Req #66794 [Com]: dba_fetch() cdb handler implements $skip inefficiently

Edit report at https://bugs.php.net/bug.php?id=66794&edit=1 ID: 66794 Comment by: harsh0sharma14 at gmail dot com Reported by: doug at opendns dot com Summary: dba_fetch() cdb handler implements $skip inefficiently Status: Open Type: Feature/Change Request Package: DBM/DBA related Operating System: Any PHP Version: Irrelevant Block user comment: N Private report: N New Comment: Thanks for sharing..!! Previous Comments: ------------------------------------------------------------------------ [2014-02-28 05:02:30] doug at opendns dot com Clarified bug title ------------------------------------------------------------------------ [2014-02-28 04:58:35] doug at opendns dot com Description: ------------ --- From manual page: http://www.php.net/function.dba-fetch --- This is in reference to this bit of the source, which dates back to 2002, so it's applicable to pretty much any version of php since 4.3: https://github.com/php/php-src/blob/master/ext/dba/dba_cdb.c#L160 When you pass a value for $skip to dba_fetch() when reading a cdb database, it'll do $skip reads to bypass those entries. Since a common use case is to do this in a loop (see script below) to read an indeterminate number of duplicate keys from a database, If there end up being 100 entries, you're actually doing several thousand disk operations. Test script: --------------- <?php // Write a sample cdb to demo on $values = array_fill(0, 100, 'test value'); $cdb = dba_open('test.cdb', 'n', 'cdb'); foreach($values as $value) dba_insert('test key', $value, $cdb); dba_close($cdb); // Now actually show the issue (see attached dtruss link for what's happening) $cdb = dba_open('test.cdb', 'r', 'cdb'); $cdbSkip = 0; while ($result = dba_fetch('test key', $cdbSkip, $cdb)) { $cdbSkip++; } Expected result: ---------------- I'd expect approximately 100 read requests against the cdb from the latter half of the script Actual result: -------------- See this output from dtruss: https://gist.github.com/tabacco/86bd9f4b1fd267a62be2 Note the high number of seek and read operations to fetch 100 rows. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=66794&edit=1