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Revision 1.3 by root, Sat Jul 18 05:58:27 2009 UTC vs.
Revision 1.4 by root, Sun Feb 20 10:35:10 2011 UTC

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16 16
17 This can be used to make parallel sql requests using Coro, or to do 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. 18 other stuff while mysql is rumbling in the background.
19 19
20 CAVEAT 20 CAVEAT
21 Note that this module must be linked against exactly the same 21 Note that this module must be linked against exactly the same (shared,
22 possibly not working with all OSes) libmysqlclient library as
22 libmysqlclient library as DBD::mysql, otherwise it will not work. 23 DBD::mysql, otherwise it will not work.
23 24
24 Also, while this module makes database handles non-blocking, you still 25 Also, while this module makes database handles non-blocking, you still
25 cannot run multiple requests in parallel on the same database handle. If 26 cannot run multiple requests in parallel on the same database handle. If
26 you want to run multiple queries in parallel, you have to create 27 you want to run multiple queries in parallel, you have to create
27 multiple database connections, one for each thread that runs queries. 28 multiple database connections, one for each thread that runs queries.
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30 31
31 If you make sure that you never run two or more requests in parallel, 32 If you make sure that you never run two or more requests in parallel,
32 you can freely share the database handles between threads, of course. 33 you can freely share the database handles between threads, of course.
33 34
34 Also, this module uses a number of "unclean" techniques (patching an 35 Also, this module uses a number of "unclean" techniques (patching an
35 internal libmysql structure for one thing) and was hacked within a few 36 internal libmysql structure for one thing) and was initially hacked
36 hours on a long flight to Malaysia. 37 within a few hours on a long flight to Malaysia.
37 38
38 It does, however, check whether it indeed got the structure layout 39 It does, however, check whether it indeed got the structure layout
39 correct, so you should expect perl exceptions or early crashes as 40 correct, so you should expect perl exceptions or early crashes as
40 opposed to data corruption when something goes wrong during patching. 41 opposed to data corruption when something goes wrong during patching.
41 42
42 SPEED 43 SPEED
43 This module is implemented in XS, and as long as mysqld replies quickly 44 This module is implemented in XS, and as long as mysqld replies quickly
44 enough, it adds no overhead to the standard libmysql communication 45 enough, it adds no overhead to the standard libmysql communication
45 routines (which are very badly written, btw.). 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.
46 49
47 For very fast queries ("select 0"), this module can add noticable 50 For very fast queries ("select 0"), this module can add noticable
48 overhead (around 15%) as it tries to switch to other coroutines when 51 overhead (around 15%, 7% when EV can be used) as it tries to switch to
49 mysqld doesn't deliver the data instantly. 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.
50 55
51 For most types of queries, there will be no overhead, especially on 56 For most types of queries, there will be no extra latency, especially on
52 multicore systems where your perl process can do other things while 57 multicore systems where your perl process can do other things while
53 mysqld does its stuff. 58 mysqld does its stuff.
54 59
55 LIMITATIONS 60 LIMITATIONS
56 This module only supports "standard" mysql connection handles - this 61 This module only supports "standard" mysql connection handles - this
57 means unix domain or TCP sockets, and excludes SSL/TLS connections, 62 means unix domain or TCP sockets, and excludes SSL/TLS connections,
58 named pipes (windows) and shared memory (also windows). No support for 63 named pipes (windows) and shared memory (also windows). No support for
59 these connection types is planned, either. 64 these connection types is planned, either.
65
66CANCELLATION
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.
60 71
61FUNCTIONS 72FUNCTIONS
62 Coro::Mysql offers a single user-accessible function: 73 Coro::Mysql offers a single user-accessible function:
63 74
64 $DBH = Coro::Mysql::unblock $DBH 75 $DBH = Coro::Mysql::unblock $DBH
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71 It is safe to call this function on any database handle (or just 82 It is safe to call this function on any database handle (or just
72 about any value), but it will only do anything to DBD::mysql 83 about any value), but it will only do anything to DBD::mysql
73 handles, others are returned unchanged. That means it is harmless 84 handles, others are returned unchanged. That means it is harmless
74 when applied to database handles of other databases. 85 when applied to database handles of other databases.
75 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
76USAGE EXAMPLE 93USAGE EXAMPLE
77 This example uses PApp::SQL and Coro::on_enter to implement a function 94 This example uses PApp::SQL and Coro::on_enter to implement a function
78 "with_db", that connects to a database, uses "unblock" on the resulting 95 "with_db", that connects to a database, uses "unblock" on the resulting
79 handle and then makes sure that $PApp::SQL::DBH is set to the 96 handle and then makes sure that $PApp::SQL::DBH is set to the
80 (per-thread) database handle when the given thread is running (it does 97 (per-thread) database handle when the given thread is running (it does
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85 use PApp::SQL; 102 use PApp::SQL;
86 103
87 sub with_db($$$&) { 104 sub with_db($$$&) {
88 my ($database, $user, $pass, $cb) = @_; 105 my ($database, $user, $pass, $cb) = @_;
89 106
90 my $dbh = Coro::Mysql::unblock DBI->connect ($database, $user, $pass) 107 my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
91 or die $DBI::errstr; 108 or die $DBI::errstr;
92 109
93 Coro::on_enter { $PApp::SQL::DBH = $dbh }; 110 Coro::on_enter { $PApp::SQL::DBH = $dbh };
94 111
95 $cb->(); 112 $cb->();

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