MySQL的conv函数
继续学习MySQL，这篇记录下conv函数。conv函数用于数字的进制转换，共有三个参数：
N是要转换的数据，from_base是原进制，to_base是目标进制。
+----------------+
| conv(16,10,16) |
+----------------+
| 10 |
+----------------+
1 row in set (0.04 sec)
如果N是有符号数字，则to_base要以负数的形式提供，否则会将N当作无符号数
+------------------+
| conv(-16,10,16) |
+------------------+
| FFFFFFFFFFFFFFF0 |
+------------------+
1 row in set (0.00 sec)
mysql> select conv(-16,10,-16);
+------------------+
| conv(-16,10,-16) |
+------------------+
| -10 |
+------------------+
1 row in set (0.00 sec)
除了conv，还有几个特定进制转换的函数，如：
- hex(N)相当于conv(N,10,16)
- oct(N)相当于conv(N,10,8)
- bin(N)相当于conv(N,10,2)
另外还有一个convert函数用于转换不同的数据类型的，不要和conv搞混淆了。
MySQL的benchmark函数
MySQL实现了很多独特的函数，有时候使用起来是非常的方便，或许这就是开源的好处吧。这里记录一下benchmark函数，一个用于测试MySQL函数性能的函数。benchmark函数只有两个参数，第一个是执行次数，第二个是要测试的函数或者表达式。返回的结果始终是0，执行时间才是我们需要的结果：
+-------------------------------+
| benchmark(1e8,current_date()) |
+-------------------------------+
| 0 |
+-------------------------------+
1 row in set (31.08 sec)
mysql> select benchmark(1e8,abs(1));
+-----------------------+
| benchmark(1e8,abs(1)) |
+-----------------------+
| 0 |
+-----------------------+
1 row in set (1.31 sec)
除法的效率明显不如乘法：
+--------------------+
| benchmark(1e8,1*1) |
+--------------------+
| 0 |
+--------------------+
1 row in set (1.45 sec)
mysql> select benchmark(1e8,1/1);
+--------------------+
| benchmark(1e8,1/1) |
+--------------------+
| 0 |
+--------------------+
1 row in set (19.47 sec)
Oracle11g部分新特性移植到9i和10g
Oracle10.2.0.4出来的时候包含了属于Oracle11g的新特性Real Application Testing，现在，通过patch，可以在9i～10g各版本中获得包括SQL Performance Analyzer和Database Replay在内的Oracle11g新特性。
SQL Performance Analyzer可用于诊断由于系统改变等引起的SQL性能问题，通过在做出改变前后收集一个性能统计报告，然后比较得到性能改变的主要原因。
Database Replay则可以捕获产品数据库的压力等，在测试数据库中进行重演，可以更加准确的模拟产品库的压力对应用进行测试，这也是Oracle11g主推的Real Application Testing的主要功能。
要获得这两个新特性，需要安装Patch，对应的Patch请参考：Metalink Note:560977.1
MySQL压力测试工具mysqlslap
MySQL从5.1.4版开始带有一个压力测试工具mysqlslap，通过模拟多个并发客户端访问mysql来执行测试，使用起来非常的简单。通过mysqlslap –help可以获得可用的选项，这里列一些主要的参数，更详细的说明参考官方手册。
–auto-generate-sql, -a
自动生成测试表和数据–auto-generate-sql-load-type=type
测试语句的类型。取值包括：read，key，write，update和mixed(默认)。–number-char-cols=N, -x N
自动生成的测试表中包含多少个字符类型的列，默认1–number-int-cols=N, -y N
自动生成的测试表中包含多少个数字类型的列，默认1–number-of-queries=N
总的测试查询次数–query=name,-q
使用自定义脚本执行测试，例如可以调用自定义的一个存储过程或者sql语句来执行测试。–create-schema
测试的schema，MySQL中schema也就是database–commint=N
多少条DML后提交一次–compress, -C
如果服务器和客户端支持都压缩，则压缩信息传递–concurrency=N, -c N
并发量，也就是模拟多少个客户端同时执行select。可指定多个值，以逗号或者–delimiter参数指定的值做为分隔符–engine=engine_name, -e engine_name
创建测试表所使用的存储引擎，可指定多个–iterations=N, -i N
测试执行的迭代次数–detach=N
执行N条语句后断开重连–debug-info, -T
打印内存和CPU的信息–only-print
只打印测试语句而不实际执行
测试的过程需要生成测试表，插入测试数据，这个mysqlslap可以自动生成，默认生成一个mysqlslap的schema，如果已经存在则先删除，这里要注意了，不要用–create-schema指定已经存在的库，否则后果可能很严重。可以用–only-print来打印实际的测试过程：
DROP SCHEMA IF EXISTS `mysqlslap`;
CREATE SCHEMA `mysqlslap`;
use mysqlslap;
CREATE TABLE `t1` (intcol1 INT(32) ,charcol1 VARCHAR(128));
INSERT INTO t1 VALUES (1804289383,'mxvtvmC9127qJNm06sGB8R92q2j7vTiiITRDGXM9ZLzkdekbWtmXKwZ2qG1llkRw5m9DHOFilEREk3q7oce8O3BEJC0woJsm6uzFAEynLH2xCsw1KQ1lT4zg9rdxBL');
...
SELECT intcol1,charcol1 FROM t1;
INSERT INTO t1 VALUES (364531492,'qMa5SuKo4M5OM7ldvisSc6WK9rsG9E8sSixocHdgfa5uiiNTGFxkDJ4EAwWC2e4NL1BpAgWiFRcp1zIH6F1BayPdmwphatwnmzdwgzWnQ6SRxmcvtd6JRYwEKdvuWr');
DROP SCHEMA IF EXISTS `mysqlslap`;
可以看到最后由删除一开始创建的schema的动作，整个测试完成后不会在数据库中留下痕迹。假如我们执行一次测试，分别50和100个并发，执行1000次总查询，那么：
Benchmark
Average number of seconds to run all queries: 0.375 seconds
Minimum number of seconds to run all queries: 0.375 seconds
Maximum number of seconds to run all queries: 0.375 seconds
Number of clients running queries: 50
Average number of queries per client: 20
Benchmark
Average number of seconds to run all queries: 0.453 seconds
Minimum number of seconds to run all queries: 0.453 seconds
Maximum number of seconds to run all queries: 0.453 seconds
Number of clients running queries: 100
Average number of queries per client: 10
User time 0.29, System time 0.11
Maximum resident set size 0, Integral resident set size 0
Non-physical pagefaults 4032, Physical pagefaults 0, Swaps 0
Blocks in 0 out 0, Messages in 0 out 0, Signals 0
Voluntary context switches 7319, Involuntary context switches 681
上结果可以看出，50和100个并发分别得到一次测试结果(Benchmark)，并发数越多，执行完所有查询的时间越长。为了准确起见，可以多迭代测试几次:
Benchmark
Average number of seconds to run all queries: 0.380 seconds
Minimum number of seconds to run all queries: 0.377 seconds
Maximum number of seconds to run all queries: 0.385 seconds
Number of clients running queries: 50
Average number of queries per client: 20
Benchmark
Average number of seconds to run all queries: 0.447 seconds
Minimum number of seconds to run all queries: 0.444 seconds
Maximum number of seconds to run all queries: 0.451 seconds
Number of clients running queries: 100
Average number of queries per client: 10
User time 1.44, System time 0.67
Maximum resident set size 0, Integral resident set size 0
Non-physical pagefaults 17922, Physical pagefaults 0, Swaps 0
Blocks in 0 out 0, Messages in 0 out 0, Signals 0
Voluntary context switches 36796, Involuntary context switches 4093
测试同时不同的存储引擎的性能进行对比：
Benchmark
Running for engine myisam
Average number of seconds to run all queries: 0.200 seconds
Minimum number of seconds to run all queries: 0.188 seconds
Maximum number of seconds to run all queries: 0.210 seconds
Number of clients running queries: 50
Average number of queries per client: 20
Benchmark
Running for engine myisam
Average number of seconds to run all queries: 0.238 seconds
Minimum number of seconds to run all queries: 0.228 seconds
Maximum number of seconds to run all queries: 0.251 seconds
Number of clients running queries: 100
Average number of queries per client: 10
Benchmark
Running for engine innodb
Average number of seconds to run all queries: 0.375 seconds
Minimum number of seconds to run all queries: 0.370 seconds
Maximum number of seconds to run all queries: 0.379 seconds
Number of clients running queries: 50
Average number of queries per client: 20
Benchmark
Running for engine innodb
Average number of seconds to run all queries: 0.443 seconds
Minimum number of seconds to run all queries: 0.440 seconds
Maximum number of seconds to run all queries: 0.447 seconds
Number of clients running queries: 100
Average number of queries per client: 10
User time 2.83, System time 1.66
Maximum resident set size 0, Integral resident set size 0
Non-physical pagefaults 34692, Physical pagefaults 0, Swaps 0
Blocks in 0 out 0, Messages in 0 out 0, Signals 0
Voluntary context switches 87306, Involuntary context switches 10326
