ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/Coro-Mysql/README
(Generate patch)

Comparing Coro-Mysql/README (file contents):
Revision 1.2 by root, Sat May 30 06:58:22 2009 UTC vs.
Revision 1.6 by root, Mon Mar 4 11:40:52 2019 UTC

1NAME 1NAME
2 Coro::Mysql - let other threads run while doing mysql requests 2 Coro::Mysql - let other threads run while doing mysql/mariadb requests
3 3
4SYNOPSIS 4SYNOPSIS
5 use Coro::Mysql; 5 use Coro::Mysql;
6 6
7 my $DBH = Coro::Mysql::unblock DBI->connect (...); 7 my $DBH = Coro::Mysql::unblock DBI->connect (...);
8 8
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 all threads
16 of a process, but only the thread that does the request. It should work
17 for both DBD::mysql and DBD::MariaDB connections and a wide range of
18 mariadb/mysql client libraries.
16 19
17 This can be used to make parallel sql requests using Coro, or to do 20 This can be used to make parallel sql requests using Coro, or to do
18 other stuff while mysql is rumbling in the background. 21 other stuff while mariadb is rumbling in the background.
19 22
20 CAVEAT 23 CAVEAT
21 Note that this module must be linked against exactly the same 24 Note that this module must be linked against exactly the same (shared,
22 libmysqlclient library as DBD::mysql, otherwise it will not work. 25 possibly not working with all OSes) libmariadb/libmysqlclient library as
26 DBD::MariaDB/DBD::mysql, otherwise it will not work.
23 27
24 Also, while this module makes database handles non-blocking, you still 28 Also, while this module makes database handles non-blocking, you still
25 cannot run multiple requests in parallel on the same database handle. If 29 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 30 you want to run multiple queries in parallel, you have to create
27 multiple database connections, one for each thread that runs queries. 31 multiple database connections, one for each thread that runs queries.
32 Not doing so can corrupt your data - use a Coro::Semaphore to protetc
33 access to a shared database handle when in doubt.
28 34
29 If you make sure that you never run two or more requests in parallel, 35 If you make sure that you never run two or more requests in parallel,
30 you cna freely share the database handles between threads, of course. 36 you can freely share the database handles between threads, of course.
31
32 Also, this module uses a number of "unclean" techniques (patching an
33 internal libmysql structure for one thing) and was hacked within a few
34 hours on a long flight to Malaysia.
35
36 It does, however, check whether it indeed got the structure layout
37 correct, so you should expect perl exceptions or early crashes as
38 opposed to data corruption when something goes wrong.
39 37
40 SPEED 38 SPEED
41 This module is implemented in XS, and as long as mysqld replies quickly 39 This module is implemented in XS, and as long as mysqld replies quickly
42 enough, it adds no overhead to the standard libmysql communication 40 enough, it adds no overhead to the standard libmysql communication
43 routines (which are very badly written). 41 routines (which are very badly written, btw.). In fact, since it has a
42 more efficient buffering and allows requests to run in parallel, it
43 often decreases the actual time to run many queries considerably.
44 44
45 For very fast queries ("select 0"), this module can add noticable 45 For very fast queries ("select 0"), this module can add noticable
46 overhead (around 15%) as it tries to switch to other coroutines when 46 overhead (around 15%, 7% when EV can be used) as it tries to switch to
47 mysqld doesn't deliver the data instantly. 47 other coroutines when mysqld doesn't deliver the data immediately,
48 although, again, when running queries in parallel, they will usually
49 execute faster.
48 50
49 For most types of queries, there will be no overhead, especially on 51 For most types of queries, there will be no extra latency, especially on
50 multicore systems where your perl process can do other things while 52 multicore systems where your perl process can do other things while
51 mysqld does its stuff. 53 mysqld does its stuff.
54
55 LIMITATIONS
56 This module only supports "standard" mysql connection handles - this
57 means unix domain or TCP sockets, and excludes SSL/TLS connections,
58 named pipes (windows) and shared memory (also windows). No support for
59 these connection types is planned, either.
60
61CANCELLATION
62 Cancelling a thread that is within a mysql query will likely make the
63 handle unusable. As far as Coro::Mysql is concerned, the handle can be
64 safely destroyed, but it's not clear how mysql itself will react to a
65 cancellation.
66
67FUNCTIONS
68 Coro::Mysql offers these functions, the only one that oyu usually need
69 is "unblock":
52 70
53 $DBH = Coro::Mysql::unblock $DBH 71 $DBH = Coro::Mysql::unblock $DBH
54 This function takes a DBI database handles and "patches" it so it 72 This function takes a DBI database handles and "patches" it so it
55 becomes compatible to Coro threads. 73 becomes compatible to Coro threads.
56 74
57 After that, it returns the patched handle - you should always use 75 After that, it returns the patched handle - you should always use
58 the newly returned database handle. 76 the newly returned database handle.
59 77
78 It is safe to call this function on any database handle (or just
79 about any value), but it will only do anything to DBD::mysql
80 handles, others are returned unchanged. That means it is harmless
81 when applied to database handles of other databases.
82
83 It is also safe to pass "undef", so code like this is works as
84 expected:
85
86 my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
87 or die $DBI::errstr;
88
89 $bool = Coro::Mysql::is_unblocked $DBH
90 Returns true iff the database handle was successfully patched for
91 non-blocking operations.
92
93 $bool = Coro::Mysql::have_ev
94 Returns true if this Coro::Mysql installation is compiled with
95 special support for EV or not.
96
97 Even if compiled in, it will only be used if EV is actually the
98 AnyEvent event backend.
99
100USAGE EXAMPLE
101 This example uses PApp::SQL and Coro::on_enter to implement a function
102 "with_db", that connects to a database, uses "unblock" on the resulting
103 handle and then makes sure that $PApp::SQL::DBH is set to the
104 (per-thread) database handle when the given thread is running (it does
105 not restore any previous value of $PApp::SQL::DBH, however):
106
107 use Coro;
108 use Coro::Mysql;
109 use PApp::SQL;
110
111 sub with_db($$$&) {
112 my ($database, $user, $pass, $cb) = @_;
113
114 my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
115 or die $DBI::errstr;
116
117 Coro::on_enter { $PApp::SQL::DBH = $dbh };
118
119 $cb->();
120 }
121
122 This function makes it possible to easily use PApp::SQL with
123 Coro::Mysql, without worrying about database handles.
124
125 # now start 10 threads doing stuff
126 async {
127
128 with_db "DBI:mysql:test", "", "", sub {
129 sql_exec "update table set col = 5 where id = 7";
130
131 my $st = sql_exec \my ($id, $name),
132 "select id, name from table where name like ?",
133 "a%";
134
135 while ($st->fetch) {
136 ...
137 }
138
139 my $id = sql_insertid sql_exec "insert into table values (1,2,3)";
140 # etc.
141 };
142
143 } for 1..10;
144
145SEE ALSO
146 Coro, PApp::SQL (a user friendly but efficient wrapper around DBI).
147
148HISTORY
149 This module was initially hacked together within a few hours on a long
150 flight to Malaysia, and seems to have worked ever since, with minor
151 adjustments for newer libmysqlclient libraries.
152
153 Well, at least until mariadb introduced the new Pluggable Virtual IO API
154 in mariadb 10.3, which changed and broke everything. On the positive
155 side, the old system was horrible to use, as many GNU/Linux
156 distributions forgot to include the required heaqder files and there
157 were frequent small changes, while the new PVIO system seems to be
158 "official" and hopefully better supported.
159
60AUTHOR 160AUTHOR
61 Marc Lehmann <schmorp@schmorp.de> 161 Marc Lehmann <schmorp@schmorp.de>
62 http://home.schmorp.de/ 162 http://home.schmorp.de/
63 163

Diff Legend

– Removed lines
+ Added lines
< Changed lines
> Changed lines