就执行一条SQL：
DELETE FROM TEMPCACHE WHERE TIMESTAMPDIFF(MINUTE,CRDATETIME,NOW())>=10
总共有3W条数据，删除的时候磁盘IO读写加起来飙到50M，执行要花将近1分钟，就删除大约1.7W条数据。
删完以后还会持续插入，10分钟后又有3W条数据然后继续执行删除，反复这个过程。
这个表其中有个字段是 MEDIUMBLOB 类型，存储的数据大了一点一般是10K-200K的样子。
CRDATETIME字段加了索引，为何这么慢？这因为索引碎片还是什么？怎么优化？
DELETE FROM TEMPCACHE WHERE TIMESTAMPDIFF(MINUTE,CRDATETIME,NOW())>=10
总共有3W条数据，删除的时候磁盘IO读写加起来飙到50M，执行要花将近1分钟，就删除大约1.7W条数据。
删完以后还会持续插入，10分钟后又有3W条数据然后继续执行删除，反复这个过程。
这个表其中有个字段是 MEDIUMBLOB 类型，存储的数据大了一点一般是10K-200K的样子。
CRDATETIME字段加了索引，为何这么慢？这因为索引碎片还是什么？怎么优化？
另外我发现即使条件不符合导致真正被删除的数据只有0条的时候，整个DELETE执行也要耗时几十秒，说明不是删除操作耗时，而是查找符合删除条件的行比较耗时，是索引没生效还是怎样？
select count(0) from TEMPCACHE WHERE CRDATETIME >= (NOW() - INTERVAL 10 minute);
select count(0) from tempcache WHERE TIMESTAMPDIFF(MINUTE,CRDATETIME,NOW())>=10;
这两行SQL，发现结果不一致
这是我的表结构：CREATE TABLE `tempcache` (
`ID` char(36) NOT NULL,
`Content` mediumblob,
`CRDateTime` datetime NOT NULL,
`Status` int(11) NOT NULL,
PRIMARY KEY (`ID`),
UNIQUE KEY `ID_UNIQUE` (`ID`),
KEY `TIME_INDEX` (`CRDateTime`,`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;其中Content字段比较大，平均每条记录存储了30KB的数据。这是我的my.ini配置：[client]
no-beep# pipe
# socket=mysql[mysql]default-character-set=utf8
# SERVER SECTION
# ----------------------------------------------------------------------
#
# The following options will be read by the MySQL Server. Make sure that
# you have installed the server correctly (see above) so it reads this
# file.
#
# server_type=3
[mysqld]
# The TCP/IP Port the MySQL Server will listen on
port=3306# Path to installation directory. All paths are usually resolved relative to this.
# basedir="C:/Program Files/MySQL/MySQL Server 5.6/"# The default character set that will be used when a new schema or table is
# created and no character set is defined
character-set-server=utf8# The default storage engine that will be used when create new tables when
default-storage-engine=INNODB# Set the SQL mode to strict
sql-mode="STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"# Enable Windows Authentication
# plugin-load=authentication_windows.dll# General and Slow logging.
log-output=FILE
general-log=1slow-query-log=1
slow_query_log_file="WIN-3JPGOV43BRO-slow.log"
long_query_time=10# Binary Logging.
# log-bin# Error Logging.
log-error="WIN-3JPGOV43BRO.err"max_connections = 500
max_user_connections = 500query_cache_size=1M# The number of open tables for all threads. Increasing this value
# increases the number of file descriptors that mysqld requires.
# Therefore you have to make sure to set the amount of open files
# allowed to at least 4096 in the variable "open-files-limit" in
# section [mysqld_safe]
table_open_cache=256# Maximum size for internal (in-memory) temporary tables. If a table
# grows larger than this value, it is automatically converted to disk
# based table This limitation is for a single table. There can be many
# of them.
tmp_table_size=3Mthread_cache_size=10myisam_max_sort_file_size=100Gmyisam_sort_buffer_size=6Mkey_buffer_size=8M# Size of the buffer used for doing full table scans of MyISAM tables.
# Allocated per thread, if a full scan is needed.
read_buffer_size=0
read_rnd_buffer_size=0# This buffer is allocated when MySQL needs to rebuild the index in
# REPAIR, OPTIMZE, ALTER table statements as well as in LOAD DATA INFILE
# into an empty table. It is allocated per thread so be careful with
# large settings.
sort_buffer_size=0#*** INNODB Specific options ***
# innodb_data_home_dir=0.0# Use this option if you have a MySQL server with InnoDB support enabled
# but you do not plan to use it. This will save memory and disk space
# and speed up some things.
# skip-innodbinnodb_additional_mem_pool_size=2Minnodb_flush_log_at_trx_commit=1# The size of the buffer InnoDB uses for buffering log data. As soon as
# it is full, InnoDB will have to flush it to disk. As it is flushed
# once per second anyway, it does not make sense to have it very large
# (even with long transactions).
innodb_log_buffer_size=1M# InnoDB, unlike MyISAM, uses a buffer pool to cache both indexes and
# row data. The bigger you set this the less disk I/O is needed to
# access data in tables. On a dedicated database server you may set this
# parameter up to 80% of the machine physical memory size. Do not set it
# too large, though, because competition of the physical memory may
# cause paging in the operating system. Note that on 32bit systems you
# might be limited to 2-3.5G of user level memory per process, so do not
# set it too high.
innodb_buffer_pool_size=8M# Size of each log file in a log group. You should set the combined size
# of log files to about 25%-100% of your buffer pool size to avoid
# unneeded buffer pool flush activity on log file overwrite. However,
# note that a larger logfile size will increase the time needed for the
# recovery process.
innodb_log_file_size=48M# Number of threads allowed inside the InnoDB kernel. The optimal value
# depends highly on the application, hardware as well as the OS
# scheduler properties. A too high value may lead to thread thrashing.
innodb_thread_concurrency=2# The increment size (in MB) for extending the size of an auto-extend InnoDB system tablespace file when it becomes full.
innodb_autoextend_increment=64# The number of regions that the InnoDB buffer pool is divided into.
# For systems with buffer pools in the multi-gigabyte range, dividing the buffer pool into separate instances can improve concurrency,
# by reducing contention as different threads read and write to cached pages.
innodb_buffer_pool_instances=8# Determines the number of threads that can enter InnoDB concurrently.
innodb_concurrency_tickets=5000# Specifies how long in milliseconds (ms) a block inserted into the old sublist must stay there after its first access before
# it can be moved to the new sublist.
innodb_old_blocks_time=1000# It specifies the maximum number of .ibd files that MySQL can keep open at one time. The minimum value is 10.
innodb_open_files=300# When this variable is enabled, InnoDB updates statistics during metadata statements.
innodb_stats_on_metadata=0# When innodb_file_per_table is enabled (the default in 5.6.6 and higher), InnoDB stores the data and indexes for each newly created table
# in a separate .ibd file, rather than in the system tablespace.
innodb_file_per_table=1# Use the following list of values: 0 for crc32, 1 for strict_crc32, 2 for innodb, 3 for strict_innodb, 4 for none, 5 for strict_none.
innodb_checksum_algorithm=0# The number of outstanding connection requests MySQL can have.
# This option is useful when the main MySQL thread gets many connection requests in a very short time.
# It then takes some time (although very little) for the main thread to check the connection and start a new thread.
# The back_log value indicates how many requests can be stacked during this short time before MySQL momentarily
# stops answering new requests.
# You need to increase this only if you expect a large number of connections in a short period of time.
back_log=80# If this is set to a nonzero value, all tables are closed every flush_time seconds to free up resources and
# synchronize unflushed data to disk.
# This option is best used only on systems with minimal resources.
flush_time=0# The minimum size of the buffer that is used for plain index scans, range index scans, and joins that do not use
# indexes and thus perform full table scans.
join_buffer_size=256K# The maximum size of one packet or any generated or intermediate string, or any parameter sent by the
# mysql_stmt_send_long_data() C API function.
max_allowed_packet=4M# If more than this many successive connection requests from a host are interrupted without a successful connection,
# the server blocks that host from performing further connections.
max_connect_errors = 250# Changes the number of file descriptors available to mysqld.
# You should try increasing the value of this option if mysqld gives you the error "Too many open files".
open_files_limit=4161# Set the query cache type. 0 for OFF, 1 for ON and 2 for DEMAND.
query_cache_type=1# If you see many sort_merge_passes per second in SHOW GLOBAL STATUS output, you can consider increasing the
# sort_buffer_size value to speed up ORDER BY or GROUP BY operations that cannot be improved with query optimization
# or improved indexing.
sort_buffer_size=256K# The number of table definitions (from .frm files) that can be stored in the definition cache.
# If you use a large number of tables, you can create a large table definition cache to speed up opening of tables.
# The table definition cache takes less space and does not use file descriptors, unlike the normal table cache.
# The minimum and default values are both 400.
table_definition_cache=400# Specify the maximum size of a row-based binary log event, in bytes.
# Rows are grouped into events smaller than this size if possible. The value should be a multiple of 256.
binlog_row_event_max_size=8K# If the value of this variable is greater than 0, a replication slave synchronizes its master.info file to disk.
# (using fdatasync()) after every sync_master_info events.
sync_master_info=10000# If the value of this variable is greater than 0, the MySQL server synchronizes its relay log to disk.
# (using fdatasync()) after every sync_relay_log writes to the relay log.
sync_relay_log=10000# If the value of this variable is greater than 0, a replication slave synchronizes its relay-log.info file to disk.
# (using fdatasync()) after every sync_relay_log_info transactions.
sync_relay_log_info=10000
performance_schema_max_table_instances = 200总的来说就是执行DELETE FROM TEMPCACHE WHERE TIMESTAMPDIFF(MINUTE,CRDATETIME,NOW())>=10 删除2W条数据，大概花了1.5分钟，是哪里没优化好吗？
Query OK, 0 rows affected (0.00 sec)mysql> delete frm try where ID>0;
ERROR 1064 (42000): You have an error in your SQL
corresponds to your MySQL server version for the r
here ID>0' at line 1
mysql> delete from try where ID>0;
ERROR 1146 (42S02): Table 'try.try' doesn't exist
mysql> delete from tempcache where ID>0;
Query OK, 1328 rows affected (0.01 sec)