[#14009] docdb: fix disable_checksums option in yb_backup

Summary:
c8ce4bd seems to have broken the `--disable_checksums`
option of `yb_backup.py`.  There's an assert in `create_checksum_cmd_not_quoted` that checks that
`self.use_xxhash_checksum` is not `None`. This function is unconditionally called in
`prepare_download_command`. However we do not set `self.use_xxhash_checksum` under all circumstances
when `disable_checksums` is `True`.

Test Plan: Added test.

Reviewers: skedia, oleg, msun

Reviewed By: msun

Subscribers: jenkins-bot, yugaware, slingam, ybase, bogdan

Differential Revision: https://phabricator.dev.yugabyte.com/D19540

ent/src/yb/tools/yb-backup-test_ent.cc

@@ -2456,5 +2456,34 @@ TEST_F(YBBackupTest, YB_DISABLE_TEST_IN_SANITIZERS_OR_MAC(TestColocationDuplicat
   LOG(INFO) << "Test finished: " << CURRENT_TEST_CASE_AND_TEST_NAME_STR();
 }
 
+TEST_F(YBBackupTest, YB_DISABLE_TEST_IN_SANITIZERS_OR_MAC(TestBackupChecksumsDisabled)) {
+  ASSERT_NO_FATALS(CreateTable("CREATE TABLE mytbl (k INT PRIMARY KEY, v TEXT)"));
+  ASSERT_NO_FATALS(InsertOneRow("INSERT INTO mytbl (k, v) VALUES (100, 'foo')"));
+  ASSERT_NO_FATALS(InsertOneRow("INSERT INTO mytbl (k, v) VALUES (101, 'bar')"));
+  ASSERT_NO_FATALS(InsertOneRow("INSERT INTO mytbl (k, v) VALUES (102, 'cab')"));
+
+  const string backup_dir = GetTempDir("backup");
+  ASSERT_OK(RunBackupCommand(
+      {"--backup_location", backup_dir, "--keyspace", "ysql.yugabyte", "--disable_checksums",
+       "create"}));
+  ASSERT_NO_FATALS(InsertOneRow("INSERT INTO mytbl (k, v) VALUES (999, 'foo')"));
+  ASSERT_OK(RunBackupCommand(
+      {"--backup_location", backup_dir, "--keyspace", "ysql.yugabyte_new", "--disable_checksums",
+       "restore"}));
+
+  SetDbName("yugabyte_new");  // Connecting to the second DB from the moment.
+  ASSERT_NO_FATALS(RunPsqlCommand(
+      "SELECT k, v FROM mytbl ORDER BY k",
+      R"#(
+          k  |  v
+        -----+-----
+         100 | foo
+         101 | bar
+         102 | cab
+        (3 rows)
+      )#"));
+  LOG(INFO) << "Test finished: " << CURRENT_TEST_CASE_AND_TEST_NAME_STR();
+}
+
 }  // namespace tools
 }  // namespace yb

managed/devops/bin/yb_backup.py

@@ -1392,6 +1392,9 @@ def post_process_arguments(self):
             XXH64HASH_TOOL_PATH = '/usr/bin/xxhsum'
             SHA_TOOL_PATH = '/usr/bin/shasum'
 
+        if self.args.disable_checksums:
+            self.use_xxhash_checksum = False
+
     def table_names_str(self, delimeter='.', space=' '):
         return get_table_names_str(self.args.keyspace, self.args.table, delimeter, space)