nformix调优之执行计划取得

首先编辑q.sql如下

set explain on;

set explain off;

set explain on avoid_execute;

set explain file  to "/tmp/temp.out";

select count(*)  from systables;

select first 1 date(current) from systables #此处换成任意需要调整的sql

登陆informix服务器,执行dbaccess dbname a.sql结果如下

Database selected.

Explain set.

Explain set.

Explain set.

Explain set.

      (count(*)) 

            1142

1 row(s) retrieved.

(expression) 

11/20/2012

1 row(s) retrieved.

Database closed.

查看详细任务计划 more /tmp/temp.out如下

UERY: (OPTIMIZATION TIMESTAMP: 11-20-2012 15:04:13)

------

select count(*)  from tfa_alarm_relation

Estimated Cost: 1

Estimated # of Rows Returned: 1

  1) informix.tfa_alarm_relation: INDEX PATH

    (1) Index Name: (count)

        Index Keys: (count)

Query statistics:

-----------------

  Table map :

  ----------------------------

  Internal name     Table name

  ----------------------------

  type     rows_prod  est_rows  rows_cons  time

  -------------------------------------------------

  group    1          1         0          00:00.00

QUERY: (OPTIMIZATION TIMESTAMP: 11-20-2012 15:04:13)

------

select first 1 date(current) from systables

Estimated Cost: 78

Estimated # of Rows Returned: 1142

  1) informix.systables: SEQUENTIAL SCAN

Query statistics:

-----------------

  Table map :

  ----------------------------

  Internal name     Table name

  ----------------------------

  t1                systables

  type     table  rows_prod  est_rows  rows_scan  time       est_cost

  -------------------------------------------------------------------

  scan     t1     1          1142      3          00:00.00   78      

QUERY: (OPTIMIZATION TIMESTAMP: 11-20-2012 15:06:55)

------

select count(*)  from systables

Estimated Cost: 1

Estimated # of Rows Returned: 1

  1) informix.systables: INDEX PATH

根据任务计划可以看出sql在哪一个环境耗时过长，进而对其进行优化。 

下一节找一个这样的sql进行针对性练习