MySQL压力测试SHOW VARIABLES过多

  系统做压力测试，数据库产生了性能瓶颈，MySQL压力测试SHOW VARIABLES过多。

# Rank Query ID           Response time    Calls R/Call V/M   Item

# ==== ================== ================ ===== ====== ===== ============
#    1 0xC69B6ED2C47380A4 53851.5307 98.8% 71899 0.7490  0.04 SHOW VARIABLES

# MISC 0xMISC               637.4117  1.2%   888 0.7178   0.0 <2 ITEMS>

# Query 1: 239.66 QPS, 179.51x concurrency, ID 0xC69B6ED2C47380A4 at byte 2506206
# This item is included in the report because it matches --limit.
# Scores: V/M = 0.04
# Time range: 2018-05-03 20:00:46 to 20:05:46
# Attribute    pct   total     min     max     avg     95%  stddev  median
# ============ === ======= ======= ======= ======= ======= ======= =======
# Count         98   71899
# Exec time     98  53852s   500ms      2s   749ms   992ms   183ms   705ms
# Lock time    100      9s    50us     4ms   127us   260us   104us    98us
# Rows sent     99   1.17M      17      17      17      17       0      17
# Rows examine 100   1.17M      17      17      17      17       0      17
# Query size    99  62.81M     916     916     916     916       0     916
# String:
# Hosts        XX.XX.XX.XX (7249/10%)... 13 more
# Users        XXXXXX
# Query_time distribution
#   1us
#  10us
# 100us
#   1ms
#  10ms
# 100ms  ################################################################
#    1s  ######
#  10s+
/* mysql-connector-java-5.1.29 ( Revision: [email protected] ) */SHOW VARIABLES WHERE Variable_name ='language' OR Variable_name = 'net_write_timeout' OR Variable_name = 'interactive_timeout' OR Variable_name = 'wait_timeout' OR Variable_name = 'character_set_client' OR Variable_name = 'character_set_connection' OR Variable_name = 'character_set' OR Variable_name = 'character_set_server' OR Variable_name = 'tx_isolation' OR Variable_name = 'transaction_isolation' OR Variable_name = 'character_set_results' OR Variable_name = 'timezone' OR Variable_name = 'time_zone' OR Variable_name = 'system_time_zone' OR Variable_name = 'lower_case_table_names' OR Variable_name = 'max_allowed_packet' OR Variable_name = 'net_buffer_length' OR Variable_name = 'sql_mode' OR Variable_name = 'query_cache_type' OR Variable_name = 'query_cache_size' OR Variable_name = 'init_connect'\G
 SHOW VARIABLES的是由于mysql-connector-java-5.1.29产生的，当新产生一个连接的时候就会生成一条这样的语句。我想本质上让JDBC少创建连接，要连接池的连接最好是始终保持。

原始：
maxActive="300" maxIdle="30" maxWait="10000" initialSize="30" removeAbandoned="true" logAbandoned="true" name="DataSource"
password="xx#88" type="javax.sql.DataSource" testWhileIdle="true"
timeBetweenEvictionRunsMillis="10000" minEvictableIdleTimeMillis="10000"
testOnBorrow="true" testOnReturn="false" 
validationQuery="select 1"
url="jdbc:mysql://xx.xx.xx.xx:3306/xx?autoReconnect=true&autoReconnectForPools=true" username="xx" />
改进之后：
一般maxIdle与maxAcitve的值应尽量接近，可以取maxIdle=maxActive。这样可以避免高负荷系统频繁创建与销毁连接。
testOnBorrow指定连接被调用时是否经过校验，如果校验未通过，则该连接被连接池断掉，并由连接池尝试调用另一个连接 值为true
testOnReturn指定连接返回到池中是时是否经过校验值为true
maxWait连接池中连接用完时，新的请求的等待时间（即等待别的连接空闲），超时返回异常，毫秒
timeBetweenEvictionRunsMillis = "30000"  每30秒运行一次空闲连接回收器  
minEvictableIdleTimeMillis = "1800000"  池中的连接空闲默认为半小时后被回收  
maxActive="300" maxIdle="300" maxWait="10000" initialSize="100" removeAbandoned="true" logAbandoned="true" name="DataSource"
password="xx#88" type="javax.sql.DataSource" testWhileIdle="true"
timeBetweenEvictionRunsMillis="3600000" minEvictableIdleTimeMillis="3600000"
testOnBorrow="false" testOnReturn="false" 
validationQuery="select 1"
url="jdbc:mysql://xx.xx.xx.xx:3306/xx?autoReconnect=true&autoReconnectForPools=true" username="xx" />

调整之后，就没有产生SHOW VARIABLES的语句。