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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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1.7 |
Note that this module must be linked against exactly the same (shared, |
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possibly not working with all OSes) F<libmysqlclient> library as |
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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. Not doing so |
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can corrupt your data - use a Coro::Semaphore when in doubt. |
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If you make sure that you never run two or more requests in parallel, you |
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can freely share the database handles between threads, of course. |
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1.1 |
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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 initially hacked within |
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a few 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 during patching. |
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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, btw.). In fact, since it has a |
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more efficient buffering and allows requests to run in parallel, it often |
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decreases the actual time to run many queries considerably. |
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1.1 |
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For very fast queries ("select 0"), this module can add noticable overhead |
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(around 15%, 7% when EV can be used) as it tries to switch to other |
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coroutines when mysqld doesn't deliver the data immediately, although, |
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again, when running queries in parallel, they will usually execute faster. |
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For most types of queries, there will be no extra latency, 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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=head2 LIMITATIONS |
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This module only supports "standard" mysql connection handles - this |
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means unix domain or TCP sockets, and excludes SSL/TLS connections, named |
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pipes (windows) and shared memory (also windows). No support for these |
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connection types is planned, either. |
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=head1 CANCELLATION |
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Cancelling a thread that is within a mysql query will likely make the |
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handle unusable. As far as Coro::Mysql is concerned, the handle can be |
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safely destroyed, but it's not clear how mysql itself will react to a |
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cancellation. |
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=head1 FUNCTIONS |
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Coro::Mysql offers a single user-accessible function: |
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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 AnyEvent (); |
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use Coro (); |
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use Coro::AnyEvent (); # not necessary with newer Coro versions |
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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 = '1.2'; |
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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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It is safe to call this function on any database handle (or just about any |
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value), but it will only do anything to L<DBD::mysql> handles, others are |
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returned unchanged. That means it is harmless when applied to database |
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handles of other databases. |
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It is also safe to pass C<undef>, so code like this is works as expected: |
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my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock |
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or die $DBI::errstr; |
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=cut |
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sub unblock { |
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my ($DBH) = @_; |
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if ($DBH && $DBH->{Driver}{Name} eq "mysql") { |
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my $sock = $DBH->{sock}; |
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open my $fh, "+>&" . $DBH->{sockfd} |
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or croak "Coro::Mysql unable to clone mysql fd"; |
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if (AnyEvent::detect ne "AnyEvent::Impl::EV" || !_use_ev) { |
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require Coro::Handle; |
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$fh = Coro::Handle::unblock ($fh); |
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} |
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_patch $sock, $DBH->{sockfd}, $DBH->{mysql_clientversion}, $fh, tied ${$fh}; |
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} |
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$DBH |
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} |
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1; |
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=back |
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1.4 |
=head1 USAGE EXAMPLE |
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This example uses L<PApp::SQL> and L<Coro::on_enter> to implement a |
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function C<with_db>, that connects to a database, uses C<unblock> on the |
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resulting handle and then makes sure that C<$PApp::SQL::DBH> is set to the |
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(per-thread) database handle when the given thread is running (it does not |
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restore any previous value of $PApp::SQL::DBH, however): |
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use Coro; |
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use Coro::Mysql; |
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use PApp::SQL; |
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sub with_db($$$&) { |
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my ($database, $user, $pass, $cb) = @_; |
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my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock |
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or die $DBI::errstr; |
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Coro::on_enter { $PApp::SQL::DBH = $dbh }; |
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$cb->(); |
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} |
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This function makes it possible to easily use L<PApp::SQL> with |
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L<Coro::Mysql>, without worrying about database handles. |
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# now start 10 threads doing stuff |
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async { |
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with_db "DBI:mysql:test", "", "", sub { |
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sql_exec "update table set col = 5 where id = 7"; |
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my $st = sql_exec \my ($id, $name), |
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"select id, name from table where name like ?", |
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"a%"; |
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while ($st->fetch) { |
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... |
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} |
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my $id = sql_insertid sql_exec "insert into table values (1,2,3)"; |
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# etc. |
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}; |
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} for 1..10; |
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=head1 SEE ALSO |
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L<Coro>, L<PApp::SQL> (a user friendly but efficient wrapper around DBI). |
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1.1 |
=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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