MDEV-30825 innodb_compression_algorithm=0 (none) increments Innodb_num_pages_page_compression_error

fil_page_compress_low returns 0 for both innodb_compression_algorithm=0
and where there is compression errors. On the two callers to this
function, don't increment the compression errors if the algorithm was
none.

Reviewed by: Marko Mäkelä

mysql-test/suite/innodb/r/innodb-page_compression_none.result

+#
+# MDEV-30825 innodb_compression_algorithm=0 (none) increments Innodb_num_pages_page_compression_error
+#
+SET @save_compression_algorithm=@@GLOBAL.innodb_compression_algorithm;
+SET GLOBAL innodb_compression_algorithm=0;
+SELECT VARIABLE_VALUE INTO @compress_errors FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME = 'Innodb_num_pages_page_compression_error';
+CREATE TABLE t (c INT) page_compressed=1 page_compression_level=4 ENGINE=InnoDB;
+INSERT INTO t VALUES (1);
+FLUSH TABLES t FOR EXPORT;
+UNLOCK TABLES;
+SELECT VARIABLE_VALUE - @compress_errors AS NUMBER_OF_ERRORS FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME = 'Innodb_num_pages_page_compression_error';
+NUMBER_OF_ERRORS
+0
+DROP TABLE t;
+SET GLOBAL innodb_compression_algorithm=@save_compression_algorithm;
+#
+# End of 10.4 tests
+#

mysql-test/suite/innodb/t/innodb-page_compression_none.test

+-- source include/innodb_checksum_algorithm.inc
+
+--echo #
+--echo # MDEV-30825 innodb_compression_algorithm=0 (none) increments Innodb_num_pages_page_compression_error
+--echo #
+
+SET @save_compression_algorithm=@@GLOBAL.innodb_compression_algorithm;
+SET GLOBAL innodb_compression_algorithm=0;
+SELECT VARIABLE_VALUE INTO @compress_errors FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME = 'Innodb_num_pages_page_compression_error';
+
+
+CREATE TABLE t (c INT) page_compressed=1 page_compression_level=4 ENGINE=InnoDB;
+INSERT INTO t VALUES (1);
+
+FLUSH TABLES t FOR EXPORT;
+UNLOCK TABLES;
+
+SELECT VARIABLE_VALUE - @compress_errors AS NUMBER_OF_ERRORS FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME = 'Innodb_num_pages_page_compression_error';
+
+DROP TABLE t;
+SET GLOBAL innodb_compression_algorithm=@save_compression_algorithm;
+
+--echo #
+--echo # End of 10.4 tests
+--echo #
+

storage/innobase/fil/fil0pagecompress.cc

@@ -201,6 +201,7 @@ static ulint fil_page_compress_for_full_crc32(
 	bool		encrypted)
 {
 	ulint comp_level = fsp_flags_get_page_compression_level(flags);
+	ulint comp_algo = fil_space_t::get_compression_algo(flags);
 
 	if (comp_level == 0) {
 		comp_level = page_zip_level;
@@ -209,12 +210,12 @@ static ulint fil_page_compress_for_full_crc32(
 	const ulint header_len = FIL_PAGE_COMP_ALGO;
 
 	ulint write_size = fil_page_compress_low(
-		buf, out_buf, header_len,
-		fil_space_t::get_compression_algo(flags), comp_level);
+		buf, out_buf, header_len, comp_algo, comp_level);
 
 	if (write_size == 0) {
 fail:
-		srv_stats.pages_page_compression_error.inc();
+		if (comp_algo != PAGE_UNCOMPRESSED)
+			srv_stats.pages_page_compression_error.inc();
 		return 0;
 	}
 
@@ -293,7 +294,8 @@ static ulint fil_page_compress_for_non_full_crc32(
 				header_len, comp_algo, comp_level);
 
 	if (write_size == 0) {
-		srv_stats.pages_page_compression_error.inc();
+		if (comp_algo != PAGE_UNCOMPRESSED)
+			srv_stats.pages_page_compression_error.inc();
 		return 0;
 	}