… with an empty transaction list when creating read views. However, the more general descriptors optimization…left) vs. two-node (on the right) configuration. No surprises here, the general pattern is consistent… cases Percona Server performance is even slightly ahead of MySQL 5.6.10, but nothing …
Post: Can Innodb Read-Ahead reduce read performance ?
June 26, 2007 By 2 Comments
… are 4 read-ahead requests, 64 pages each. What seems to be happening (I’m using “seems” as there are no detailed enough stats available) is once thread has issued read-ahead request it has to wait for… of read-ahead requests. May be it is poor read-ahead performance plus multiple threads doing scattered O_DIRECT (so no OS read-ahead) single page reads which…
Post: Multi Range Read (MRR) in MySQL 5.6 and MariaDB 5.5
March 21, 2012 By 10 Comments
…_buffer_pool_read_ahead 0 20920 23669 20920 23734 Innodb_buffer_pool_read_requests 1361851 1264739 1235472 1263290 1235781 Innodb_buffer_pool_reads 120548…_pool_read_ahead which shows that the access pattern was sequential and hence InnoDB decided to do read_ahead, while in MySQL 5.5 no read_ahead was done because the access pattern was not sequential. Another thing to note is that more read_ahead is done…
Post: read_ahead (disabled) as steroid
May 12, 2009 By 4 Comments
…) on ext3, 32GB of RAM. As you see there almost no difference and you may say what’s the reason in… “read_ahead“. And if in the same benchmark you disable read-ahead (innodb_read_ahead=none), you can see improvement about 15% Actually control of read_ahead is… – in the same time gaps can be smoother with disabled read_ahead, however disabling it does not show such improvement like on…
Comment: InnoDB: look after fragmentation
November 7, 2009 By 12 Comments
… and hence at least 16K worth of data would be read each time. The number of rows of course depends on… rows per page. Now note in the worse case scenario no read-aheads will trigger and all IO will be done by single… be looking at about 3MB/sec read speed which is 30-50 times slower than sequential read speed of the same drive.
Post: MySQL 5.6 vs MySQL 5.5 and the Star Schema Benchmark
March 11, 2013 By 7 Comments
…modified the queries to use ANSI JOIN syntax. No other changes to the queries were made. …READ_AHEAD: 38459 * NUMBER_PAGES_READ_AHEAD: 38457 NUMBER_READ_AHEAD_EVICTED: 0 * NUMBER_READ_AHEAD_EVICTED: 0 READ_AHEAD_RATE: 1240.5728847456533 * READ_AHEAD_RATE: 0 READ_AHEAD_EVICTED_RATE: 0 * READ_AHEAD…
Post: Heikki Tuuri Innodb answers - Part I
October 26, 2007 By 19 Comments
… overwritten in buffer pool by large full table scan HT: No PZ: Another possible area of optimization. I frequently see batch…. Q10: When Innodb decides to schedule sequential read-ahead, random read ahead ? HT: InnoDB schedules a sequential read-ahead when it notices an ascending access pattern…
Post: Is there room for more MySQL IO Optimization?
January 3, 2013 By 11 Comments
…OS = 64-bit Threading | NPTL 2.15 SELinux | No SELinux detected Virtualized | No virtualization detected # Processor ################################################## Processors | physical = 1, cores … may be doing some form of read-ahead on its, making OS read ahead help unneeded. Well there is a …
Post: Heikki Tuuri answers to Innodb questions, Part II
November 4, 2007 By 13 Comments
… one read-ahead can happen at the same time. How many read-aheads can be waiting in Queue when or Innodb will schedule more read-aheads only when given read-ahead is completed? HT…, removing one bottleneck moves the contention to another place. Thus, no general rules can be established. I have assigned Inaam as…
Post: The performance effects of new patches
September 9, 2008 By 14 Comments
…, we will publish them eventually). There are no delays between transactions (no thinking time, no keying time), it uses MySQL C API and… added. innodb_read_ahead (default 3) This controls [enable/disable] of read-ahead. 3: normal 2: enable linear read-ahead only 1: enable random read-ahead only 0…
