教你轻松掌握Informix数据库的日常维护

检查各个dbspaces的空间使用状况：

select name dbspace,sum(chksize) allocated,sum(nfree) free,

round(((sum(chksize)-sum(nfree))/sum(chksize))*100)||"%" pcused

form sysdbspaces d,syschunks c

where d.dbsnum=c.dbsnum group by name order by 4 desc

剩余空间肯定是越大越好了

显示各个dbspaces的I/O状况：

select d.name,fname path_name,sum(pagesread) diskreads,sum(pageswritten) diskwrites

from syschkio c,syschunks k,sysdbspaces d

where d.dbsnum=k.dbsnum and k.chknum=c.chunknum

group by 1,2 order by 3 desc

根据各个dbspaces的I/O来调整表的布局，使整个系统I/O均衡

检查哪个表具有最多的磁盘I/0：

select dbsname, tabname, (isreads + pagreads) diskreads, (iswrites + pagwrites) diskwrites

from sysptPRof

order by 3 desc,4 desc

同上。

检查表的extent的分布状况：

select t.tabname, count(*) num_ext

from sysextents e, npmdb:systables t

where e.tabname=t.tabname

and dbsname = "npmdb"

and t.tabname not like "sys%"

group by 1

having count(*) > 1

order by 2 desc

表的extent建议最大不超过30个，如果太大，就需要重建表修改extent size的大小从而修改extent的数量

检查表中索引的层数（越少越好）：

select idxname, levels from sysindexes order by 2 desc

检查命中率不高的索引(nrows和unique越接近越好）：

select tabname, idxname, nrows, nunique

from systables t, sysindexes I

where t.tabid =i.tabid and t.tabid > 99

and nrows > 0 and nunique > 0

当索引的效率不高的时候，需要根据实际情况修改

看数据库里面那些表的碎片比较多（碎片小比较好）

select dbsname , tabname ,count(*), sum(size)

from sysextents

group by 1,2

order by 3 desc;

表和索引的读写情况，(考查那个数据库实体读写比较多)

select dbsname, tabname, (isreads + pagreads) diskreads, (iswrites + pagwrites)

diskwrites

from sysptprof

order by 3 desc, 4 desc

那些表的锁竞争比较厉害(越小越好)

select a.tabname,nrows,lockwts,deadlks

from sysmaster:sysptprof a,systables b

where a.tabname=b.tabname and lockwts>0

and a.dbsname = 库名

and b.tabid >= 100

order by tabname;

表的顺序扫描数（OLTP系统的话，大表的顺序扫描数越小越好）

select a.tabname,nrows,seqscans

from sysmaster:sysptprof a,systables b

where a.tabname=b.tabname and seqscans>0

and a.dbsname = '库名'

and b.tabid>=100

order by tabname;