[ViewVC] Contents 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
#	Content
1	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	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
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	Not doing so can corrupt your data - use a Coro::Semaphore when in
30	doubt.
31
32	If you make sure that you never run two or more requests in parallel,
33	you can freely share the database handles between threads, of course.
34
35	Also, this module uses a number of "unclean" techniques (patching an
36	internal libmysql structure for one thing) and was initially hacked
37	within a few hours on a long flight to Malaysia.
38
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	opposed to data corruption when something goes wrong during patching.
42
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	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
50	For very fast queries ("select 0"), this module can add noticable
51	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
56	For most types of queries, there will be no extra latency, especially on
57	multicore systems where your perl process can do other things while
58	mysqld does its stuff.
59
60	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	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	FUNCTIONS
73	Coro::Mysql offers a single user-accessible function:
74
75	$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	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	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	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	my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
108	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	AUTHOR
142	Marc Lehmann <schmorp@schmorp.de>
143	http://home.schmorp.de/
144