Oracle性能诊断艺术-读书笔记

Posted 2020-09-21 ORACLE-fans

20170525
1537
trcsess.awk 工具，使用类似如下：
awk -f trcsess.awk  xxx.trc >  xxx.more


1615
tvdztat -i ....trc -o xxx.html

20170526
1604
select t1.pname,t1.pval1,t1.pval2 from sys.aux_stats$ t1
where t1.sname=‘SYSSTATS_MAIN‘;

select sum(t1.SINGLEBLKRDS) as count,sum(t1.SINGLEBLKRDTIM) time_ms  from v$filestat t1;

create table t as
select rownum as id,
round(dbms_random.normal*1000) as val1,
100+round(ln(rownum/3.25+2 )) as val2,
100+round(ln(rownum/3.25+2 )) as val3,
dbms_random.string(‘p‘,250) as pad
from all_objects
where rownum<=1000
order by dbms_random.value;

update t set val1=null where val1<0;

alter table t add constraints  t_pk primary key(id);

create index t_val1_i on t(val1);

create index t_val2_i on t(val2);

begin
  dbms_stats.gather_table_stats(
 ownname=>user,
 tabname=>‘T‘,
 estimate_percent=>100,
 method_opt =>‘for all columns size skewonly‘,
  cascade=>true);
  end;

select t1.NUM_ROWS,t1.BLOCKS,t1.EMPTY_BLOCKS,t1.AVG_SPACE,t1.CHAIN_CNT,t1.AVG_ROW_LEN
from user_tab_statistics t1
where t1.TABLE_NAME=‘T‘;




  NUM_ROWS     BLOCKS EMPTY_BLOCKS  AVG_SPACE  CHAIN_CNT AVG_ROW_LEN
---------- ---------- ------------ ---------- ---------- -----------
      1000         44            0          0          0         266
      

/*
NUM_ROWS 表中数据的行数
BLOCKS  高水位线以下的数据块个数
EMPTY_BLOCKS 高水位线以上的数据块个数
AVG_SPACE 表中数据块的平均空闲空间（单位：字节）
CHAIN_CNT  涉及行迁移、行链接的总行数
AVG_ROW_LEN 表中平均每个记录的长度（单位：字节）
*/


select t1.column_name name,t1.num_distinct "#dst",t1.low_value,t1.high_value,
t1.density dens,t1.num_nulls "#null",t1.avg_col_len avglen,t1.HISTOGRAM,t1.num_buckets "#bkt"    
from user_tab_col_statistics t1
where t1.table_name=‘T‘;

NAME                                 #dst LOW_VALUE                                                        HIGH_VALUE                                                             DENS      #null     AVGLEN HISTOGRAM             #bkt
------------------------------ ---------- ---------------------------------------------------------------- ---------------------------------------------------------------- ---------- ---------- ---------- --------------- ----------
ID                                   1000 C102                                                             C20B                                                                   .001          0          4 NONE                     1
VAL1                                  457 C105                                                             C22160                                                           .002353264        481          3 HEIGHT BALANCED        254
VAL2                                    6 C20202                                                           C20207                                                                .0005          0          4 FREQUENCY                6
VAL3                                    6 C20202                                                           C20207                                                                .0005          0          4 FREQUENCY                6
PAD                                  1000 203F2C5D523371586E695D456775533C565A522A4F3128234F43502F77353026 7E7E7438735D7A464E77205B7B79454D517E384069784521344735457E2F2120       .001          0        251 HEIGHT BALANCED        254


select utl_raw.cast_to_number(low_value) as low_value,
utl_raw.cast_to_number(high_value) as high_value
from user_tab_col_statistics
where table_name=‘T‘
and column_name=‘VAL1‘;


/*
LOW_VALUE HIGH_VALUE
---------- ----------
         4       3295
*/

begin
  dbms_stats.gather_index_stats(ownname =>user, indname =>‘T_VAL1_I‘,estimate_percent=>100);
  end;  




select t1.INDEX_NAME,t1.blevel,t1.LEAF_BLOCKS,t1.DISTINCT_KEYS,
t1.NUM_ROWS,t1.CLUSTERING_FACTOR,t1.AVG_LEAF_BLOCKS_PER_KEY,t1.AVG_DATA_BLOCKS_PER_KEY
from user_ind_statistics t1
where t1.TABLE_NAME=‘T‘;


/*
INDEX_NAME                         BLEVEL LEAF_BLOCKS DISTINCT_KEYS   NUM_ROWS CLUSTERING_FACTOR AVG_LEAF_BLOCKS_PER_KEY AVG_DATA_BLOCKS_PER_KEY
------------------------------ ---------- ----------- ------------- ---------- ----------------- ----------------------- -----------------------
T_PK                                    1           2          1000       1000               972                       1                       1
T_VAL1_I                                1           2           457        519               508                       1                       1
T_VAL2_I                                1           3             6       1000               174                       1                      29

BLEVEL 访问叶子快而需要读取的分支块的数量，包括根块
LEAF_BLOCKS 索引中的叶子块数量
DISTINCT_KEYS 索引中唯一键值总数
NUM_ROWS 索引中的键值数，对于主键来说 等同于 DISTINCT_KEYS
CLUSTERING_FACTOR 表明有多少临近的索引条目知道不同的数据块。
如果表中数据和索引的排序是相似的，那么 聚簇因子就小。最小值是表中非空数据的数据块总数
如果表中数据和索引的排序迥异，聚簇因子就非常大。最大值是索引中的键值数

*/



1621
create or replace function clustering_factor(
p_owner in varchar2,
p_table_name in varchar2,
p_column_name in varchar2)
return number is
l_cursor sys_refcursor;
l_clustering_factor binary_integer:=0;
l_block_nr binary_integer:=0;
l_previous_block_nr binary_integer:=0;
l_file_nr binary_integer :=0;
l_previous_file_nr binary_integer:=0;
begin
  open l_cursor for
 ‘ select dbms_rowid.rowid_block_number(rowid) block_nr,‘||
  ‘        dbms_rowid.rowid_to_absolute_fno(rowid,‘‘‘||
          p_owner||‘‘‘,‘‘‘||
          p_table_name||‘‘‘) file_nr ‘||
          ‘FROM ‘ ||p_owner||‘.‘||p_table_name||‘ ‘ ||
          ‘where  ‘||p_column_name||‘ is not null ‘||
          ‘ order by  ‘||p_column_name;
          loop
            fetch l_cursor into l_block_nr,l_file_nr;
            exit when l_cursor%notfound;
            if (l_previous_block_nr <> l_block_nr or l_previous_file_nr <>l_file_nr )
              then
                l_clustering_factor:=l_clustering_factor+1;
                end if;
                l_previous_block_nr:=l_block_nr;
                l_previous_file_nr:=l_file_nr;
                end loop;
                close l_cursor;
                return l_clustering_factor;
 end clustering_factor;


1636
select i.index_name,i.clustering_factor,clustering_factor(user,i.table_name,ic.COLUMN_NAME) as my_clstf
from user_indexes i,user_ind_columns ic
where i.table_name=‘T‘ and i.index_name=ic.INDEX_NAME;


INDEX_NAME                     CLUSTERING_FACTOR   MY_CLSTF
------------------------------ ----------------- ----------
T_PK                                         972        972
T_VAL1_I                                     508        508
T_VAL2_I                                     174        174


1732
锁住对象统计信息
dbms_stats.lock_table_stats(ownname=>user,tabname=>‘table_name‘);
dbms_stats.lock_schema_stats(ownname=>user);

解锁对象统计信息
dbms_stats.unlock_table_stats(ownname=>user,tabname=>‘table_name‘)；
dbms_stats.unlock_schema_stats(ownname=>user);