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=head1 NAME |
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Coro::Mysql - let other threads run while doing mysql requests |
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=head1 SYNOPSIS |
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use Coro::Mysql; |
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my $DBH = Coro::Mysql::unblock DBI->connect (...); |
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=head1 DESCRIPTION |
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(Note that in this manual, "thread" refers to real threads as implemented |
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by the Coro module, not to the built-in windows process emulation which |
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unfortunately is also called "threads") |
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This module "patches" DBD::mysql database handles so that they do not |
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block the whole process, but only the thread that they are used in. |
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This can be used to make parallel sql requests using Coro, or to do other |
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stuff while mysql is rumbling in the background. |
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=head2 CAVEAT |
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Note that this module must be linked against exactly the same |
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F<libmysqlclient> library as DBD::mysql, otherwise it will not work. |
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Also, while this module makes database handles non-blocking, you still |
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cannot run multiple requests in parallel on the same database handle. If |
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you want to run multiple queries in parallel, you have to create multiple |
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database connections, one for each thread that runs queries. |
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If you make sure that you never run two or more requests in parallel, you |
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cna freely share the database handles between threads, of course. |
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Also, this module uses a number of "unclean" techniques (patching an |
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internal libmysql structure for one thing) and was hacked within a few |
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hours on a long flight to Malaysia. |
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It does, however, check whether it indeed got the structure layout |
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correct, so you should expect perl exceptions or early crashes as opposed |
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to data corruption when something goes wrong. |
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=head2 SPEED |
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This module is implemented in XS, and as long as mysqld replies quickly |
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enough, it adds no overhead to the standard libmysql communication |
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routines (which are very badly written). |
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For very fast queries ("select 0"), this module can add noticable overhead |
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(around 15%) as it tries to switch to other coroutines when mysqld doesn't |
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deliver the data instantly. |
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For most types of queries, there will be no overhead, especially on |
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multicore systems where your perl process can do other things while mysqld |
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does its stuff. |
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=over 4 |
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=cut |
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package Coro::Mysql; |
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use strict qw(vars subs); |
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no warnings; |
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use Scalar::Util (); |
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use Carp qw(croak); |
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use Guard; |
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use Coro::Handle (); |
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# we need this extra indirection, as Coro doesn't support |
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# calling SLF-like functions via call_sv. |
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sub readable { &Coro::Handle::FH::readable } |
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sub writable { &Coro::Handle::FH::writable } |
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BEGIN { |
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our $VERSION = '0.01'; |
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require XSLoader; |
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XSLoader::load Coro::Mysql::, $VERSION; |
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} |
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=item $DBH = Coro::Mysql::unblock $DBH |
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This function takes a DBI database handles and "patches" it |
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so it becomes compatible to Coro threads. |
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After that, it returns the patched handle - you should always use the |
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newly returned database handle. |
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=cut |
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sub unblock { |
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my ($DBH) = @_; |
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my $sock = $DBH->{sock}; |
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open my $fh, "+>&" . $DBH->{sockfd} |
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or croak "Coro::Mysql unable to clone mysql fd"; |
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$fh = Coro::Handle::unblock $fh; |
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_patch $sock, $DBH->{sockfd}, tied ${$fh}; |
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$DBH->{private_Coro_Mysql} = guard { |
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_unpatch $sock; |
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undef $fh; |
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}; |
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$DBH |
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} |
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1; |
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=back |
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=head1 AUTHOR |
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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=cut |
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