Laurynas Biveinis added a comment - 2017-06-12 18:38 I believe we have worked out the correct conditions for starting/not starting page cleaners / LRU managers in the latest XtraDB source. Specifically, LRU manager has to be started on innodb_read_only too - it evicts in addition to flushing, and so without it, a --innodb-empty-free-list-algorithm=backoff would starve InnoDB of free pages.

Marko Mäkelä added a comment - 2018-01-22 15:52 I noticed that I had forgotten to update this ticket when I committed the change to MariaDB 10.0.32, 10.1.25. In MariaDB 10.2 there is no buf_flush_lru_manager_thread . laurynas , thank you for the hint. It looks like I should revert this change, or otherwise if innodb_read_only in combination with innodb_empty_free_list_algorithm=backoff may cause the buffer pool to run out. I will construct and run a test case.

Marko Mäkelä added a comment - 2018-01-23 06:21 I tried and failed to reproduce the buffer pool starvation. It turns out that when the buf_flush_lru_manager_thread is not running, buf_LRU_get_free_block() will choose the legacy algorithm: if (srv_empty_free_list_algorithm == SRV_EMPTY_FREE_LIST_BACKOFF && buf_lru_manager_is_active && (srv_shutdown_state == SRV_SHUTDOWN_NONE || srv_shutdown_state == SRV_SHUTDOWN_CLEANUP)) { The condition buf_lru_manager_is_active would not hold, because innobase_start_or_create_for_mysql() will not set the variable unless it is starting the buf_flush_lru_manager_thread . For the record, I used the following test case: --source include/have_innodb.inc --source include/not_embedded.inc   SET GLOBAL innodb_file_per_table= on ; create table t(a char (255),b char (255),c char (255), d char (255) not null unique , primary key (a,b,c))engine=innodb;   begin ; --disable_query_log let $n=30000; while ($n) { eval insert into t values ($n,$n,$n,$n); dec $n; } --enable_query_log commit ; -- let $restart_parameters=--innodb-read-only --innodb-buffer-pool-size=20m --innodb-buffer-pool-instances=1 -- source include/restart_mysqld.inc   check table t; By default, innodb_buffer_pool_instances would be 0, which would be replaced with 8 if the innodb_buffer_pool_size is large enough. It seems that MariaDB has little or no regression test coverage of the innodb_empty_free_list_algorithm=backoff (which is the XtraDB default in 10.0 and 10.1), because the size of a single buffer pool instance would be smaller than 20MiB by default. 1280 pages (20MiB at innodb_page_size=16k ) is the limit that is enforced by innodb_empty_free_list_algorithm_allowed() .

Laurynas Biveinis added a comment - 2018-01-23 07:37 That is correct, I had forgotten about the added && buf_lru_manager_is_active condition.