Wednesday Jan 21, 2009

Demonstrating the Features of MySQL Native Driver for PHP, mysqlnd

Support for Persistent Connections

ext/mysqli does not support persistent connections when built with libmysql. However ext/mysqli does support persistent connections when built with mysqlnd. To establish a persistent connection with the MySQL server using ext/mysqli and mysqlnd, prepend the database host with the string "p:" (p stands for persistent) as shown below.


$host="p:localhost";
$port=3306;
$socket="/tmp/mysql.sock";
$user="root";
$password="admin";
$dbname="test";

$cxn = new mysqli($host, $user, $password, $dbname, $port, $socket)
	or die ('Could not connect to the database server' . mysqli_connect_error());

ext/mysql, ext/mysqli and PDO_MySQL support persistent connections when built with mysqlnd.

The new API call mysqli_fetch_all()

mysqlnd extends the ext/mysqli API with one brand new method, mysqli _fetch_all().

mysqli_fetch_all() fetches all result rows and return the result set as an associative array, a numeric array, or both. The method signature is shown below for both procedural as well as object oriented style of programming.

Procedural style:

	mixed mysqli_fetch_all (mysqli_result $result [, int $resulttype])

Object oriented style:

	mixed mysqli_result::fetch_all ([int $resulttype])

where: $result is a result set identifier returned by mysqli_query(), mysqli_store_result() or mysqli_use_result(), and $resulttype is an optional constant indicating what type of array should be produced from the current row data. The possible values for this parameter are the constants MYSQLI_ASSOC, MYSQLI_NUM, or MYSQLI_BOTH. Defaults to MYSQLI_NUM.

Because mysqli_fetch_all() returns all the rows as an array in a single step, it may consume more memory than some of its counterparts like mysqli_fetch_array(). mysqli_fetch_array() returns one row at a time from the result set, hence consumes less memory relative to mysqli_fetch_array(). Besides, if you need to iterate over the result set, you may need a foreach() loop and this approach might be little slower compared to the result set retrieval using mysqli_fetch_array(). Hence consider using mysqli_fetch_all() only in those situations where the fetched result set will be sent to another layer for post processing. If you have to process the fetched result set in the same layer with the help of iterators, then the benefit of using the mysqli_fetch_all() method might be minimal, if there is any.

Statistical Data Collection

mysqlnd collects a lot of statistics which you can use to tune your application. mysqlnd enhances ext/mysqli API with three mysqli_get_XX_stats() methods for easy monitoring and to simplify the bottleneck analysis. For example, using a combination of mysqli_get_XX_stats() methods, one can easily identify a PHP client script that is opening more database connections than it needs or selecting more rows than it consumes.

Accessing Client Statistics:

To access per process client statistics, simply call mysqli_get_client_stats() with no arguments. Similarly to access client statistics per connection, call mysqli_get_connection_stats() with the database connection handle as the argument. Both of these methods return an associated array with the name of the statistic parameter as the key and the corresponding data as the value.

Alternatively per process client statistics can be accessed by calling the phpinfo() method.

The above methods return statistics like bytes_sent, bytes_received to represent the number of bytes sent to and received from the MySQL server, result_set_queries to show the number of queries which generated a result set, buffered_sets, unbuffered_sets to show the number of buffered and unbuffered result sets for the queries generating a result set but not run as a prepared statement. rows_fetched_from_server_normal shows the number of rows that have been fetched from the server using buffered and unbuffered result sets. rows_buffered_from_client_normal shows the number of rows fetched from the server and buffered on the client-side, and rows_skipped_normal shows the number of rows generated by the server but not read from the client.

Accessing Zval Cache Statistics:

mysqlnd collects statistics from its internal zval cache, that you can access by calling mysqli_get_cache_stat() method. This method returns an associative array with the name of the statistic as the key and the corresponding data as the value. The zval cache statistics might be useful to tweak zval cahe related php.ini settings for better performance.

Sample PHP Script Demonstrating mysqlnd's Features

The following sample PHP script demonstrates how to:

  • establish persistent connections
  • use mysqli_fetch_all() to fetch and display the result set
  • access client, connection and zval cache statistics using mysqli_get_client_stats(), mysqli_get_connection_stats() and mysqli_get_cache_stat() methods

The code sample in this tutorial try to retrieve the data from the City table in the MySQL test database. The table structure and the data from the City table are shown below by using the mysql client. MySQL server is running on the default port 3306.


bash# mysql -u root -p
Enter password: admin
Welcome to the MySQL monitor.  Commands end with ; or \\g.
Your MySQL connection id is 5
Server version: 5.1.24-rc-standard Source distribution

Type 'help;' or '\\h' for help. Type '\\c' to clear the buffer.

mysql> USE test;
Database changed

mysql> DESCRIBE City;
+----------+-------------+------+-----+---------+-------+
| Field	   | Type	 | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| CityName | varchar(30) | YES	|	| NULL	|	|
+----------+-------------+------+-----+---------+-------+
1 row in set (0.07 sec)

mysql> SELECT \* FROM City;
+--------------------+
| CityName		|
+--------------------+
| Hyderabad, India   |
| San Francisco, USA |
| Sydney, Australia  |
+--------------------+
3 rows in set (0.17 sec)

The main purpose of the following example is only to illustrate the syntactical use of the new features of mysqlnd. The sample code does not represent any real world scenarios.


bash# cat PHPmysqliClientmysqlnd.php

<?php

	/\* create a persistent connection to the MySQL server \*/
	$cxn = new mysqli("p:localhost", "root", "admin", "test", 3306, "/tmp/mysql.sock")
		or die ('Could not connect to the database server' . mysqli_connect_error());

	$query = "SELECT \* FROM City";
	
	/\* execute the query \*/
	if ($cxn->real_query ($query)) {

		/\* initiate the result set retrieval \*/
		if ($result = $cxn->store_result()) {

			/\* find the number of rows in the result set \*/
			$nrows = $result->num_rows;

			echo "\\nRetrieved $nrows row(s).\\n\\n";
			echo "CityName\\n--------\\n";

			$all_rows = $result->fetch_all(MYSQLI_ASSOC);

			for($i = 0; $i < count($all_rows); $i++) {
				echo $all_rows[$i][CityName] . "\\n";
			}
		}

		/\* close the result set \*/
		$result->close();
	}

	echo "\\n\\nClient Statistics After One Query\\n---------------------------------";
	$client_stats = mysqli_get_client_stats();
	#var_dump($client_stats);
	foreach ($client_stats as $key=>$value) {
		if ($value > 0) {
                       	echo "\\n$key : $value";
		}
	}

	echo "\\n\\nStatistics for Connection #1\\n----------------------------";
	$conn_stats = mysqli_get_connection_stats($cxn);
	#var_dump($conn_stats);
	foreach ($conn_stats as $key=>$value) {
		if ($value > 0) {
                       	echo "\\n$key : $value";
		}
	}

	echo "\\n\\nCache Statistics After One Query\\n--------------------------------";
	$cache_stats = mysqli_get_cache_stats();
	#var_dump($cache_stats);
	foreach ($cache_stats as $key=>$value) {
		if ($value > 0) {
                       	echo "\\n$key : $value";
		}
	}

	echo "\\n\\n=================================\\n\\n";
	echo "\\nEstablishing connection #2 to the MySQL server ..\\n\\n";

	/\* create a non-persistent connection to the MySQL server \*/
	$cxn2 = new mysqli("localhost", "root", "admin", "mysql", 3306, "/tmp/mysql.sock")
		or die ('Could not connect to the database server' . mysqli_connect_error());

	$query = "SELECT Host, User FROM user";

	/\* execute the query \*/
	if ($cxn2->real_query ($query)) {

		/\* initiate the result set retrieval \*/
		if ($result = $cxn2->store_result()) {

			/\* find the number of rows in the result set \*/
			$nrows = $result->num_rows;
			echo "\\nRetrieved $nrows row(s).\\n\\n";

			echo "Host\\t\\tUser\\n----\\t\\t----\\n";

			$all_rows = $result->fetch_all(MYSQLI_ASSOC);

			for($i = 0; $i < count($all_rows); $i++) {
				echo $all_rows[$i][Host] . "\\t" . $all_rows[$i][User] . "\\n";
			}
		}

                /\* close the result set \*/
		$result->close();
	}

	echo "\\n\\nClient Statistics After Two Queries\\n-----------------------------------";
	$client_stats = mysqli_get_client_stats();
	#var_dump($client_stats);
	foreach ($client_stats as $key=>$value) {
		if ($value > 0) {
			echo "\\n$key : $value";
		}
	}

	echo "\\n\\nStatistics for Connection #2\\n----------------------------";
	$conn_stats = mysqli_get_connection_stats($cxn2);
	#var_dump($conn_stats);
	foreach ($conn_stats as $key=>$value) {
		if ($value > 0) {
			echo "\\n$key : $value";
		}
	}

	echo "\\n\\nCache Statistics After Two Queries\\n----------------------------------";
	$cache_stats = mysqli_get_cache_stats();
	#var_dump($cache_stats);
	foreach ($cache_stats as $key=>$value) {
		if ($value > 0) {
			echo "\\n$key : $value";
		}
	}

	echo "\\n";

	//phpinfo();

	/\* close the database connections \*/
	$cxn->close();
	$cxn2->close();

?>

bash# /export/home/php53/bin/php PHPmysqliClientmysqlnd.php

Retrieved 3 row(s).

CityName
--------
Hyderabad, India
San Francisco, USA
Sydney, Australia


Client Statistics After One Query
---------------------------------
bytes_sent : 90
bytes_received : 222
packets_sent : 2
packets_received : 9
protocol_overhead_in : 36
protocol_overhead_out : 8
bytes_received_ok_packet : 11
bytes_received_eof_packet : 9
bytes_received_rset_header_packet : 5
bytes_received_rset_field_meta_packet : 54
bytes_received_rset_row_packet : 70
packets_sent_command : 1
packets_received_ok : 1
packets_received_eof : 1
packets_received_rset_header : 1
packets_received_rset_field_meta : 1
packets_received_rset_row : 4
result_set_queries : 1
buffered_sets : 1
rows_fetched_from_server_normal : 3
rows_buffered_from_client_normal : 3
rows_fetched_from_client_normal_buffered : 3
rows_skipped_normal : 3
copy_on_write_performed : 3
connect_success : 1
active_connections : 1
active_persistent_connections : 1
explicit_free_result : 1
mem_erealloc_count : 1
mem_efree_count : 2
mem_realloc_count : 1
proto_text_fetched_string : 3

Statistics for Connection #1
----------------------------
bytes_sent : 90
bytes_received : 222
packets_sent : 2
packets_received : 9
protocol_overhead_in : 36
protocol_overhead_out : 8
bytes_received_ok_packet : 11
bytes_received_eof_packet : 9
bytes_received_rset_header_packet : 5
bytes_received_rset_field_meta_packet : 54
bytes_received_rset_row_packet : 70
packets_sent_command : 1
packets_received_ok : 1
packets_received_eof : 1
packets_received_rset_header : 1
packets_received_rset_field_meta : 1
packets_received_rset_row : 4
result_set_queries : 1
buffered_sets : 1
rows_fetched_from_server_normal : 3
rows_buffered_from_client_normal : 3
rows_skipped_normal : 3
connect_success : 1
active_connections : 1
active_persistent_connections : 1
explicit_free_result : 1
proto_text_fetched_string : 3

Cache Statistics After One Query
--------------------------------
put_misses : 3
get_hits : 3
size : 2000
free_items : 1997
references : 3

=================================


Establishing connection #2 to the MySQL server ..


Retrieved 5 row(s).

Host		User
----		----
127.0.0.1	root
localhost
localhost	root
unknown
unknown root


Client Statistics After Two Queries
-----------------------------------
bytes_sent : 190
bytes_received : 501
packets_sent : 4
packets_received : 21
protocol_overhead_in : 84
protocol_overhead_out : 16
bytes_received_ok_packet : 22
bytes_received_eof_packet : 18
bytes_received_rset_header_packet : 10
bytes_received_rset_field_meta_packet : 148
bytes_received_rset_row_packet : 157
packets_sent_command : 2
packets_received_ok : 2
packets_received_eof : 2
packets_received_rset_header : 2
packets_received_rset_field_meta : 3
packets_received_rset_row : 10
result_set_queries : 2
buffered_sets : 2
rows_fetched_from_server_normal : 8
rows_buffered_from_client_normal : 8
rows_fetched_from_client_normal_buffered : 8
rows_skipped_normal : 8
copy_on_write_performed : 13
connect_success : 2
active_connections : 2
active_persistent_connections : 1
explicit_free_result : 2
mem_erealloc_count : 1
mem_efree_count : 2
mem_realloc_count : 4
proto_text_fetched_string : 13
Statistics for Connection #2
----------------------------
bytes_sent : 100
bytes_received : 279
packets_sent : 2
packets_received : 12
protocol_overhead_in : 48
protocol_overhead_out : 8
bytes_received_ok_packet : 11
bytes_received_eof_packet : 9
bytes_received_rset_header_packet : 5
bytes_received_rset_field_meta_packet : 94
bytes_received_rset_row_packet : 87
packets_sent_command : 1
packets_received_ok : 1
packets_received_eof : 1
packets_received_rset_header : 1
packets_received_rset_field_meta : 2
packets_received_rset_row : 6
result_set_queries : 1
buffered_sets : 1
rows_fetched_from_server_normal : 5
rows_buffered_from_client_normal : 5
rows_skipped_normal : 5
connect_success : 1
active_connections : 1
explicit_free_result : 1
proto_text_fetched_string : 10

Cache Statistics After Two Queries
----------------------------------
put_misses : 13
get_hits : 13
size : 2000
free_items : 1987
references : 4

Before concluding, be adviced that some of the experimental functions that are available with ext/mysqli and libmysql are not available with ext/mysqli and mysqlnd. eg., mysqli_embedded_\*(), mysqli_\*rpl\*_()

Related Blog Post:
MySQL Native Driver for PHP, mysqlnd

Acknowledgments
Andrey Hristov & Ulf Wendel, Sun-MySQL AB

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