[DOC] InnoDB status vars are not conclusive

Innodb_master_thread_active_loops
Innodb_master_thread_idle_loops

InnoDB has a so-called "master" thread which performs background tasks
depending on the server state, once per second. If the server is under
workload, the master thread runs the following: performs background
table drops; performs change buffer merge, adaptively; flushes the
redo log to disk; evicts tables from the dictionary cache if needed to
satisfy its size limit; makes a checkpoint. If the server is idle:
performs background table drops, flushes and/or checkpoints the redo
log if needed due to the checkpoint age; performs change buffer merge
at full I/O capacity; evicts tables from the dictionary cache if
needed; makes a checkpoint; (5.6 only) and purges archived logs if
needed.

These two variables represent the number of times the above one-second
loop was executed for active and idle server states.

Innodb_backgroud_log_sync

The number of times the InnoDB master thread has written and flushed
the redo log.

Innodb_lsn_current

The current log sequence number

Innodb_lsn_flushed

The current maximum LSN that has been written and flushed to disk

Innodb_lsn_last_checkpoint

The LSN of the latest completed checkpoint

Innodb_checkpoint_age

The current InnoDB checkpoint age, i.e. the difference bweteen the
current LSN and the LSN of the last completed checkpoint

Innodb_checkpoint_max_age

The maximum allowed checkppoint age above which the redo log is close
to full and a checkpoint must happen before any further redo log
writes

Innodb_mem_adaptive_hash

The current size, in bytes, of the adaptive hash index.

Innodb_mem_dictionary

The current size, in bytes, of the InnoDB in-memory data dictionary
info

Innodb_mem_total

The total amount of memory, in bytes, InnoDB has allocated in the
process heap memory.

Innodb_buffer_pool_pages_LRU_flushed

The total counter of buffer pool pages which have been fiushed from
the LRU list, i.e. too old pages which had to be flushed in order to
make buffer pool room to read in new data pages.

Innodb_buffer_pool_pages_made_not_young

The number of times a buffer pool page was not marked as accessed
recently in the LRU list because of innodb_old_blocks_time setting.

Innodb_buffer_pool_pages_made_young

The number of times a buffer pool page was moved to the young end of
the LRU list due to its access, to prevent its eviction from the
buffer pool.

Innodb_buffer_pool_pages_old

The total number of buffer pool pages which are considered to be old
according to
https://dev.mysql.com/doc/refman/5.7/en/innodb-performance-midpoint_insertion.html

Innodb_descriptors_memory (only in 5.5 / 5.6)

The current size, in bytes, taken by the descriptor array of the
currently active transactions
(https://www.percona.com/blog/2013/04/12/trx-descriptors-mysql-performance-improvements-in-percona-server-5-5-30-30-2/)

Innodb_read_views_memory (only in 5.5 / 5.6)

The current size, in bytes, taken by all the currently open read views

Innodb_max_trx_id

The next free transaction id number

Innodb_oldest_view_low_limit_trx_id

The highest transaction id, above which the current oldest open read
view does not see any transaction changes. Zero if there is n...

Innodb_checkpoint_target_age

The upper limit for the desired InnoDB checkpoint age, that is, InnoDB
will flush aggressively if this value is approached, in order to avoid
exceeding it. If innodb_checkpoint_age_target system variable is not
set, then it's equal to the maximum async checkpoint age target, which
is maintained internally by the server. If the system variable is set,
then this status variable is the lesser of that target and the system
variable value.

Partial fix: https://github.com/percona/percona-server/pull/1794

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-1604