From 72f63d30420c56d1155ca3cf9dfecc196cdffcc2 Mon Sep 17 00:00:00 2001
From: Shlomi Noach <shlomi-noach@github.com>
Date: Tue, 4 Oct 2016 21:18:44 +0200
Subject: [PATCH 01/10] safe access to applier/inspector hostnames for hooks

---
 go/base/context.go | 22 ++++++++++++++++++++++
 go/logic/hooks.go  |  4 ++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/go/base/context.go b/go/base/context.go
index 41aa915..b5809a2 100644
--- a/go/base/context.go
+++ b/go/base/context.go
@@ -236,6 +236,28 @@ func (this *MigrationContext) RequiresBinlogFormatChange() bool {
 	return this.OriginalBinlogFormat != "ROW"
 }
 
+// GetApplierHostname is a safe access method to the applier hostname
+func (this *MigrationContext) GetApplierHostname() string {
+	if this.ApplierConnectionConfig == nil {
+		return ""
+	}
+	if this.ApplierConnectionConfig.ImpliedKey == nil {
+		return ""
+	}
+	return this.ApplierConnectionConfig.ImpliedKey.Hostname
+}
+
+// GetInspectorHostname is a safe access method to the inspector hostname
+func (this *MigrationContext) GetInspectorHostname() string {
+	if this.InspectorConnectionConfig == nil {
+		return ""
+	}
+	if this.InspectorConnectionConfig.ImpliedKey == nil {
+		return ""
+	}
+	return this.InspectorConnectionConfig.ImpliedKey.Hostname
+}
+
 // InspectorIsAlsoApplier is `true` when the both inspector and applier are the
 // same database instance. This would be true when running directly on master or when
 // testing on replica.
diff --git a/go/logic/hooks.go b/go/logic/hooks.go
index d288218..25d745a 100644
--- a/go/logic/hooks.go
+++ b/go/logic/hooks.go
@@ -59,8 +59,8 @@ func (this *HooksExecutor) applyEnvironmentVairables(extraVariables ...string) [
 	env = append(env, fmt.Sprintf("GH_OST_ESTIMATED_ROWS=%d", estimatedRows))
 	totalRowsCopied := this.migrationContext.GetTotalRowsCopied()
 	env = append(env, fmt.Sprintf("GH_OST_COPIED_ROWS=%d", totalRowsCopied))
-	env = append(env, fmt.Sprintf("GH_OST_MIGRATED_HOST=%s", this.migrationContext.ApplierConnectionConfig.ImpliedKey.Hostname))
-	env = append(env, fmt.Sprintf("GH_OST_INSPECTED_HOST=%s", this.migrationContext.InspectorConnectionConfig.ImpliedKey.Hostname))
+	env = append(env, fmt.Sprintf("GH_OST_MIGRATED_HOST=%s", this.migrationContext.GetApplierHostname()))
+	env = append(env, fmt.Sprintf("GH_OST_INSPECTED_HOST=%s", this.migrationContext.GetInspectorHostname()))
 	env = append(env, fmt.Sprintf("GH_OST_EXECUTING_HOST=%s", this.migrationContext.Hostname))
 	env = append(env, fmt.Sprintf("GH_OST_HOOKS_HINT=%s", this.migrationContext.HooksHintMessage))
 

From ef04fa49f5ba4e5a1f46a4f6ea6779e6d6cf77f6 Mon Sep 17 00:00:00 2001
From: Shlomi Noach <shlomi-noach@github.com>
Date: Thu, 6 Oct 2016 12:00:34 +0200
Subject: [PATCH 02/10] assume-master-host now applied ImpliedKey

---
 go/logic/migrator.go | 1 +
 1 file changed, 1 insertion(+)

diff --git a/go/logic/migrator.go b/go/logic/migrator.go
index 2ac4c37..32466d2 100644
--- a/go/logic/migrator.go
+++ b/go/logic/migrator.go
@@ -624,6 +624,7 @@ func (this *Migrator) initiateInspector() (err error) {
 			return err
 		} else {
 			this.migrationContext.ApplierConnectionConfig.Key = *key
+			this.migrationContext.ApplierConnectionConfig.ImpliedKey = key
 		}
 	}
 	if this.migrationContext.TestOnReplica || this.migrationContext.MigrateOnReplica {

From 1f65473e691b05e7d60e09300d8102a89485d228 Mon Sep 17 00:00:00 2001
From: Shlomi Noach <shlomi-noach@github.com>
Date: Fri, 7 Oct 2016 10:20:50 +0200
Subject: [PATCH 03/10] support for --discard-foreign-keys This flag makes
 migration silently and happily discard any existing foreign keys on migrated
 table. This is useful for intentional dropping of foreign keys, as gh-ost
 does not otherwise have support for foreign key migration. At some time in
 the future gh-ost may support foreign key migration, at which time this flag
 will be removed

---
 go/base/context.go    |  1 +
 go/cmd/gh-ost/main.go |  1 +
 go/logic/inspect.go   | 12 ++++++++----
 3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/go/base/context.go b/go/base/context.go
index 41aa915..1052335 100644
--- a/go/base/context.go
+++ b/go/base/context.go
@@ -70,6 +70,7 @@ type MigrationContext struct {
 	ApproveRenamedColumns    bool
 	SkipRenamedColumns       bool
 	IsTungsten               bool
+	DiscardForeignKeys       bool
 
 	config      ContextConfig
 	configMutex *sync.Mutex
diff --git a/go/cmd/gh-ost/main.go b/go/cmd/gh-ost/main.go
index 9231269..a87d5d7 100644
--- a/go/cmd/gh-ost/main.go
+++ b/go/cmd/gh-ost/main.go
@@ -61,6 +61,7 @@ func main() {
 	flag.BoolVar(&migrationContext.ApproveRenamedColumns, "approve-renamed-columns", false, "in case your `ALTER` statement renames columns, gh-ost will note that and offer its interpretation of the rename. By default gh-ost does not proceed to execute. This flag approves that gh-ost's interpretation si correct")
 	flag.BoolVar(&migrationContext.SkipRenamedColumns, "skip-renamed-columns", false, "in case your `ALTER` statement renames columns, gh-ost will note that and offer its interpretation of the rename. By default gh-ost does not proceed to execute. This flag tells gh-ost to skip the renamed columns, i.e. to treat what gh-ost thinks are renamed columns as unrelated columns. NOTE: you may lose column data")
 	flag.BoolVar(&migrationContext.IsTungsten, "tungsten", false, "explicitly let gh-ost know that you are running on a tungsten-replication based topology (you are likely to also provide --assume-master-host)")
+	flag.BoolVar(&migrationContext.DiscardForeignKeys, "discard-foreign-keys", false, "DANGER! This flag will migrate a table that has foreign keys and will NOT create foreign keys on the ghost table, thus your altered table will have NO foreign keys. This is useful for intentional dropping of foreign keys")
 
 	executeFlag := flag.Bool("execute", false, "actually execute the alter & migrate the table. Default is noop: do some tests and exit")
 	flag.BoolVar(&migrationContext.TestOnReplica, "test-on-replica", false, "Have the migration run on a replica, not on the master. At the end of migration replication is stopped, and tables are swapped and immediately swap-revert. Replication remains stopped and you can compare the two tables for building trust")
diff --git a/go/logic/inspect.go b/go/logic/inspect.go
index 28d1884..ecd1bbc 100644
--- a/go/logic/inspect.go
+++ b/go/logic/inspect.go
@@ -375,11 +375,15 @@ func (this *Inspector) validateTableForeignKeys() error {
 	if err != nil {
 		return err
 	}
-	if numForeignKeys > 0 {
-		return log.Errorf("Found %d foreign keys related to %s.%s. Foreign keys are not supported. Bailing out", numForeignKeys, sql.EscapeName(this.migrationContext.DatabaseName), sql.EscapeName(this.migrationContext.OriginalTableName))
+	if numForeignKeys == 0 {
+		log.Debugf("Validated no foreign keys exist on table")
+		return nil
 	}
-	log.Debugf("Validated no foreign keys exist on table")
-	return nil
+	if this.migrationContext.DiscardForeignKeys {
+		log.Debugf("Foreign keys found and will be dropped, as per given --discard-foreign-keys flag")
+		return nil
+	}
+	return log.Errorf("Found %d foreign keys related to %s.%s. Foreign keys are not supported. Bailing out", numForeignKeys, sql.EscapeName(this.migrationContext.DatabaseName), sql.EscapeName(this.migrationContext.OriginalTableName))
 }
 
 // validateTableTriggers makes sure no triggers exist on the migrated table

From 5d312a2bfb383c85797b0b945d0cfd8272bc8c54 Mon Sep 17 00:00:00 2001
From: Shlomi Noach <shlomi-noach@github.com>
Date: Fri, 7 Oct 2016 10:23:52 +0200
Subject: [PATCH 04/10] documenting --discard-foreign-keys flag

---
 build.sh                  | 2 +-
 doc/command-line-flags.md | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/build.sh b/build.sh
index 8b09426..3b8dc4b 100755
--- a/build.sh
+++ b/build.sh
@@ -2,7 +2,7 @@
 #
 #
 
-RELEASE_VERSION="1.0.20"
+RELEASE_VERSION="1.0.21"
 
 function build {
     osname=$1
diff --git a/doc/command-line-flags.md b/doc/command-line-flags.md
index 827ce96..2ead87f 100644
--- a/doc/command-line-flags.md
+++ b/doc/command-line-flags.md
@@ -47,6 +47,12 @@ See `exact-rowcount`
 
 Optional. Default is `safe`. See more discussion in [cut-over](cut-over.md)
 
+### discard-foreign-keys
+
+**Danger**: this flag will _silently_ discard any foreign keys existing on your table.
+
+At this time (10-2016) `gh-ost` does not support foreign keys on migrated tables (it bails out when it notices a FK on the migrated table). However, it is able to support _dropping_ of foreign keys via this flag. If you're trying to get rid of foreign keys in your environment, this is a useful flag.
+
 ### exact-rowcount
 
 A `gh-ost` execution need to copy whatever rows you have in your existing table onto the ghost table. This can, and often be, a large number. Exactly what that number is?

From 8e5c9cd5e178df7d646b087840ce6eecb5156c6b Mon Sep 17 00:00:00 2001
From: Shlomi Noach <shlomi-noach@github.com>
Date: Sat, 8 Oct 2016 11:07:01 +0200
Subject: [PATCH 05/10] adding fk tests

---
 localtests/discard-fk/create.sql | 31 +++++++++++++++++++++++++++++++
 localtests/discard-fk/extra_args |  1 +
 2 files changed, 32 insertions(+)
 create mode 100644 localtests/discard-fk/create.sql
 create mode 100644 localtests/discard-fk/extra_args

diff --git a/localtests/discard-fk/create.sql b/localtests/discard-fk/create.sql
new file mode 100644
index 0000000..557287c
--- /dev/null
+++ b/localtests/discard-fk/create.sql
@@ -0,0 +1,31 @@
+drop table if exists gh_ost_test;
+drop table if exists gh_ost_test_fk_parent;
+create table gh_ost_test_fk_parent (
+  id int auto_increment,
+  ts timestamp,
+  primary key(id)
+);
+create table gh_ost_test (
+  id int auto_increment,
+  i int not null,
+  parent_id int not null,
+  primary key(id),
+  constraint test_fk foreign key (parent_id) references gh_ost_test_fk_parent (id) on delete no action
+) auto_increment=1;
+
+insert into gh_ost_test_fk_parent (id) values (1),(2),(3);
+
+drop event if exists gh_ost_test;
+delimiter ;;
+create event gh_ost_test
+  on schedule every 1 second
+  starts current_timestamp
+  ends current_timestamp + interval 60 second
+  on completion not preserve
+  enable
+  do
+begin
+  insert into gh_ost_test values (null, 11, 1);
+  insert into gh_ost_test values (null, 13, 2);
+  insert into gh_ost_test values (null, 17, 3);
+end ;;
diff --git a/localtests/discard-fk/extra_args b/localtests/discard-fk/extra_args
new file mode 100644
index 0000000..2d00c49
--- /dev/null
+++ b/localtests/discard-fk/extra_args
@@ -0,0 +1 @@
+--discard-foreign-keys

From 56e0833389c4eb3a492ba74003dd46d6852a7fb5 Mon Sep 17 00:00:00 2001
From: Shlomi Noach <shlomi-noach@github.com>
Date: Mon, 10 Oct 2016 12:28:13 +0200
Subject: [PATCH 06/10] support for expect_failure on localtests

---
 localtests/test.sh | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/localtests/test.sh b/localtests/test.sh
index f12b66f..fc0c9b6 100755
--- a/localtests/test.sh
+++ b/localtests/test.sh
@@ -95,7 +95,18 @@ test_single() {
   echo_dot
   bash $exec_command_file 1> $test_logfile 2>&1
 
-  if [ $? -ne 0 ] ; then
+  execution_result=$?
+
+  if [ -f $tests_path/$test_name/expect_failure ] ; then
+    if [ $execution_result -eq 0 ] ; then
+      echo
+      echo "ERROR $test_name execution was expected to exit on error but did not. cat $test_logfile"
+      return 1
+    fi
+    return 0
+  fi
+
+  if [ $execution_result -ne 0 ] ; then
     echo
     echo "ERROR $test_name execution failure. cat $test_logfile"
     return 1

From a4d566e71c5bdfc6cb7dddf8f35e27581844fe27 Mon Sep 17 00:00:00 2001
From: Shlomi Noach <shlomi-noach@github.com>
Date: Mon, 10 Oct 2016 12:28:56 +0200
Subject: [PATCH 07/10] counting child vs parent sie foreign keys on table,
 parent-side foreign keys cannot be discarded

---
 go/logic/inspect.go | 40 ++++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/go/logic/inspect.go b/go/logic/inspect.go
index ecd1bbc..eae0e24 100644
--- a/go/logic/inspect.go
+++ b/go/logic/inspect.go
@@ -63,7 +63,7 @@ func (this *Inspector) ValidateOriginalTable() (err error) {
 	if err := this.validateTable(); err != nil {
 		return err
 	}
-	if err := this.validateTableForeignKeys(); err != nil {
+	if err := this.validateTableForeignKeys(this.migrationContext.DiscardForeignKeys); err != nil {
 		return err
 	}
 	if err := this.validateTableTriggers(); err != nil {
@@ -349,9 +349,11 @@ func (this *Inspector) validateTable() error {
 }
 
 // validateTableForeignKeys makes sure no foreign keys exist on the migrated table
-func (this *Inspector) validateTableForeignKeys() error {
+func (this *Inspector) validateTableForeignKeys(allowChildForeignKeys bool) error {
 	query := `
-		SELECT TABLE_SCHEMA, TABLE_NAME
+		SELECT
+			SUM(REFERENCED_TABLE_NAME IS NOT NULL AND TABLE_SCHEMA=? AND TABLE_NAME=?) as num_child_side_fk,
+			SUM(REFERENCED_TABLE_NAME IS NOT NULL AND REFERENCED_TABLE_SCHEMA=? AND REFERENCED_TABLE_NAME=?) as num_parent_side_fk
 		FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
 		WHERE
 				REFERENCED_TABLE_NAME IS NOT NULL
@@ -359,31 +361,37 @@ func (this *Inspector) validateTableForeignKeys() error {
 					OR (REFERENCED_TABLE_SCHEMA=? AND REFERENCED_TABLE_NAME=?)
 				)
 	`
-	numForeignKeys := 0
-	err := sqlutils.QueryRowsMap(this.db, query, func(rowMap sqlutils.RowMap) error {
-		fkSchema := rowMap.GetString("TABLE_SCHEMA")
-		fkTable := rowMap.GetString("TABLE_NAME")
-		log.Infof("Found foreign key on %s.%s related to %s.%s", sql.EscapeName(fkSchema), sql.EscapeName(fkTable), sql.EscapeName(this.migrationContext.DatabaseName), sql.EscapeName(this.migrationContext.OriginalTableName))
-		numForeignKeys++
+	numParentForeignKeys := 0
+	numChildForeignKeys := 0
+	err := sqlutils.QueryRowsMap(this.db, query, func(m sqlutils.RowMap) error {
+		numChildForeignKeys = m.GetInt("num_child_side_fk")
+		numParentForeignKeys = m.GetInt("num_parent_side_fk")
 		return nil
 	},
 		this.migrationContext.DatabaseName,
 		this.migrationContext.OriginalTableName,
 		this.migrationContext.DatabaseName,
 		this.migrationContext.OriginalTableName,
+		this.migrationContext.DatabaseName,
+		this.migrationContext.OriginalTableName,
+		this.migrationContext.DatabaseName,
+		this.migrationContext.OriginalTableName,
 	)
 	if err != nil {
 		return err
 	}
-	if numForeignKeys == 0 {
-		log.Debugf("Validated no foreign keys exist on table")
-		return nil
+	if numParentForeignKeys > 0 {
+		return log.Errorf("Found %d parent-side foreign keys on %s.%s. Parent-side foreign keys are not supported. Bailing out", numParentForeignKeys, sql.EscapeName(this.migrationContext.DatabaseName), sql.EscapeName(this.migrationContext.OriginalTableName))
 	}
-	if this.migrationContext.DiscardForeignKeys {
-		log.Debugf("Foreign keys found and will be dropped, as per given --discard-foreign-keys flag")
-		return nil
+	if numChildForeignKeys > 0 {
+		if allowChildForeignKeys {
+			log.Debugf("Foreign keys found and will be dropped, as per given --discard-foreign-keys flag")
+			return nil
+		}
+		return log.Errorf("Found %d child-side foreign keys on %s.%s. Child-side foreign keys are not supported. Bailing out", numChildForeignKeys, sql.EscapeName(this.migrationContext.DatabaseName), sql.EscapeName(this.migrationContext.OriginalTableName))
 	}
-	return log.Errorf("Found %d foreign keys related to %s.%s. Foreign keys are not supported. Bailing out", numForeignKeys, sql.EscapeName(this.migrationContext.DatabaseName), sql.EscapeName(this.migrationContext.OriginalTableName))
+	log.Debugf("Validated no foreign keys exist on table")
+	return nil
 }
 
 // validateTableTriggers makes sure no triggers exist on the migrated table

From 4d4af0729516a0966ed83ae78cb3724e2a677b46 Mon Sep 17 00:00:00 2001
From: Shlomi Noach <shlomi-noach@github.com>
Date: Mon, 10 Oct 2016 12:29:25 +0200
Subject: [PATCH 08/10] more tests for foreign keys, including expected
 failures

---
 localtests/discard-fk/create.sql         |  1 +
 localtests/fail-fk-parent/create.sql     | 41 ++++++++++++++++++++++++
 localtests/fail-fk-parent/expect_failure |  0
 localtests/fail-fk-parent/extra_args     |  1 +
 localtests/fail-fk/create.sql            | 32 ++++++++++++++++++
 localtests/fail-fk/expect_failure        |  0
 6 files changed, 75 insertions(+)
 create mode 100644 localtests/fail-fk-parent/create.sql
 create mode 100644 localtests/fail-fk-parent/expect_failure
 create mode 100644 localtests/fail-fk-parent/extra_args
 create mode 100644 localtests/fail-fk/create.sql
 create mode 100644 localtests/fail-fk/expect_failure

diff --git a/localtests/discard-fk/create.sql b/localtests/discard-fk/create.sql
index 557287c..6ef2d5c 100644
--- a/localtests/discard-fk/create.sql
+++ b/localtests/discard-fk/create.sql
@@ -1,3 +1,4 @@
+drop table if exists gh_ost_test_child;
 drop table if exists gh_ost_test;
 drop table if exists gh_ost_test_fk_parent;
 create table gh_ost_test_fk_parent (
diff --git a/localtests/fail-fk-parent/create.sql b/localtests/fail-fk-parent/create.sql
new file mode 100644
index 0000000..ec713d6
--- /dev/null
+++ b/localtests/fail-fk-parent/create.sql
@@ -0,0 +1,41 @@
+drop table if exists gh_ost_test_child;
+drop table if exists gh_ost_test;
+create table gh_ost_test (
+  id int auto_increment,
+  primary key(id)
+) engine=innodb auto_increment=1;
+
+create table gh_ost_test_child (
+  id int auto_increment,
+  i int not null,
+  parent_id int not null,
+  constraint test_fk foreign key (parent_id) references gh_ost_test (id) on delete no action,
+  primary key(id)
+) engine=innodb;
+insert into gh_ost_test (id) values (1),(2),(3);
+
+drop event if exists gh_ost_test;
+drop event if exists gh_ost_test_cleanup;
+
+delimiter ;;
+create event gh_ost_test
+  on schedule every 1 second
+  starts current_timestamp
+  ends current_timestamp + interval 60 second
+  on completion not preserve
+  enable
+  do
+begin
+  insert into gh_ost_test_child values (null, 11, 1);
+  insert into gh_ost_test_child values (null, 13, 2);
+  insert into gh_ost_test_child values (null, 17, 3);
+end ;;
+
+create event gh_ost_test_cleanup
+  on schedule at current_timestamp + interval 60 second
+  on completion not preserve
+  enable
+  do
+begin
+  drop table if exists gh_ost_test_child;
+end ;;
diff --git a/localtests/fail-fk-parent/expect_failure b/localtests/fail-fk-parent/expect_failure
new file mode 100644
index 0000000..e69de29
diff --git a/localtests/fail-fk-parent/extra_args b/localtests/fail-fk-parent/extra_args
new file mode 100644
index 0000000..2d00c49
--- /dev/null
+++ b/localtests/fail-fk-parent/extra_args
@@ -0,0 +1 @@
+--discard-foreign-keys
diff --git a/localtests/fail-fk/create.sql b/localtests/fail-fk/create.sql
new file mode 100644
index 0000000..6ef2d5c
--- /dev/null
+++ b/localtests/fail-fk/create.sql
@@ -0,0 +1,32 @@
+drop table if exists gh_ost_test_child;
+drop table if exists gh_ost_test;
+drop table if exists gh_ost_test_fk_parent;
+create table gh_ost_test_fk_parent (
+  id int auto_increment,
+  ts timestamp,
+  primary key(id)
+);
+create table gh_ost_test (
+  id int auto_increment,
+  i int not null,
+  parent_id int not null,
+  primary key(id),
+  constraint test_fk foreign key (parent_id) references gh_ost_test_fk_parent (id) on delete no action
+) auto_increment=1;
+
+insert into gh_ost_test_fk_parent (id) values (1),(2),(3);
+
+drop event if exists gh_ost_test;
+delimiter ;;
+create event gh_ost_test
+  on schedule every 1 second
+  starts current_timestamp
+  ends current_timestamp + interval 60 second
+  on completion not preserve
+  enable
+  do
+begin
+  insert into gh_ost_test values (null, 11, 1);
+  insert into gh_ost_test values (null, 13, 2);
+  insert into gh_ost_test values (null, 17, 3);
+end ;;
diff --git a/localtests/fail-fk/expect_failure b/localtests/fail-fk/expect_failure
new file mode 100644
index 0000000..e69de29

From c1a6773c029b8eab6a493633ab8c12850bdfd872 Mon Sep 17 00:00:00 2001
From: Shlomi Noach <shlomi-noach@github.com>
Date: Tue, 11 Oct 2016 16:42:19 +0200
Subject: [PATCH 09/10] better handling of --assume-master-host separated logic
 and not even attempting to crawl topology

---
 go/logic/migrator.go        | 24 +++++++++-------
 go/mysql/connection.go      | 12 ++++----
 go/mysql/connection_test.go | 57 +++++++++++++++++++++++++++++++++++++
 3 files changed, 78 insertions(+), 15 deletions(-)
 create mode 100644 go/mysql/connection_test.go

diff --git a/go/logic/migrator.go b/go/logic/migrator.go
index 32466d2..7c96871 100644
--- a/go/logic/migrator.go
+++ b/go/logic/migrator.go
@@ -616,17 +616,22 @@ func (this *Migrator) initiateInspector() (err error) {
 	}
 	// So far so good, table is accessible and valid.
 	// Let's get master connection config
-	if this.migrationContext.ApplierConnectionConfig, err = this.inspector.getMasterConnectionConfig(); err != nil {
-		return err
-	}
-	if this.migrationContext.AssumeMasterHostname != "" {
-		if key, err := mysql.ParseRawInstanceKeyLoose(this.migrationContext.AssumeMasterHostname); err != nil {
+	if this.migrationContext.AssumeMasterHostname == "" {
+		// No forced master host; detect master
+		if this.migrationContext.ApplierConnectionConfig, err = this.inspector.getMasterConnectionConfig(); err != nil {
 			return err
-		} else {
-			this.migrationContext.ApplierConnectionConfig.Key = *key
-			this.migrationContext.ApplierConnectionConfig.ImpliedKey = key
 		}
+		log.Infof("Master found to be %+v", *this.migrationContext.ApplierConnectionConfig.ImpliedKey)
+	} else {
+		// Forced master host.
+		key, err := mysql.ParseRawInstanceKeyLoose(this.migrationContext.AssumeMasterHostname)
+		if err != nil {
+			return err
+		}
+		this.migrationContext.ApplierConnectionConfig = this.migrationContext.InspectorConnectionConfig.DuplicateCredentials(*key)
+		log.Infof("Master forced to be %+v", *this.migrationContext.ApplierConnectionConfig.ImpliedKey)
 	}
+	// validate configs
 	if this.migrationContext.TestOnReplica || this.migrationContext.MigrateOnReplica {
 		if this.migrationContext.InspectorIsAlsoApplier() {
 			return fmt.Errorf("Instructed to --test-on-replica or --migrate-on-replica, but the server we connect to doesn't seem to be a replica")
@@ -639,13 +644,12 @@ func (this *Migrator) initiateInspector() (err error) {
 			this.migrationContext.AddThrottleControlReplicaKey(this.migrationContext.InspectorConnectionConfig.Key)
 		}
 	} else if this.migrationContext.InspectorIsAlsoApplier() && !this.migrationContext.AllowedRunningOnMaster {
-		return fmt.Errorf("It seems like this migration attempt to run directly on master. Preferably it would be executed on a replica (and this reduces load from the master). To proceed please provide --allow-on-master")
+		return fmt.Errorf("It seems like this migration attempt to run directly on master. Preferably it would be executed on a replica (and this reduces load from the master). To proceed please provide --allow-on-master. Inspector config=%+v, applier config=%+v", this.migrationContext.InspectorConnectionConfig, this.migrationContext.ApplierConnectionConfig)
 	}
 	if err := this.inspector.validateLogSlaveUpdates(); err != nil {
 		return err
 	}
 
-	log.Infof("Master found to be %+v", *this.migrationContext.ApplierConnectionConfig.ImpliedKey)
 	return nil
 }
 
diff --git a/go/mysql/connection.go b/go/mysql/connection.go
index 649da93..daae75e 100644
--- a/go/mysql/connection.go
+++ b/go/mysql/connection.go
@@ -26,12 +26,10 @@ func NewConnectionConfig() *ConnectionConfig {
 	return config
 }
 
-func (this *ConnectionConfig) Duplicate() *ConnectionConfig {
+// DuplicateCredentials creates a new connection config with given key and with same credentials as this config
+func (this *ConnectionConfig) DuplicateCredentials(key InstanceKey) *ConnectionConfig {
 	config := &ConnectionConfig{
-		Key: InstanceKey{
-			Hostname: this.Key.Hostname,
-			Port:     this.Key.Port,
-		},
+		Key:      key,
 		User:     this.User,
 		Password: this.Password,
 	}
@@ -39,6 +37,10 @@ func (this *ConnectionConfig) Duplicate() *ConnectionConfig {
 	return config
 }
 
+func (this *ConnectionConfig) Duplicate() *ConnectionConfig {
+	return this.DuplicateCredentials(this.Key)
+}
+
 func (this *ConnectionConfig) String() string {
 	return fmt.Sprintf("%s, user=%s", this.Key.DisplayString(), this.User)
 }
diff --git a/go/mysql/connection_test.go b/go/mysql/connection_test.go
new file mode 100644
index 0000000..657feb0
--- /dev/null
+++ b/go/mysql/connection_test.go
@@ -0,0 +1,57 @@
+/*
+   Copyright 2016 GitHub Inc.
+	 See https://github.com/github/gh-ost/blob/master/LICENSE
+*/
+
+package mysql
+
+import (
+	"testing"
+
+	"github.com/outbrain/golib/log"
+	test "github.com/outbrain/golib/tests"
+)
+
+func init() {
+	log.SetLevel(log.ERROR)
+}
+
+func TestNewConnectionConfig(t *testing.T) {
+	c := NewConnectionConfig()
+	test.S(t).ExpectEquals(c.Key.Hostname, "")
+	test.S(t).ExpectEquals(c.Key.Port, 0)
+	test.S(t).ExpectEquals(c.ImpliedKey.Hostname, "")
+	test.S(t).ExpectEquals(c.ImpliedKey.Port, 0)
+	test.S(t).ExpectEquals(c.User, "")
+	test.S(t).ExpectEquals(c.Password, "")
+}
+
+func TestDuplicateCredentials(t *testing.T) {
+	c := NewConnectionConfig()
+	c.Key = InstanceKey{Hostname: "myhost", Port: 3306}
+	c.User = "gromit"
+	c.Password = "penguin"
+
+	dup := c.DuplicateCredentials(InstanceKey{Hostname: "otherhost", Port: 3310})
+	test.S(t).ExpectEquals(dup.Key.Hostname, "otherhost")
+	test.S(t).ExpectEquals(dup.Key.Port, 3310)
+	test.S(t).ExpectEquals(dup.ImpliedKey.Hostname, "otherhost")
+	test.S(t).ExpectEquals(dup.ImpliedKey.Port, 3310)
+	test.S(t).ExpectEquals(dup.User, "gromit")
+	test.S(t).ExpectEquals(dup.Password, "penguin")
+}
+
+func TestDuplicate(t *testing.T) {
+	c := NewConnectionConfig()
+	c.Key = InstanceKey{Hostname: "myhost", Port: 3306}
+	c.User = "gromit"
+	c.Password = "penguin"
+
+	dup := c.Duplicate()
+	test.S(t).ExpectEquals(dup.Key.Hostname, "myhost")
+	test.S(t).ExpectEquals(dup.Key.Port, 3306)
+	test.S(t).ExpectEquals(dup.ImpliedKey.Hostname, "myhost")
+	test.S(t).ExpectEquals(dup.ImpliedKey.Port, 3306)
+	test.S(t).ExpectEquals(dup.User, "gromit")
+	test.S(t).ExpectEquals(dup.Password, "penguin")
+}

From c2801978219a4d9b44ac6835701b36221f5503ed Mon Sep 17 00:00:00 2001
From: Shlomi Noach <shlomi-noach@github.com>
Date: Tue, 11 Oct 2016 20:29:56 +0200
Subject: [PATCH 10/10] updated version

---
 build.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/build.sh b/build.sh
index 8b09426..3b8dc4b 100755
--- a/build.sh
+++ b/build.sh
@@ -2,7 +2,7 @@
 #
 #
 
-RELEASE_VERSION="1.0.20"
+RELEASE_VERSION="1.0.21"
 
 function build {
     osname=$1