[ViewVC] Annotation of: cvs/Coro-Mysql/README

NAME
    Coro::Mysql - let other threads run while doing mysql requests

SYNOPSIS
     use Coro::Mysql;

     my $DBH = Coro::Mysql::unblock DBI->connect (...);

DESCRIPTION
    (Note that in this manual, "thread" refers to real threads as
    implemented by the Coro module, not to the built-in windows process
    emulation which unfortunately is also called "threads")

    This module "patches" DBD::mysql database handles so that they do not
    block the whole process, but only the thread that they are used in.

    This can be used to make parallel sql requests using Coro, or to do
    other stuff while mysql is rumbling in the background.

  CAVEAT
    Note that this module must be linked against exactly the same (shared,
    possibly not working with all OSes) libmysqlclient library as
    DBD::mysql, otherwise it will not work.

    Also, while this module makes database handles non-blocking, you still
    cannot run multiple requests in parallel on the same database handle. If
    you want to run multiple queries in parallel, you have to create
    multiple database connections, one for each thread that runs queries.
    Not doing so can corrupt your data - use a Coro::Semaphore when in
    doubt.

    If you make sure that you never run two or more requests in parallel,
    you can freely share the database handles between threads, of course.

    Also, this module uses a number of "unclean" techniques (patching an
    internal libmysql structure for one thing) and was initially hacked
    within a few hours on a long flight to Malaysia.

    It does, however, check whether it indeed got the structure layout
    correct, so you should expect perl exceptions or early crashes as
    opposed to data corruption when something goes wrong during patching.

  SPEED
    This module is implemented in XS, and as long as mysqld replies quickly
    enough, it adds no overhead to the standard libmysql communication
    routines (which are very badly written, btw.). In fact, since it has a
    more efficient buffering and allows requests to run in parallel, it
    often decreases the actual time to run many queries considerably.

    For very fast queries ("select 0"), this module can add noticable
    overhead (around 15%, 7% when EV can be used) as it tries to switch to
    other coroutines when mysqld doesn't deliver the data immediately,
    although, again, when running queries in parallel, they will usually
    execute faster.

    For most types of queries, there will be no extra latency, especially on
    multicore systems where your perl process can do other things while
    mysqld does its stuff.

  LIMITATIONS
    This module only supports "standard" mysql connection handles - this
    means unix domain or TCP sockets, and excludes SSL/TLS connections,
    named pipes (windows) and shared memory (also windows). No support for
    these connection types is planned, either.

CANCELLATION
    Cancelling a thread that is within a mysql query will likely make the
    handle unusable. As far as Coro::Mysql is concerned, the handle can be
    safely destroyed, but it's not clear how mysql itself will react to a
    cancellation.

FUNCTIONS
    Coro::Mysql offers a single user-accessible function:

    $DBH = Coro::Mysql::unblock $DBH
        This function takes a DBI database handles and "patches" it so it
        becomes compatible to Coro threads.

        After that, it returns the patched handle - you should always use
        the newly returned database handle.

        It is safe to call this function on any database handle (or just
        about any value), but it will only do anything to DBD::mysql
        handles, others are returned unchanged. That means it is harmless
        when applied to database handles of other databases.

        It is also safe to pass "undef", so code like this is works as
        expected:

           my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
              or die $DBI::errstr;

USAGE EXAMPLE
    This example uses PApp::SQL and Coro::on_enter to implement a function
    "with_db", that connects to a database, uses "unblock" on the resulting
    handle and then makes sure that $PApp::SQL::DBH is set to the
    (per-thread) database handle when the given thread is running (it does
    not restore any previous value of $PApp::SQL::DBH, however):

       use Coro;
       use Coro::Mysql;
       use PApp::SQL;

       sub with_db($$$&) {
          my ($database, $user, $pass, $cb) = @_;

          my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
             or die $DBI::errstr;

          Coro::on_enter { $PApp::SQL::DBH = $dbh };

          $cb->();
       }

    This function makes it possible to easily use PApp::SQL with
    Coro::Mysql, without worrying about database handles.

       # now start 10 threads doing stuff
       async {

          with_db "DBI:mysql:test", "", "", sub {
             sql_exec "update table set col = 5 where id = 7";

             my $st = sql_exec \my ($id, $name),
                               "select id, name from table where name like ?",
                               "a%";

             while ($st->fetch) {
                ...
             }

             my $id = sql_insertid sql_exec "insert into table values (1,2,3)";
             # etc.
          };

       } for 1..10;

SEE ALSO
    Coro, PApp::SQL (a user friendly but efficient wrapper around DBI).

AUTHOR
     Marc Lehmann <schmorp@schmorp.de>
     http://home.schmorp.de/

Revision:	1.4
Committed:	Sun Feb 20 10:35:10 2011 UTC (13 years, 4 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_1, rel-1_2
Changes since 1.3:	+26 -9 lines
Log Message:	1.1
#	User	Rev	Content
1	root	1.2	NAME
2			Coro::Mysql - let other threads run while doing mysql requests
3
4			SYNOPSIS
5			use Coro::Mysql;
6
7			my $DBH = Coro::Mysql::unblock DBI->connect (...);
8
9			DESCRIPTION
10			(Note that in this manual, "thread" refers to real threads as
11			implemented by the Coro module, not to the built-in windows process
12			emulation which unfortunately is also called "threads")
13
14			This module "patches" DBD::mysql database handles so that they do not
15			block the whole process, but only the thread that they are used in.
16
17			This can be used to make parallel sql requests using Coro, or to do
18			other stuff while mysql is rumbling in the background.
19
20			CAVEAT
21	root	1.4	Note that this module must be linked against exactly the same (shared,
22			possibly not working with all OSes) libmysqlclient library as
23			DBD::mysql, otherwise it will not work.
24	root	1.2
25			Also, while this module makes database handles non-blocking, you still
26			cannot run multiple requests in parallel on the same database handle. If
27			you want to run multiple queries in parallel, you have to create
28			multiple database connections, one for each thread that runs queries.
29	root	1.3	Not doing so can corrupt your data - use a Coro::Semaphore when in
30			doubt.
31	root	1.2
32			If you make sure that you never run two or more requests in parallel,
33	root	1.3	you can freely share the database handles between threads, of course.
34	root	1.2
35			Also, this module uses a number of "unclean" techniques (patching an
36	root	1.4	internal libmysql structure for one thing) and was initially hacked
37			within a few hours on a long flight to Malaysia.
38	root	1.2
39			It does, however, check whether it indeed got the structure layout
40			correct, so you should expect perl exceptions or early crashes as
41	root	1.3	opposed to data corruption when something goes wrong during patching.
42	root	1.2
43			SPEED
44			This module is implemented in XS, and as long as mysqld replies quickly
45			enough, it adds no overhead to the standard libmysql communication
46	root	1.4	routines (which are very badly written, btw.). In fact, since it has a
47			more efficient buffering and allows requests to run in parallel, it
48			often decreases the actual time to run many queries considerably.
49	root	1.2
50			For very fast queries ("select 0"), this module can add noticable
51	root	1.4	overhead (around 15%, 7% when EV can be used) as it tries to switch to
52			other coroutines when mysqld doesn't deliver the data immediately,
53			although, again, when running queries in parallel, they will usually
54			execute faster.
55	root	1.2
56	root	1.4	For most types of queries, there will be no extra latency, especially on
57	root	1.2	multicore systems where your perl process can do other things while
58			mysqld does its stuff.
59
60	root	1.3	LIMITATIONS
61			This module only supports "standard" mysql connection handles - this
62			means unix domain or TCP sockets, and excludes SSL/TLS connections,
63			named pipes (windows) and shared memory (also windows). No support for
64			these connection types is planned, either.
65
66	root	1.4	CANCELLATION
67			Cancelling a thread that is within a mysql query will likely make the
68			handle unusable. As far as Coro::Mysql is concerned, the handle can be
69			safely destroyed, but it's not clear how mysql itself will react to a
70			cancellation.
71
72	root	1.3	FUNCTIONS
73			Coro::Mysql offers a single user-accessible function:
74
75	root	1.2	$DBH = Coro::Mysql::unblock $DBH
76			This function takes a DBI database handles and "patches" it so it
77			becomes compatible to Coro threads.
78
79			After that, it returns the patched handle - you should always use
80			the newly returned database handle.
81
82	root	1.3	It is safe to call this function on any database handle (or just
83			about any value), but it will only do anything to DBD::mysql
84			handles, others are returned unchanged. That means it is harmless
85			when applied to database handles of other databases.
86
87	root	1.4	It is also safe to pass "undef", so code like this is works as
88			expected:
89
90			my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
91			or die $DBI::errstr;
92
93	root	1.3	USAGE EXAMPLE
94			This example uses PApp::SQL and Coro::on_enter to implement a function
95			"with_db", that connects to a database, uses "unblock" on the resulting
96			handle and then makes sure that $PApp::SQL::DBH is set to the
97			(per-thread) database handle when the given thread is running (it does
98			not restore any previous value of $PApp::SQL::DBH, however):
99
100			use Coro;
101			use Coro::Mysql;
102			use PApp::SQL;
103
104			sub with_db($$$&) {
105			my ($database, $user, $pass, $cb) = @_;
106
107	root	1.4	my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
108	root	1.3	or die $DBI::errstr;
109
110			Coro::on_enter { $PApp::SQL::DBH = $dbh };
111
112			$cb->();
113			}
114
115			This function makes it possible to easily use PApp::SQL with
116			Coro::Mysql, without worrying about database handles.
117
118			# now start 10 threads doing stuff
119			async {
120
121			with_db "DBI:mysql:test", "", "", sub {
122			sql_exec "update table set col = 5 where id = 7";
123
124			my $st = sql_exec \my ($id, $name),
125			"select id, name from table where name like ?",
126			"a%";
127
128			while ($st->fetch) {
129			...
130			}
131
132			my $id = sql_insertid sql_exec "insert into table values (1,2,3)";
133			# etc.
134			};
135
136			} for 1..10;
137
138			SEE ALSO
139			Coro, PApp::SQL (a user friendly but efficient wrapper around DBI).
140
141	root	1.2	AUTHOR
142			Marc Lehmann <schmorp@schmorp.de>
143			http://home.schmorp.de/
144