InnoDB regularly reports pages as being "evicted without access" as below:
Pages read ahead 0.00/s, evicted without access 3.12/s, Random read ahead 0.00/s
This happens, although read_ahead is disabled:
| innodb_random_read_ahead | OFF |
| innodb_read_ahead | none |
| innodb_read_ahead_threshold | 56 |
Upon code analysis I found out that the status counter buf_pool->stat.n_ra_pages_evicted is only incremented in the function call buf_LRU_free_from_common_LRU_list. The relevant part of code is:
buf_LRU_free_from_common_LRU_list(
...
accessed = buf_page_is_accessed(bpage);
freed = buf_LRU_free_block(bpage, TRUE, have_LRU_mutex);
mutex_exit(block_mutex);
if (freed) {
/* Keep track of pages that are evicted without
ever being accessed. This gives us a measure of
the effectiveness of readahead */
if (!accessed) {
++buf_pool->stat.n_ra_pages_evicted;
}
return(TRUE);
}
So the status counter buf_pool->stat.n_ra_pages_evicted can only really be incremented if the access time of the page is not set. While if read_ahead is disabled, then a page will always have access time set, because it would have been accessed to be read into the buffer pool.
Upon discussion with Laurynas there seems to be a discrepancy in how access time for a page is set. May be Laurynas can comment further here.
buf_pool-