[#MDEV-4682] QUERY CACHE - add STATISTICS per query and show this informations in qc

Change sql_cache.cc and sql_cache.h to add hit rates and statistics
usable with qc_info plugin

Statistics:
total hits / total time expent in query cache
hits in three categories:
1) low period category: period between the last hit and the current hit < query expent time
2) high period category: period < query expent time * 10 and > query expent time
3) outlier category: period > 1 second, and period > query expent time * 10
3.1) in a future version instead of * 10, we could use number of competitors (concurrent) when inserting this query at query cache
for example if we have 9 concurrent inserts of the same query at query cache this number *10 is an acceptable value for high period, if we have n concurrent inserts a (n+1) value is acceptable

These categories helps to understand what kind of query we have cached:
1) low period hits: in this case if we lose this query entry, we will have a performace problem, and users will tell "the server is slow now"
2) high period hits: we have a query that is executed with a good frequency, removing it we will have a higher i/o in disks
3) outlier period hits: this query isn't a query that we should cache, or we can loose it and we don't see users reporting "hey the server is slow, or the disks is spinning a lot"

this allow a better query cache control (MDEV-4584) and a better cache hit rate when optimizing queries with SQL_CACHE/SQL_NO_CACHE

—
a second part could be an variable (query_cache_stats=0/1) to turn off/on the statistics and use a block memory just to statistics instead of one big block sharing memory with queries flags

in this case:
turn on -> off, should clean this stats memory block
turn off -> on, should create stats with 0 value (maybe a problem with lock contention), or clean all query cache and start from zero

changing query cache queries (invalidate, table invalidate, reallocation, etc) should handle the stats block too

QUERY_CACHE_ID	STATEMENT_SCHEMA	STATEMENT_TEXT	RESULT_FOUND_ROWS	QUERY_ROWS	SELECT_ROWS_READ	QUERY_HITS	QUERY_HITS_PERIOD_LOW	QUERY_HITS_PERIOD_HIGH	QUERY_HITS_PERIOD_OUTLIERS	QUERY_HITS_TOTAL_TIME_US	QUERY_HITS_MEAN_PERIOD_US	QUERY_HITS_MEAN_PERIOD_LOW_US	QUERY_HITS_MEAN_PERIOD_HIGH_US	QUERY_INSERT_TIME	QUERY_LAST_HIT_TIME	SELECT_EXPEND_TIME_US	SELECT_LOCK_TIME_US	TABLES_TYPE	RESULT_LENGTH	RESULT_BLOCKS_COUNT	RESULT_BLOCKS_SIZE	RESULT_BLOCKS_SIZE_USED	FLAGS_CLIENT_LONG_FLAG	FLAGS_CLIENT_PROTOCOL_41	FLAGS_PROTOCOL_TYPE	FLAGS_MORE_RESULTS_EXISTS	FLAGS_IN_TRANS	FLAGS_AUTOCOMMIT	FLAGS_PKT_NR	FLAGS_CHARACTER_SET_CLIENT	FLAGS_CHARACTER_SET_RESULTS	FLAGS_COLLATION_CONNECTION	FLAGS_LIMIT	FLAGS_TIME_ZONE	FLAGS_SQL_MODE	FLAGS_MAX_SORT_LENGTH	FLAGS_GROUP_CONCAT_MAX_LEN	FLAGS_DIV_PRECISION_INCREMENT	FLAGS_DEFAULT_WEEK_FORMAT	FLAGS_LC_TIME_NAMES
1	teste	select * from t1	3	3	3	0	0	0	0	0				1411247500.713750		232	35	NON TRANSACT	78	1	512	142	1	1	0	0	0	1	1	utf8	utf8	utf8_general_ci	-1	SYSTEM	PIPES_AS_CONCAT,ALLOW_INVALID_DATES	1024	1024	5	0	en_US

QUERY_CACHE_ID

SCHEMA

TABLE_NAME

TABLE_SUFFIX

teste

(here we display partition name like P#p0)

TABLE_SCHEMA

TABLE_NAME

TABLE_HASHED

TABLE_TYPE

QUERIES_IN_CACHE

teste

NON_TRANSACT

[MDEV-4682] QUERY CACHE - add STATISTICS per query and show this informations in qc_info plugin Created: 2013-06-19 Updated: 2015-12-07 Resolved: 2015-09-11
Status:	Closed
Project:	MariaDB Server
Component/s:	Plugins, Query Cache
Fix Version/s:	10.1.8

[MDEV-4682] QUERY CACHE - add STATISTICS per query and show this informations in qc_info plugin Created: 2013-06-19 Updated: 2015-12-07 Resolved: 2015-09-11