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Revision 1.5 by root, Thu Oct 11 03:21:49 2012 UTC

… …
9DESCRIPTION 9DESCRIPTION
10 (Note that in this manual, "thread" refers to real threads as 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 11 implemented by the Coro module, not to the built-in windows process
12 emulation which unfortunately is also called "threads") 12 emulation which unfortunately is also called "threads")
13 13
14 This module "patches" DBD::mysql database handles so that they do not 14 This module replaces the I/O handlers for a database connection, with
15 block the whole process, but only the thread that they are used in. 15 the effect that "patched" database handles no longer block the all
16 threads of a process, but only the thread that does the request.
16 17
17 This can be used to make parallel sql requests using Coro, or to do 18 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 other stuff while mysql is rumbling in the background.
19 20
20 CAVEAT 21 CAVEAT
21 Note that this module must be linked against exactly the same (shared, 22 Note that this module must be linked against exactly the same (shared,
22 possibly not working with all OSes) libmysqlclient library as 23 possibly not working with all OSes) libmysqlclient library as
23 DBD::mysql, otherwise it will not work. 24 DBD::mysql, otherwise it will not work.
24 25
26 Also, this module requires a header file that apparently isn't installed
27 everywhere (violite.h), and therefore comes with it's own copy, which
28 might or might not be compatible to the violite.h of your library - when
29 in doubt, make sure all the libmysqlclient header files are installed
30 and delete the violite.h header that comes with this module.
31
32 On the good side, this module does a multitude of checks to ensure that
33 the libray versions match on the binary level, so on incompatibilities
34 you should expect an exception when trying to unblock a handle, rather
35 than data corruption.
36
25 Also, while this module makes database handles non-blocking, you still 37 Also, while this module makes database handles non-blocking, you still
26 cannot run multiple requests in parallel on the same database handle. If 38 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 39 you want to run multiple queries in parallel, you have to create
28 multiple database connections, one for each thread that runs queries. 40 multiple database connections, one for each thread that runs queries.
29 Not doing so can corrupt your data - use a Coro::Semaphore when in 41 Not doing so can corrupt your data - use a Coro::Semaphore to protetc
30 doubt. 42 access to a shared database handle when in doubt.
31 43
32 If you make sure that you never run two or more requests in parallel, 44 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. 45 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 46
43 SPEED 47 SPEED
44 This module is implemented in XS, and as long as mysqld replies quickly 48 This module is implemented in XS, and as long as mysqld replies quickly
45 enough, it adds no overhead to the standard libmysql communication 49 enough, it adds no overhead to the standard libmysql communication
46 routines (which are very badly written, btw.). In fact, since it has a 50 routines (which are very badly written, btw.). In fact, since it has a
… …
136 } for 1..10; 140 } for 1..10;
137 141
138SEE ALSO 142SEE ALSO
139 Coro, PApp::SQL (a user friendly but efficient wrapper around DBI). 143 Coro, PApp::SQL (a user friendly but efficient wrapper around DBI).
140 144
145HISTORY
146 This module was initially hacked together within a few hours on a long
147 flight to Malaysia, and seems to have worked ever since, with minor
148 adjustments for newer libmysqlclient libraries.
149
141AUTHOR 150AUTHOR
142 Marc Lehmann <schmorp@schmorp.de> 151 Marc Lehmann <schmorp@schmorp.de>
143 http://home.schmorp.de/ 152 http://home.schmorp.de/
144 153

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