[Backport 2.8][#7809][YSQL] Add session flag to enable non-transactio…

…nal writes on COPY

Summary:
Allowing faster writes on copy command by using session variable "yb_force_non_transactional_writes".
The default value for this flag is false.
To enable the flag,
```
SET yb_force_non_transactional_writes=true
```
To disable the flag,
```
SET yb_force_non_transactional_writes=false
```
Note, the session variable must be applied on non-DDL operations as non-transactional writes on DDL operations is not supported.

Test Plan: Jenkins: rebase: 2.8

Reviewers: mihnea, smishra

Reviewed By: smishra

Subscribers: yql, smishra

Differential Revision: https://phabricator.dev.yugabyte.com/D14195

java/yb-pgsql/src/test/java/org/yb/pgsql/TestBatchCopyFrom.java

@@ -47,6 +47,8 @@ public class TestBatchCopyFrom extends BasePgSQLTest {
   private static final String BATCH_TXN_SESSION_VARIABLE_NAME =
       "yb_default_copy_from_rows_per_transaction";
   private static final int BATCH_TXN_SESSION_VARIABLE_DEFAULT_ROWS = 1000;
+  private static final String NON_TXN_WRITE_SESSION_VARIABLE_NAME =
+      "yb_force_non_transactional_writes";
 
   private String getAbsFilePath(String fileName) {
     return TestUtils.getBaseTmpDir() + "/" + fileName;
@@ -440,7 +442,7 @@ public void tesStdinCopyInTransactionBlockWithProceedingTransaction() throws Exc
   }
 
   @Test
-  public void testSessionVariable() throws Exception {
+  public void testBatchTxnSessionVariable() throws Exception {
     String absFilePath = getAbsFilePath("batch-copyfrom-sessionvar.txt");
     String tableName = "batchSessionTable";
     int totalValidLines = 7;
@@ -482,6 +484,37 @@ public void testSessionVariable() throws Exception {
     }
   }
 
+  @Test
+  public void testNonTxnWriteSessionVariable() throws Exception {
+    String absFilePath = getAbsFilePath("batch-copyfrom-nontxn-sessionvar.txt");
+    String tableName = "nontxnSessionVarTable";
+    int totalValidLines = 5;
+    int expectedCopiedLines = totalValidLines;
+
+    createFileInTmpDir(absFilePath, totalValidLines);
+
+    try (Statement statement = connection.createStatement()) {
+      // ensure non-txn session variable is off by default
+      assertOneRow(statement, "SHOW " + NON_TXN_WRITE_SESSION_VARIABLE_NAME, "off");
+      // set non-txn session variable
+      statement.execute("SET " + NON_TXN_WRITE_SESSION_VARIABLE_NAME + "=true");
+      statement.execute(String.format(
+          "CREATE TABLE %s (a Integer, b serial, c varchar, d int)", tableName));
+      statement.execute(String.format(
+          "COPY %s FROM \'%s\' WITH (FORMAT CSV, HEADER)", tableName, absFilePath));
+
+      // ensure no discrepency in result
+      assertOneRow(statement, "SELECT COUNT(*) FROM " + tableName, expectedCopiedLines);
+      // ensure DDL's, DML's execute without error
+      statement.execute("ALTER TABLE " + tableName + " ADD COLUMN e INT");
+      statement.execute("ALTER TABLE " + tableName + " DROP COLUMN e");
+      statement.execute("INSERT INTO " + tableName + " VALUES (100)");
+      statement.execute("TRUNCATE TABLE " + tableName);
+      statement.execute("DROP TABLE " + tableName);
+      statement.execute("CREATE TABLE " + tableName + " (a int primary key, b text)");
+    }
+  }
+
   @Test
   public void testSessionVariableWithRowsPerTransactionOption() throws Exception {
     String absFilePath = getAbsFilePath("batch-copyfrom-sessionvar-with-query-option.txt");

src/postgres/src/backend/executor/ybcModifyTable.c

@@ -55,6 +55,8 @@
 #include "pg_yb_utils.h"
 #include "access/yb_scan.h"
 
+bool yb_force_non_transactional_writes = false;
+
 /*
  * Hack to ensure that the next CommandCounterIncrement() will call
  * CommandEndInvalidationMessages(). The result of this call is not
@@ -417,11 +419,12 @@ Oid YBCExecuteInsertForDb(Oid dboid,
                           TupleDesc tupleDesc,
                           HeapTuple tuple)
 {
+	bool non_transactional = !IsSystemRelation(rel) && yb_force_non_transactional_writes;
 	return YBCExecuteInsertInternal(dboid,
 	                                rel,
 	                                tupleDesc,
 	                                tuple,
-	                                false /* is_single_row_txn */);
+	                                non_transactional);
 }
 
 Oid YBCExecuteNonTxnInsert(Relation rel,

src/postgres/src/backend/utils/misc/guc.c

@@ -42,6 +42,7 @@
 #include "commands/vacuum.h"
 #include "commands/variable.h"
 #include "commands/trigger.h"
+#include "executor/ybcModifyTable.h"
 #include "funcapi.h"
 #include "jit/jit.h"
 #include "libpq/auth.h"
@@ -2008,6 +2009,16 @@ static struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"yb_force_non_transactional_writes", PGC_USERSET, CLIENT_CONN_STATEMENT,
+			gettext_noop("Sets the boolean flag to enable or disable non transaction writes."),
+			NULL
+		},
+		&yb_force_non_transactional_writes,
+		false,
+		NULL, NULL, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, false, NULL, NULL, NULL

src/postgres/src/include/executor/ybcModifyTable.h

@@ -26,6 +26,13 @@
 #include "nodes/execnodes.h"
 #include "executor/tuptable.h"
 
+/**
+ * YSQL guc variables that can be used to enable non transactional writes.
+ * e.g. 'SET yb_force_non_transactional_writes=true'
+ * See also the corresponding entries in guc.c.
+ */
+extern bool yb_force_non_transactional_writes;
+
 //------------------------------------------------------------------------------
 // YugaByte modify table API.