From 98dfce2ae587ebd9b2a2064f457af464e19b9ded Mon Sep 17 00:00:00 2001
From: Yosyp Buchma <josephbuchma@gmail.com>
Date: Mon, 18 Sep 2023 17:35:58 +0300
Subject: [PATCH] Concurrent GetTableColumnsMetaData for MySQL

---
 generator/mysql/query_set.go | 39 ++++++++++++++++++++++++++++++++----
 1 file changed, 35 insertions(+), 4 deletions(-)

diff --git a/generator/mysql/query_set.go b/generator/mysql/query_set.go
index 442b74b..95d6a93 100644
--- a/generator/mysql/query_set.go
+++ b/generator/mysql/query_set.go
@@ -4,7 +4,9 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"runtime"
 	"strings"
+	"sync"
 
 	"github.com/go-jet/jet/v2/generator/metadata"
 	"github.com/go-jet/jet/v2/qrm"
@@ -27,11 +29,40 @@ ORDER BY table_name;
 		return nil, fmt.Errorf("failed to query %s metadata result: %w", tableType, err)
 	}
 
+	tblChan := make(chan int, len(tables))
+	errChan := make(chan error, 1)
+
+	wg := sync.WaitGroup{}
+	for i := 0; i < runtime.NumCPU(); i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			var err1 error
+			for tblIdx := range tblChan {
+				tables[tblIdx].Columns, err1 = m.GetTableColumnsMetaData(db, schemaName, tables[tblIdx].Name)
+				if err1 != nil {
+					select {
+					case errChan <- fmt.Errorf("failed to get '%s' table columns metadata: %w", tables[tblIdx].Name, err1):
+						return
+					default:
+					}
+					return
+				}
+			}
+		}()
+	}
+
 	for i := range tables {
-		tables[i].Columns, err = m.GetTableColumnsMetaData(db, schemaName, tables[i].Name)
-		if err != nil {
-			return nil, fmt.Errorf("failed to get '%s' table columns metadata: %w", tables[i].Name, err)
-		}
+		tblChan <- i
+	}
+
+	close(tblChan)
+	wg.Wait()
+
+	select {
+	case err = <-errChan:
+		return nil, err
+	default:
 	}
 
 	return tables, nil