From 843c74f960dfaa104bc0fcac26febac9a975f999 Mon Sep 17 00:00:00 2001
From: Arthur Neves <arthurnn@gmail.com>
Date: Fri, 21 Jul 2017 15:37:57 -0400
Subject: [PATCH] Add a force-table-names command flag

usage example:
```
gh-ost  ...  --force-table-names=migration_tbl
```

The force-table-names flag will receive a table name and use that name
when creating the _del, _gho, _ghc tables.
For instance for that example above, the tables would be:

_migration_tbl_del
_migration_tbl_gho
_migration_tbl_ghc

[fixes #399]
---
 go/base/context.go      | 26 ++++++++++++++++++++++----
 go/base/context_test.go |  8 ++++++++
 go/cmd/gh-ost/main.go   |  1 +
 3 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/go/base/context.go b/go/base/context.go
index 8077e22..fff040e 100644
--- a/go/base/context.go
+++ b/go/base/context.go
@@ -192,6 +192,7 @@ type MigrationContext struct {
 	Iteration                        int64
 	MigrationIterationRangeMinValues *sql.ColumnValues
 	MigrationIterationRangeMaxValues *sql.ColumnValues
+	ForceTmpTableName                string
 
 	recentBinlogCoordinates mysql.BinlogCoordinates
 
@@ -253,25 +254,42 @@ func getSafeTableName(baseName string, suffix string) string {
 }
 
 // GetGhostTableName generates the name of ghost table, based on original table name
+// or a given table name
 func (this *MigrationContext) GetGhostTableName() string {
-	return getSafeTableName(this.OriginalTableName, "gho")
+	if this.ForceTmpTableName != "" {
+		return getSafeTableName(this.ForceTmpTableName, "gho")
+	} else {
+		return getSafeTableName(this.OriginalTableName, "gho")
+	}
 }
 
 // GetOldTableName generates the name of the "old" table, into which the original table is renamed.
 func (this *MigrationContext) GetOldTableName() string {
+	var tableName string
+	if this.ForceTmpTableName != "" {
+		tableName = this.ForceTmpTableName
+	} else {
+		tableName = this.OriginalTableName
+	}
+
 	if this.TimestampOldTable {
 		t := this.StartTime
 		timestamp := fmt.Sprintf("%d%02d%02d%02d%02d%02d",
 			t.Year(), t.Month(), t.Day(),
 			t.Hour(), t.Minute(), t.Second())
-		return getSafeTableName(this.OriginalTableName, fmt.Sprintf("%s_del", timestamp))
+		return getSafeTableName(tableName, fmt.Sprintf("%s_del", timestamp))
 	}
-	return getSafeTableName(this.OriginalTableName, "del")
+	return getSafeTableName(tableName, "del")
 }
 
 // GetChangelogTableName generates the name of changelog table, based on original table name
+// or a given table name.
 func (this *MigrationContext) GetChangelogTableName() string {
-	return getSafeTableName(this.OriginalTableName, "ghc")
+	if this.ForceTmpTableName != "" {
+		return getSafeTableName(this.ForceTmpTableName, "ghc")
+	} else {
+		return getSafeTableName(this.OriginalTableName, "ghc")
+	}
 }
 
 // GetVoluntaryLockName returns a name of a voluntary lock to be used throughout
diff --git a/go/base/context_test.go b/go/base/context_test.go
index b9e87d6..90a8d21 100644
--- a/go/base/context_test.go
+++ b/go/base/context_test.go
@@ -44,4 +44,12 @@ func TestGetTableNames(t *testing.T) {
 		oldTableName := context.GetOldTableName()
 		test.S(t).ExpectEquals(oldTableName, "_a1234567890123456789012345678901234567890123_20130203195400_del")
 	}
+	{
+		context.OriginalTableName = "foo_bar_baz"
+		context.ForceTmpTableName = "tmp"
+		context.TimestampOldTable = false
+		test.S(t).ExpectEquals(context.GetOldTableName(), "_tmp_del")
+		test.S(t).ExpectEquals(context.GetGhostTableName(), "_tmp_gho")
+		test.S(t).ExpectEquals(context.GetChangelogTableName(), "_tmp_ghc")
+	}
 }
diff --git a/go/cmd/gh-ost/main.go b/go/cmd/gh-ost/main.go
index a4f4f3e..7aabe81 100644
--- a/go/cmd/gh-ost/main.go
+++ b/go/cmd/gh-ost/main.go
@@ -120,6 +120,7 @@ func main() {
 	help := flag.Bool("help", false, "Display usage")
 	version := flag.Bool("version", false, "Print version & exit")
 	checkFlag := flag.Bool("check-flag", false, "Check if another flag exists/supported. This allows for cross-version scripting. Exits with 0 when all additional provided flags exist, nonzero otherwise. You must provide (dummy) values for flags that require a value. Example: gh-ost --check-flag --cut-over-lock-timeout-seconds --nice-ratio 0")
+	flag.StringVar(&migrationContext.ForceTmpTableName, "force-table-names", "", "table name prefix to be used on the temporary tables")
 
 	flag.Parse()