 	github.com/mattn/go-isatty v0.0.14 // indirect

go.sum

@@ -1,6 +1,7 @@
 github.com/coreos/go-systemd/v22 v22.5.0/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/godbus/dbus/v5 v5.0.4/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
 github.com/jackc/pgpassfile v1.0.0 h1:/6Hmqy13Ss2zCq62VdNG8tM1wchn8zjSGOBJ6icpsIM=
 github.com/jackc/pgpassfile v1.0.0/go.mod h1:CEx0iS5ambNFdcRtxPj5JhEz+xB6uRky5eyVu/W2HEg=

subsetter/query.go

@@ -4,8 +4,10 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"strings"
 
 	"github.com/jackc/pgx/v5/pgxpool"
+	"github.com/samber/lo"
 )
 
 type Table struct {
@@ -14,6 +16,16 @@ type Table struct {
 	Relations []Relation
 }
 
+func (t *Table) RelationNames() (names string) {
+	rel := lo.Map(t.Relations, func(r Relation, _ int) string {
+		return r.ForeignTable + ">" + r.ForeignColumn
+	})
+	if len(rel) > 0 {
+		return strings.Join(rel, ", ")
+	}
+	return "none"
+}
+
 func GetTablesWithRows(conn *pgxpool.Pool) (tables []Table, err error) {
 	q := `SELECT
 		relname,

subsetter/relations.go

@@ -3,8 +3,10 @@ package subsetter
 import (
 	"context"
 	"fmt"
+	"regexp"
 
 	"github.com/jackc/pgx/v5/pgxpool"
+	"github.com/samber/lo"
 )
 
 type Relation struct {
@@ -18,40 +20,57 @@ func (r *Relation) Query() string {
 	return fmt.Sprintf(`SELECT * FROM %s WHERE %s IN (SELECT %s FROM %s)`, r.ForeignTable, r.ForeignColumn, r.PrimaryColumn, r.PrimaryTable)
 }
 
+type RelationInfo struct {
+	TableName    string
+	ForeignTable string
+	SQL          string
+}
+
+func (r *RelationInfo) toRelation() Relation {
+	var rel Relation
+	re := regexp.MustCompile(`FOREIGN KEY \((\w+)\) REFERENCES (\w+)\((\w+)\).*`)
+	matches := re.FindStringSubmatch(r.SQL)
+	if len(matches) == 4 {
+		rel.PrimaryColumn = matches[1]
+		rel.ForeignTable = matches[2]
+		rel.ForeignColumn = matches[3]
+	}
+	rel.PrimaryTable = r.TableName
+	return rel
+}
+
 // GetRelations returns a list of tables that have a foreign key for particular table.
 func GetRelations(table string, conn *pgxpool.Pool) (relations []Relation, err error) {
 
 	q := `SELECT
-		kcu.table_name AS foreign_table_name,
-		kcu.column_name AS foreign_column_name,
-		ccu.table_name,
-		ccu.column_name
+		conrelid::regclass AS table_name,
+		confrelid::regclass AS refrerenced_table,
+		pg_get_constraintdef(c.oid, TRUE) AS sql
 	FROM
-		information_schema.table_constraints tc
-		JOIN information_schema.key_column_usage kcu ON tc.constraint_name = kcu.constraint_name
-			AND tc.table_schema = kcu.table_schema
-		JOIN information_schema.referential_constraints rc ON tc.constraint_name = rc.constraint_name
-			AND tc.table_schema = rc.constraint_schema
-		JOIN information_schema.constraint_column_usage ccu ON rc.unique_constraint_name = ccu.constraint_name
+		pg_constraint c
+		JOIN pg_namespace n ON n.oid = c.connamespace
 	WHERE
-		tc.constraint_type = 'FOREIGN KEY'
-		AND ccu.table_name = $1
-		AND tc.table_schema = 'public';`
+		c.contype = 'f'
+		AND n.nspname = 'public';`
 
-	rows, err := conn.Query(context.Background(), q, table)
+	rows, err := conn.Query(context.Background(), q)
 	if err != nil {
 		return
 	}
 	defer rows.Close()
 
 	for rows.Next() {
-		var rel Relation
-		err = rows.Scan(&rel.ForeignTable, &rel.ForeignColumn, &rel.PrimaryTable, &rel.PrimaryColumn)
+		var rel RelationInfo
+
+		err = rows.Scan(&rel.TableName, &rel.ForeignTable, &rel.SQL)
 		if err != nil {
 			return
 		}
-		relations = append(relations, rel)
+		relations = append(relations, rel.toRelation())
 	}
+	relations = lo.Filter(relations, func(rel Relation, _ int) bool {
+		return rel.PrimaryTable == table
+	})
 
 	return
 }

subsetter/relations_test.go

@@ -4,6 +4,7 @@ import (
 	"reflect"
 	"testing"
 
+	"github.com/davecgh/go-spew/spew"
 	"github.com/jackc/pgx/v5/pgxpool"
 )
 
@@ -44,3 +45,35 @@ func TestRelation_Query(t *testing.T) {
 		})
 	}
 }
+
+func TestRelationInfo_toRelation(t *testing.T) {
+
+	tests := []struct {
+		name   string
+		fields RelationInfo
+		want   Relation
+	}{
+		{
+			"Simple",
+			RelationInfo{"relation", "simple", "FOREIGN KEY (simple_id) REFERENCES simple(id)"},
+			Relation{"relation", "simple_id", "simple", "id"},
+		},
+		{
+			"Simple with cascade",
+			RelationInfo{"relation", "simple", "FOREIGN KEY (simple_id) REFERENCES simple(id) ON DELETE CASCADE"},
+			Relation{"relation", "simple_id", "simple", "id"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			r := &RelationInfo{
+				TableName:    tt.fields.TableName,
+				ForeignTable: tt.fields.ForeignTable,
+				SQL:          tt.fields.SQL,
+			}
+			if got := r.toRelation(); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("RelationInfo.toRelation() = %v, want %v", spew.Sdump(got), spew.Sdump(tt.want))
+			}
+		})
+	}
+}

subsetter/sync.go

@@ -32,7 +32,7 @@ func NewSync(source string, target string, fraction float64, force []Force, verb
 		return nil, err
 	}
 
-	dst, err := pgxpool.New(context.Background(), source)
+	dst, err := pgxpool.New(context.Background(), target)
 	if err != nil {
 		return nil, err
 	}
@@ -60,9 +60,11 @@ func (s *Sync) Close() {
 func copyTableData(table Table, source *pgxpool.Pool, destination *pgxpool.Pool) (err error) {
 	var data string
 	if data, err = CopyTableToString(table.Name, table.Rows, source); err != nil {
+		log.Error().Err(err).Msgf("Error copying table %s", table.Name)
 		return
 	}
 	if err = CopyStringToTable(table.Name, data, destination); err != nil {
+		log.Error().Err(err).Msgf("Error pasting table %s", table.Name)
 		return
 	}
 	return
@@ -74,16 +76,6 @@ func ViableSubset(tables []Table) (subset []Table) {
 	// Filter out tables with no rows
 	subset = lo.Filter(tables, func(table Table, _ int) bool { return table.Rows > 0 })
 
-	// Get all relations
-	relationsR := lo.FlatMap(subset, func(table Table, _ int) []Relation { return table.Relations })
-	relations := lo.Map(relationsR, func(relation Relation, _ int) string { return relation.ForeignTable })
-
-	// Filter out tables that are relations of other tables
-	// they will be copied later
-	subset = lo.Filter(subset, func(table Table, _ int) bool {
-		return !lo.Contains(relations, table.Name)
-	})
-
 	return
 }
 
@@ -140,8 +132,11 @@ func (s *Sync) Sync() (err error) {
 
 	if s.verbose {
 		for _, t := range subset {
-			log.Info().Msgf("Copying table %s with %d rows", t.Name, t.Rows)
-			log.Info().Msgf("Relations: %v", t.Relations)
+			log.Info().
+				Str("table", t.Name).
+				Int("rows", t.Rows).
+				Str("related", t.RelationNames()).
+				Msg("Prepared for sync")
 
 		}
 	}

subsetter/sync_test.go

@@ -1,17 +1,10 @@
 package subsetter
 
 import (
-	"os"
 	"reflect"
 	"testing"
 )
 
-func skipCI(t *testing.T) {
-	if os.Getenv("CI") != "" {
-		t.Skip("Skipping testing in CI environment")
-	}
-}
-
 func TestViableSubset(t *testing.T) {
 	tests := []struct {
 		name       string
@@ -43,7 +36,6 @@ func TestViableSubset(t *testing.T) {
 }
 
 func TestSync_CopyTables(t *testing.T) {
-	skipCI(t)
 	src := getTestConnection()
 	dst := getTestConnectionDst()
 	initSchema(src)