From 56f1350347a6ae418c42feaf89ac9d175d11681d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20Canna=C3=B2?= <rene.cannao@gmail.com>
Date: Mon, 29 Apr 2024 04:48:36 +0000
Subject: [PATCH 1/5] Optimization on multiple_prepared_statements-t

multiple_prepared_statements-t.cpp is now multi-threaded
---
 .../tests/multiple_prepared_statements-t.cpp  | 287 ++++++++++++++----
 1 file changed, 220 insertions(+), 67 deletions(-)

diff --git a/test/tap/tests/multiple_prepared_statements-t.cpp b/test/tap/tests/multiple_prepared_statements-t.cpp
index ea3bed603..d88fad720 100644
--- a/test/tap/tests/multiple_prepared_statements-t.cpp
+++ b/test/tap/tests/multiple_prepared_statements-t.cpp
@@ -42,9 +42,12 @@ inline unsigned long long monotonic_time() {
 	return (((unsigned long long) ts.tv_sec) * 1000000) + (ts.tv_nsec / 1000);
 }
 
+#define NTHREADS 5
 #define NCONNS 6
 #define NPREP 15000
 #define PROGRESS 2000
+
+pthread_mutex_t mtx[NCONNS];
 MYSQL* conns[NCONNS];
 int ids[NCONNS*NPREP];
 MYSQL_STMT * stmts[NCONNS*NPREP];
@@ -125,6 +128,163 @@ int execute_stmt(int idx) {
 	return 0;
 }
 
+void * prepare_thread(void *arg) {
+	int thread_id = *(int *)arg;
+	for (int i=0; i<NCONNS; i++) {
+		for (int j=0; j<NPREP; j++) {
+			int idx=i*NPREP+j;
+			if (idx%NTHREADS == thread_id) {
+				if (idx%PROGRESS==(PROGRESS-1)) diag("Preparing statements. Progress: %d", idx+1);
+				pthread_mutex_lock(&mtx[i]);
+				if (prepare_stmt(idx,i)) exit(EXIT_FAILURE);
+				// excute every 7 stmt
+				if (idx%7==0) {
+					if (execute_stmt(idx)) exit(EXIT_FAILURE);
+				}
+				pthread_mutex_unlock(&mtx[i]);
+			}
+		}
+	}
+	return NULL;
+}
+
+void * execute1_thread(void *arg) {
+	int thread_id = *(int *)arg;
+	for (int i=0; i<NCONNS; i++) {
+		for (int j=0; j<NPREP; j++) {
+			int idx=i*NPREP+j;
+			if (idx%NTHREADS == thread_id) {
+				if (idx%PROGRESS==(PROGRESS-1)) diag("Executing statements in order 1. Progress: %d", idx+1);
+				pthread_mutex_lock(&mtx[i]);
+				if (execute_stmt(idx)) exit(EXIT_FAILURE);
+				pthread_mutex_unlock(&mtx[i]);
+			}
+		}
+	}
+	return NULL;
+}
+void * execute2_thread(void *arg) {
+	int thread_id = *(int *)arg;
+	int p=0; // we need a new counter because of the out of order
+	for (int j=0; j<NPREP; j++) {
+		for (int i=0; i<NCONNS; i++) {
+			int idx=i*NPREP+j;
+			if (idx%NTHREADS == thread_id) {
+				if (p%PROGRESS==(PROGRESS-1)) diag("Executing statements in order 2. Progress: %d", p+1);
+				pthread_mutex_lock(&mtx[i]);
+				if (execute_stmt(idx)) exit(EXIT_FAILURE);
+				pthread_mutex_unlock(&mtx[i]);
+			}
+			p++;
+		}
+	}
+	return NULL;
+}
+
+void * execute3_thread(void *arg) {
+	int thread_id = *(int *)arg;
+	for (int i=0; i<NCONNS; i++) {
+		for (int j=0; j<NPREP; j++) {
+			int idx=i*NPREP+j;
+			if (idx%NTHREADS == thread_id) {
+				if (idx%PROGRESS==(PROGRESS-1)) diag("Closing or executing statements, loop 1. Progress: %d", idx+1);
+				pthread_mutex_lock(&mtx[i]);
+				if (idx%4==3) {
+					int rc = mysql_stmt_close(stmts[idx]);
+					if (rc) {
+						diag("Failed to close stmt %d", idx);
+						exit(EXIT_FAILURE);
+					}
+					stmts[idx] = NULL;
+				} else {
+					if (execute_stmt(idx)) exit(EXIT_FAILURE);
+				}
+				pthread_mutex_unlock(&mtx[i]);
+			}
+		}
+	}
+	return NULL;
+}
+
+void * execute4_thread(void *arg) {
+	int thread_id = *(int *)arg;
+	for (int i=0; i<NCONNS; i++) {
+		for (int j=0; j<NPREP; j++) {
+			int idx=i*NPREP+j;
+			if (idx%NTHREADS == thread_id) {
+				if (idx%PROGRESS==(PROGRESS-1)) diag("Closing or executing statements, loop 2. Progress: %d", idx+1);
+				pthread_mutex_lock(&mtx[i]);
+				if (idx%4==3) {
+					// skip, already closed
+				} else if (idx%4==2) {
+					int rc = mysql_stmt_close(stmts[idx]);
+					if (rc) {
+						diag("Failed to close stmt %d", idx);
+						exit(EXIT_FAILURE);
+					}
+					stmts[idx] = NULL;
+				} else {
+					if (execute_stmt(idx)) exit(EXIT_FAILURE);
+				}
+				pthread_mutex_unlock(&mtx[i]);
+			}
+		}
+	}
+	return NULL;
+}
+
+void *execute5_thread(void *arg) {
+	int thread_id = *(int *)arg;
+	for (int i=0; i<NCONNS; i++) {
+		for (int j=0; j<NPREP; j++) {
+			int idx=i*NPREP+j;
+			if (idx%NTHREADS == thread_id) {
+				if (idx%PROGRESS==(PROGRESS-1)) diag("Execute and close the prepared statements left, loop 1. Progress: %d", idx+1);
+				pthread_mutex_lock(&mtx[i]);
+				if (stmts[idx] != NULL) {
+					if (idx%2==1) {
+						if (execute_stmt(idx)) exit(EXIT_FAILURE);
+						int rc = mysql_stmt_close(stmts[idx]);
+						if (rc) {
+							diag("Failed to close stmt %d", idx);
+							exit(EXIT_FAILURE);
+						}
+						stmts[idx] = NULL;
+					}
+				}
+				pthread_mutex_unlock(&mtx[i]);
+			}
+		}
+	}
+	return NULL;
+}
+
+void *execute6_thread(void *arg) {
+	int thread_id = *(int *)arg;
+	for (int i=0; i<NCONNS; i++) {
+		for (int j=0; j<NPREP; j++) {
+			int idx=i*NPREP+j;
+			if (idx%NTHREADS == thread_id) {
+				if (idx%PROGRESS==(PROGRESS-1)) diag("Execute and close the prepared statements left, loop 2. Progress: %d", idx+1);
+				pthread_mutex_lock(&mtx[i]);
+				if (stmts[idx] != NULL) {
+					if (idx%2==0) {
+						if (execute_stmt(idx)) exit(EXIT_FAILURE);
+						int rc = mysql_stmt_close(stmts[idx]);
+						if (rc) {
+							diag("Failed to close stmt %d", idx);
+							exit(EXIT_FAILURE);
+						}
+						stmts[idx] = NULL;
+					}
+				}
+				pthread_mutex_unlock(&mtx[i]);
+			}
+		}
+	}
+	return NULL;
+}
+
 int main(int argc, char** argv) {
 	CommandLine cl;
 
@@ -147,6 +307,10 @@ int main(int argc, char** argv) {
 		}
 	}
 
+	for (int i=0; i<NCONNS; i++) {
+		pthread_mutex_init(&mtx[i], NULL);
+	}
+
 	// ceating "random" ids in within a range 0..NPREP
 	diag("Creating IDs");
 	for (int i=0; i<NCONNS*NPREP; i++) {
@@ -158,17 +322,18 @@ int main(int argc, char** argv) {
 	}
 
 	diag("Preparing statements");
-	for (int i=0; i<NCONNS; i++) {
-		for (int j=0; j<NPREP; j++) {
-			int idx=i*NPREP+j;
-			if (idx%PROGRESS==(PROGRESS-1)) diag("Preparing statements. Progress: %d", idx+1);
-			if (prepare_stmt(idx,i)) return EXIT_FAILURE;
-			// excute every 7 stmt
-			if (idx%7==0) {
-				if (execute_stmt(idx)) return EXIT_FAILURE;
-			}
+	pthread_t thi[NTHREADS];
+	int tid[NTHREADS];
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		tid[i] = i;
+		if ( pthread_create(&thi[i], NULL, prepare_thread , &tid[i]) != 0 ) {
+			perror("Thread creation");
+			return EXIT_FAILURE;
 		}
 	}
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		pthread_join(thi[i], NULL);
+	}
 
 	{
 		int Stmt_Cached = get_Stmt_Cached(proxysql_admin);
@@ -177,57 +342,51 @@ int main(int argc, char** argv) {
 
 	// excute statements in order
 	diag("Executing statements in order");
-	for (int i=0; i<NCONNS; i++) {
-		for (int j=0; j<NPREP; j++) {
-			int idx=i*NPREP+j;
-			if (idx%PROGRESS==(PROGRESS-1)) diag("Executing statements in order 1. Progress: %d", idx+1);
-			if (execute_stmt(idx)) return EXIT_FAILURE;
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		if ( pthread_create(&thi[i], NULL, execute1_thread , &tid[i]) != 0 ) {
+			perror("Thread creation");
+			return EXIT_FAILURE;
 		}
 	}
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		pthread_join(thi[i], NULL);
+	}
 
 	// excute statements in different order
 	diag("Executing statements in different order");
-	int p=0; // we need a new counter because of the out of order
-	for (int j=0; j<NPREP; j++) {
-		for (int i=0; i<NCONNS; i++) {
-			int idx=i*NPREP+j;
-			if (p%PROGRESS==(PROGRESS-1)) diag("Executing statements in order 2. Progress: %d", p+1);
-			if (execute_stmt(idx)) return EXIT_FAILURE;
-			p++;
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		if ( pthread_create(&thi[i], NULL, execute2_thread , &tid[i]) != 0 ) {
+			perror("Thread creation");
+			return EXIT_FAILURE;
 		}
 	}
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		pthread_join(thi[i], NULL);
+	}
 
 	// close 1 of 4 prepared statements, execute the rest
-	for (int i=0; i<NCONNS*NPREP; i++) {
-		if (i%PROGRESS==(PROGRESS-1)) diag("Closing or executing statements, loop 1. Progress: %d", i+1);
-		if (i%4==3) {
-			int rc = mysql_stmt_close(stmts[i]);
-			if (rc) {
-				diag("Failed to close stmt %d", i);
-				return EXIT_FAILURE;
-			}
-			stmts[i] = NULL;
-		} else {
-			if (execute_stmt(i)) return EXIT_FAILURE;
+	diag("Executing statements in different order");
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		if ( pthread_create(&thi[i], NULL, execute3_thread , &tid[i]) != 0 ) {
+			perror("Thread creation");
+			return EXIT_FAILURE;
 		}
 	}
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		pthread_join(thi[i], NULL);
+	}
 
 	// close 1 of 4 prepared statements, skip 1 in 4, execute the rest
-	for (int i=0; i<NCONNS*NPREP; i++) {
-		if (i%PROGRESS==(PROGRESS-1)) diag("Closing or executing statements, loop 2. Progress: %d", i+1);
-		if (i%4==3) {
-			// skip, already closed
-		} else if (i%4==2) {
-			int rc = mysql_stmt_close(stmts[i]);
-			if (rc) {
-				diag("Failed to close stmt %d", i);
-				return EXIT_FAILURE;
-			}
-			stmts[i] = NULL;
-		} else {
-			if (execute_stmt(i)) return EXIT_FAILURE;
+	diag("Executing statements in different order");
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		if ( pthread_create(&thi[i], NULL, execute4_thread , &tid[i]) != 0 ) {
+			perror("Thread creation");
+			return EXIT_FAILURE;
 		}
 	}
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		pthread_join(thi[i], NULL);
+	}
 
 	// close half the connections without closing the prepared statements
 	for (int i=0; i<NCONNS; i+=2) {
@@ -240,34 +399,28 @@ int main(int argc, char** argv) {
 	}
 
 	// execute and close the prepared statements left, loop 1
-	for (int i=0; i<NCONNS*NPREP; i++) {
-		if (stmts[i] != NULL) {
-			if (i%2==1) {
-				if (execute_stmt(i)) return EXIT_FAILURE;
-				int rc = mysql_stmt_close(stmts[i]);
-				if (rc) {
-					diag("Failed to close stmt %d", i);
-					return EXIT_FAILURE;
-				}
-				stmts[i] = NULL;
-			}
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		if ( pthread_create(&thi[i], NULL, execute5_thread , &tid[i]) != 0 ) {
+			perror("Thread creation");
+			return EXIT_FAILURE;
 		}
 	}
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		pthread_join(thi[i], NULL);
+	}
+
+
 
 	// execute and close the prepared statements left, loop 2
-	for (int i=0; i<NCONNS*NPREP; i++) {
-		if (stmts[i] != NULL) {
-			if (i%2==0) {
-				if (execute_stmt(i)) return EXIT_FAILURE;
-				int rc = mysql_stmt_close(stmts[i]);
-				if (rc) {
-					diag("Failed to close stmt %d", i);
-					return EXIT_FAILURE;
-				}
-				stmts[i] = NULL;
-			}
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		if ( pthread_create(&thi[i], NULL, execute6_thread , &tid[i]) != 0 ) {
+			perror("Thread creation");
+			return EXIT_FAILURE;
 		}
 	}
+	for (unsigned int i=0; i<NTHREADS; i++) {
+		pthread_join(thi[i], NULL);
+	}
 
 	// Half of the connections were freed earlier. We only iterate the other
 	// half that has not been freed.

From 9818e1c084f80c20aa3137f6599191ed7f54e11c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20Canna=C3=B2?= <rene.cannao@gmail.com>
Date: Mon, 29 Apr 2024 06:48:33 +0000
Subject: [PATCH 2/5] Better randomize in set_testing-240-t

---
 test/tap/tests/set_testing-240-t.cpp | 5 +++--
 test/tap/tests/set_testing-240.h     | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/test/tap/tests/set_testing-240-t.cpp b/test/tap/tests/set_testing-240-t.cpp
index cacf8c005..f5e157dfa 100644
--- a/test/tap/tests/set_testing-240-t.cpp
+++ b/test/tap/tests/set_testing-240-t.cpp
@@ -116,7 +116,8 @@ std::unordered_map<std::string,var_counter> vars_counters;
 */
 
 void * my_conn_thread(void *arg) {
-	g_seed = time(NULL) ^ getpid() ^ pthread_self();
+	g_seed = monotonic_time() * pthread_self() + monotonic_time();
+	srand(g_seed);
 	unsigned int select_OK=0;
 	unsigned int select_ERR=0;
 	int i, j;
@@ -168,7 +169,7 @@ void * my_conn_thread(void *arg) {
 		int fr = rand();
 		int r1=fr%count;
 		//int r2=fastrand()%testCases.size();
-		int r2=rand()%testCases.size();
+		int r2=(fastrand() + (RAND_MAX * fastrand())) %testCases.size();
 
 		if (j%queries_per_connections==0) {
 			mysql_idx=r1;
diff --git a/test/tap/tests/set_testing-240.h b/test/tap/tests/set_testing-240.h
index 60254da37..68b42f001 100644
--- a/test/tap/tests/set_testing-240.h
+++ b/test/tap/tests/set_testing-240.h
@@ -146,7 +146,7 @@ struct cpu_timer
 
 
 inline int fastrand() {
-	g_seed = (214014*g_seed+2531011);
+	g_seed = (214013*g_seed+2531011);
 	return (g_seed>>16)&0x7FFF;
 }
 

From 13c5ed3f968a40579e5c04a493c0ccf2f69ce8ea Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20Canna=C3=B2?= <rene.cannao@gmail.com>
Date: Mon, 29 Apr 2024 07:15:28 +0000
Subject: [PATCH 3/5] Increase sleep time in kill_connection3-t

---
 test/tap/tests/kill_connection3-t.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/tap/tests/kill_connection3-t.cpp b/test/tap/tests/kill_connection3-t.cpp
index ef28ac6cb..1c023ffb5 100644
--- a/test/tap/tests/kill_connection3-t.cpp
+++ b/test/tap/tests/kill_connection3-t.cpp
@@ -191,7 +191,7 @@ int main(int argc, char** argv) {
 		rc = run_q(proxysql_admin, s.c_str());
 		ok(rc == 0 , "%s" , s.c_str());
 	}
-	sleep(1);
+	sleep(3);
 	for (int i = 0; i < NUM_CONNS ; i++) {
 		MYSQL * mysql = conns[i];
 		int rc = run_q(mysql, "DO 1");

From df0e36e854b5b6996be4c406f3a570409e3306d1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20Canna=C3=B2?= <rene.cannao@gmail.com>
Date: Tue, 30 Apr 2024 21:03:51 +0700
Subject: [PATCH 4/5] Create MySQL_Connection.md

---
 doc/internal/MySQL_Connection.md | 70 ++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)
 create mode 100644 doc/internal/MySQL_Connection.md

diff --git a/doc/internal/MySQL_Connection.md b/doc/internal/MySQL_Connection.md
new file mode 100644
index 000000000..50377d3c2
--- /dev/null
+++ b/doc/internal/MySQL_Connection.md
@@ -0,0 +1,70 @@
+### Flowchart of `MySQL_Connection::async_query()`
+
+This function asynchronously executes a query on the MySQL connection.  
+It handles various states of the asynchronous query execution process and returns appropriate status codes indicating the result of the execution.
+
+Returns an integer status code indicating the result of the query execution:
+- 0: Query execution completed successfully.
+- -1: Query execution failed.
+- 1: Query execution in progress.
+- 2: Processing a multi-statement query, control needs to be transferred to MySQL_Session.
+- 3: In the middle of processing a multi-statement query.
+
+
+```mermaid
+---
+title: MySQL_Connection::async_query()
+---
+flowchart TD
+Assert["assert()"]
+ValidConnection{Valid Connection}
+ValidConnection -- no --> Assert
+IsServerOffline{"IsServerOffline()"}
+ValidConnection -- yes --> IsServerOffline
+IsServerOffline -- yes --> ReturnMinus1
+asyncStateMachine1{async_state_machine}
+asyncStateMachine2{async_state_machine}
+IsServerOffline -- no --> asyncStateMachine1
+asyncStateMachine1 -- ASYNC_QUERY_END --> Return0
+handler["handler()"]
+asyncStateMachine1 --> handler
+handler --> asyncStateMachine2
+asyncStateMachine2 -- ASYNC_QUERY_END --> mysql_error{"mysql_error"}
+asyncStateMachine2 -- ASYNC_STMT_EXECUTE_END --> mysql_error
+asyncStateMachine2 -- ASYNC_STMT_PREPARE_FAILED --> ReturnMinus1
+asyncStateMachine2 -- ASYNC_STMT_PREPARE_SUCCESSFUL --> Return0
+mysql_error -- yes --> ReturnMinus1
+mysql_error -- no --> Return0
+asyncStateMachine2 -- ASYNC_NEXT_RESULT_START --> Return2
+processing_multi_statement{"processing_multi_statement"}
+asyncStateMachine2 --> processing_multi_statement
+processing_multi_statement -- yes --> Return3
+processing_multi_statement -- no --> Return1
+ReturnMinus1["return -1"]
+Return0["return 0"]
+Return1["return 1"]
+Return2["return 2"]
+Return3["return 3"]
+```
+
+### Flowchart of `MySQL_Connection::IsServerOffline()`
+
+```mermaid
+---
+title: MySQL_Connection::IsServerOffline()
+---
+flowchart TD
+True[true]
+False[false]
+SS1{"server_status"}
+SA{"shunned_automatic"}
+SB{"shunned_and_kill_all_connections"}
+SS1 -- OFFLINE_HARD --> True
+SS1 -- REPLICATION_LAG --> True
+SS1 -- SHUNNED --> SA
+SA -- yes --> SB
+SB -- yes --> True
+SA -- no --> False
+SB -- no --> False
+SS1 --> False
+```

From 6c7c0cc2b583ccfff64968d281a2e6fa5b7f5b02 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20Canna=C3=B2?= <rene.cannao@gmail.com>
Date: Tue, 30 Apr 2024 21:48:48 +0700
Subject: [PATCH 5/5] Create MySQL_Session.md

---
 doc/internal/MySQL_Session.md | 68 +++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)
 create mode 100644 doc/internal/MySQL_Session.md

diff --git a/doc/internal/MySQL_Session.md b/doc/internal/MySQL_Session.md
new file mode 100644
index 000000000..e56fc6c29
--- /dev/null
+++ b/doc/internal/MySQL_Session.md
@@ -0,0 +1,68 @@
+### Flowchart of `MySQL_Session::RunQuery()`
+
+This function mostly calls `MySQL_Connection::async_query()` with the right arguments.  
+Returns an integer status code indicating the result of the query execution:
+- 0: Query execution completed successfully.
+- -1: Query execution failed.
+- 1: Query execution in progress.
+- 2: Processing a multi-statement query, control needs to be transferred to MySQL_Session.
+- 3: In the middle of processing a multi-statement query.
+
+```mermaid
+---
+title: MySQL_Session::RunQuery()
+---
+flowchart TD
+RQ["MySQL_Connection::async_query()"]
+BEGIN --> RQ
+RQ --> END
+```
+
+### Flowchart of `MySQL_Session::handler()`
+
+WORK IN PROGRESS
+
+```mermaid
+---
+title: MySQL_Session::handler()
+---
+flowchart TD
+RQ["rc = RunQuery()"]
+RC{rc}
+CBCS["rc1 = handler_ProcessingQueryError_CheckBackendConnectionStatus()"]
+RC1{rc1}
+RQ --> RC
+RC -- 0 --> OK
+RC -- -1 --> CBCS
+CBCS --> RC1
+CS["CONNECTING_SERVER"]
+ReturnMinus1["return -1"]
+RC1 -- -1 --> ReturnMinus1
+RC1 -- 1 --> CS
+HM1CLE1["handler_minus1_ClientLibraryError()"]
+HM1CLE2["handler_minus1_ClientLibraryError()"]
+myerr1{"myerr >= 2000
+&&
+myerr < 3000"}
+RC1 --> myerr1
+myerr1 -- yes --> HM1CLE1
+HM1CLE1 -- true --> CS
+HM1CLE1 -- false --> ReturnMinus1
+HM1LEDQ1["handler_minus1_LogErrorDuringQuery()"]
+myerr1 -- no --> HM1LEDQ1
+HM1HEC1["handler_minus1_HandleErrorCodes()"]
+HM1LEDQ1 --> HM1HEC1
+HM1HEC1 -- true --> HR1{"handler_ret"}
+HR1 -- 0 --> CS
+HR1 --> RHR1["return handler_ret"]
+HM1GEM1["handler_minus1_GenerateErrorMessage()"]
+HM1HEC1 -- false --> HM1GEM1
+RE["RequestEnd()"]
+HM1HBC1["handler_minus1_HandleBackendConnection()"]
+HM1GEM1 --> RE
+RE --> HM1HBC1
+```
+
+
+### Flowchart of `MySQL_Session::handler_ProcessingQueryError_CheckBackendConnectionStatus()`
+TODO