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NAME |
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AnyEvent::DBI - asynchronous DBI access |
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|
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SYNOPSIS |
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use AnyEvent::DBI; |
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|
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my $cv = AnyEvent->condvar; |
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|
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my $dbh = new AnyEvent::DBI "DBI:SQLite:dbname=test.db", "", ""; |
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|
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$dbh->exec ("select * from test where num=?", 10, sub { |
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my ($rows, $rv) = @_; |
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|
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print "@$_\n" |
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for @$rows; |
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|
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$cv->broadcast; |
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}); |
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|
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# asynchronously do sth. else here |
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|
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$cv->wait; |
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|
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DESCRIPTION |
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This module is an AnyEvent user, you need to make sure that you use and |
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run a supported event loop. |
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|
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This module implements asynchronous DBI access my forking or executing |
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separate "DBI-Server" processes and sending them requests. |
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|
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It means that you can run DBI requests in parallel to other tasks. |
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|
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The overhead for very simple statements ("select 0") is somewhere around |
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120% to 200% (dual/single core CPU) compared to an explicit |
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prepare_cached/execute/fetchrow_arrayref/finish combination. |
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|
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METHODS |
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$dbh = new AnyEvent::DBI $database, $user, $pass, [key => value]... |
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Returns a database handle for the given database. Each database |
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handle has an associated server process that executes statements in |
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order. If you want to run more than one statement in parallel, you |
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need to create additional database handles. |
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|
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The advantage of this approach is that transactions work as state is |
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preserved. |
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|
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Example: |
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|
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$dbh = new AnyEvent::DBI |
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"DBI:mysql:test;mysql_read_default_file=/root/.my.cnf", "", ""; |
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|
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Additional key-value pairs can be used to adjust behaviour: |
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|
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on_error => $callback->($dbh, $filename, $line, $fatal) |
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When an error occurs, then this callback will be invoked. On |
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entry, $@ is set to the error message. $filename and $line is |
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where the original request was submitted. |
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|
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If the fatal argument is true then the database connection shuts |
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down and your database handle becomes invalid. All of your |
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request callbacks are called without any arguments. |
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|
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If omitted, then "die" will be called on any errors, fatal or |
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not. |
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|
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The $dbh argument is always a weak reference to the |
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AnyEvent::DBI object. |
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|
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on_connect => $callback->($dbh) |
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If you supply an on_connect callback, then this callback will be |
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invoked after the database connection is attempted. If the |
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connection succeeds, $dbh contains a weak reference to the |
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AnyEvent::DBI object. If the connection fails for any reason, no |
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arguments are passed to the callback and $@ contains |
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$DBI::errstr. |
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|
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Regardless of whether on_connect is supplied, connect errors |
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will result in on_error being called. However, if no on_connect |
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callback is supplied, then connection errors are considered |
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fatal. The client will die() and the on_error callback will be |
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called with $fatal true. When on_connect is supplied, connect |
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error are not fatal and AnyEvent::DBI will not die(). You still |
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cannot, however, use the $dbh object you recived from new() to |
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make requests. |
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|
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timeout => seconds |
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If you supply a timeout parameter (floating point number of |
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seconds), then a timer is started any time the DBI handle |
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expects a response from the server. This includes connection |
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setup as well as requests made to the backend. The timeout spans |
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the duration from the moment the first data is written (or |
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queued to be written) until all expected responses are returned, |
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but is postponed for "timeout" seconds each time more data is |
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returned from the server. If the timer ever goes off then a |
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fatal error is generated. If you have an on_error handler |
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installed, then it will be called, otherwise your program will |
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die(). |
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|
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When altering your databases with timeouts it is wise to use |
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transactions. If you quit due to timeout while performing |
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insert, update or schema-altering commands you can end up not |
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knowing if the action was submitted to the database, |
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complicating recovery. |
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|
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Timeout errors are always fatal. |
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|
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Any additional key-value pairs will be rolled into a hash reference |
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and passed as the final argument to the DBI->connect(...) call. For |
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example, to supress errors on STDERR and send them instead to an |
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AnyEvent::Handle you could do: |
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|
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$dbh = new AnyEvent::DBI |
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"DBI:mysql:test;mysql_read_default_file=/root/.my.cnf", "", "", |
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PrintError => 0, |
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on_error => sub { $log_handle->push_write("DBI Error: $@ at $_[1]:$_[2]\n"); } |
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|
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$dbh->on_error ( $cb->($dbh, $filename, $line, $fatal) ); |
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Sets (or clears) the on_error handler. |
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|
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$dbh->on_connect ( $cb->($dbh) ) ; |
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Sets (or clears) the on_connect handler. |
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|
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$dbh->timeout ( $seconds ) ; |
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Sets (or clears) the database timeout. Useful to extend the timeout |
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when you are about to make a really long query. |
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|
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$dbh->exec ("statement", @args, $cb->($dbh, \@rows, \%metadata )) |
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Executes the given SQL statement with placeholders replaced by |
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@args. The statement will be prepared and cached on the server side, |
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so using placeholders is compulsory. |
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|
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The callback will be called with a weakened AnyEvent::DBI object as |
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the first argument and the result of "fetchall_arrayref" as (or |
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"undef" if the statement wasn't a select statement) as the second |
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argument. Third argument is a hash reference holding metadata about |
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the request. Currently, the only key defined is "$metadata-"{rv}> |
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holding the return value of "execute". Additional metadata might be |
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added. |
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|
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If an error occurs and the "on_error" callback returns, then no |
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arguments will be passed and $@ contains the error message. |
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|
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SEE ALSO |
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AnyEvent, DBI. |
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|
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AUTHOR |
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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|
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Adam Rosenstein <adam@redcondor.com> |
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http://www.redcondor.com/ |
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