Handler_read_rnd_next

[AlexJ]

What causes Handler_read_rnd_next to be so high? I am using Xcache with MySQL.

Handler_read_rnd_next 259 M

Handler_read_rnd 1,611 k

Created_tmp_disk_tables 108 k

Qcache_lowmem_prunes 4,393

Opened_tables 4,239

Table_locks_waited 5,799

[AlexJ]

Does high Handler_read_rnd_next 259 M indicates indexes are not properly used or is something is wrong at my end?

[altenerg]

did you delve more into this?

[p4guru]

it's just a counter for when next row in a table is read, it doesn't necessarily mean lack of indexes as per the definition from http://dev.mysql.com...r_read_rnd_next as it could also be due to some queries which mysql query optimizer deems isn't suited to using an index

The number of requests to read the next row in the data file. This value is high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.

if you have a large number of rows in a table i.e. post table, then handler_read_rnd_next can increment alot per query as you are returning more data/rows

if after you have analysed your slow query log and make sure you have properly indexes where needed and if you aren't having mysql related performance issues, it's okay to ignore the high counter value for handler_read_rnd_next

i.e. on one server i manage no db issues at all

mysqladmin ext | grep Handler_read_rnd_next

| Handler_read_rnd_next					| 651021183809  |

[altenerg]

Yea I didn't worry about it since I have zero slow queries (2 seconds) in my logs. Also, the no indexes queries all have "query time = 0". I was just curious after seeing red for Handler_read_rnd and Handler_read_rnd_next in PHPmyAdmin status page.