DBMS_STATS
The DBMS_STATS package was introduced in Oracle 8i and is Oracles preferred method of gathering object statistics. Oracle list a number of benefits to using it including parallel execution, long term storage of statistics and transfer of statistics between servers. Once again, it follows a similar format to the other methods:

EXEC DBMS_STATS.gather_database_stats;
EXEC DBMS_STATS.gather_database_stats(estimate_percent => 15);

EXEC DBMS_STATS.gather_schema_stats('SCOTT');
EXEC DBMS_STATS.gather_schema_stats('SCOTT', estimate_percent => 15);

EXEC DBMS_STATS.gather_table_stats('SCOTT', 'EMPLOYEES');
EXEC DBMS_STATS.gather_table_stats('SCOTT', 'EMPLOYEES', estimate_percent => 15);

EXEC DBMS_STATS.gather_index_stats('SCOTT', 'EMPLOYEES_PK');
EXEC DBMS_STATS.gather_index_stats('SCOTT', 'EMPLOYEES_PK', estimate_percent => 15);
This package also gives you the ability to delete statistics:

EXEC DBMS_STATS.delete_database_stats;
EXEC DBMS_STATS.delete_schema_stats('SCOTT');
EXEC DBMS_STATS.delete_table_stats('SCOTT', 'EMPLOYEES');
EXEC DBMS_STATS.delete_index_stats('SCOTT', 'EMPLOYEES_PK');

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自從Oracle8.1.5引入dbms_stats包，Experts們便推薦使用dbms_stats取代analyze。 理由如下

dbms_stats可以并行分析
dbms_stats有自動(dòng)分析的功能(alter table monitor )
analyze 分析統(tǒng)計(jì)信息的不準(zhǔn)確some times

1,2好理解，且第2點(diǎn)實(shí)際上在VLDB中是最吸引人的；3以前比較模糊，看了metalink236935.1 解釋，analyze在分析Partition表的時(shí)候，有時(shí)候會(huì)計(jì)算出不準(zhǔn)確的Global statistics .

原因是，dbms_stats會(huì)實(shí)在的去分析表全局統(tǒng)計(jì)信息（當(dāng)指定參數(shù)）；而analyze是將表分區(qū)（局部）的statistics 匯總計(jì)算成表全局statistics ,可能導(dǎo)致誤差。

如果想分析整個(gè)用戶或數(shù)據(jù)庫(kù)，還可以采用工具包，可以并行分析
Dbms_utility(8i以前的工具包)
Dbms_stats(8i以后提供的工具包)
如
dbms_stats.gather_schema_stats(User,estimate_percent=>100,cascade=> TRUE);
dbms_stats.gather_table_stats(User,TableName,degree => 4,cascade => true);

這是對(duì)命令與工具包的一些總結(jié)

1、對(duì)于分區(qū)表，建議使用DBMS_STATS，而不是使用Analyze語(yǔ)句。
a) 可以并行進(jìn)行，對(duì)多個(gè)用戶，多個(gè)Table
b) 可以得到整個(gè)分區(qū)表的數(shù)據(jù)和單個(gè)分區(qū)的數(shù)據(jù)。
c) 可以在不同級(jí)別上Compute Statistics：?jiǎn)蝹€(gè)分區(qū)，子分區(qū)，全表，所有分區(qū)
d) 可以倒出統(tǒng)計(jì)信息
e) 可以用戶自動(dòng)收集統(tǒng)計(jì)信息

2、DBMS_STATS的缺點(diǎn)
a) 不能Validate Structure
b) 不能收集CHAINED ROWS, 不能收集CLUSTER TABLE的信息，這兩個(gè)仍舊需要使用Analyze語(yǔ)句。
c) DBMS_STATS 默認(rèn)不對(duì)索引進(jìn)行Analyze，因?yàn)槟J(rèn)Cascade是False，需要手工指定為True

3、對(duì)于oracle 9里面的External Table，Analyze不能使用，只能使用DBMS_STATS來收集信息。

-----------------------------------------------------------------
10G的文檔是這么說的：
Do not use the COMPUTE and ESTIMATE clauses of ANALYZE to collect optimizer statistics. These clauses are supported for backward compatibility. Instead, use the DBMS_STATS package, which lets you collect statistics in parallel, collect global statistics for partitioned objects, and fine tune your statistics collection in other ways. The cost-based optimizer, which depends upon statistics, will eventually use only statistics that have been collected by DBMS_STATS

analyze的功能已經(jīng)明確：
Use the ANALYZE statement (rather than DBMS_STATS) forstatistics collection not related to the cost-based optimizer:

To use the VALIDATE or LIST CHAINED ROWS clauses

To collect information on freelist blocks

在收集與CBO優(yōu)化器不相關(guān)的統(tǒng)計(jì)信息的時(shí)候ANALYZE語(yǔ)句要優(yōu)于DBMS_STATS包

-----------------------------------
EX:
begin
for owner in (select username from dba_users where username not in ('SYS','SYSTEM'))
loop
dbms_output.disable;
dbms_output.enable(1000000);
dbms_output.put_line('Schema: '||owner.username);
select sysdate into start_time from dual;
dbms_output.put_line('Analyze start from : '||start_time);
dbms_stats.gather_schema_stats(ownname => owner.username, estimate_percent => 20, block_sample=> true, cascade=>true);
select sysdate into end_time from dual;
dbms_output.put_line('Analyze complete at : '||end_time);
dbms_output.put_line('---------------------------');
end loop;

dbms_stats.gather_table_stats(ownname =>,
tabname =>,
partname =>,
estimate_percent =>,
block_sample =>,
method_opt =>,
degree =>,parallel degree(并行收集維度)　看CPU個(gè)數(shù)
granularity =>,
cascade =>,true is also gather columns and index’s statistics;
no_invalidate =>);

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當(dāng)索引整個(gè)塊成為空塊的時(shí)候，會(huì)被放置于freelist上，可以被重用。但是重用前結(jié)構(gòu)上還是臨時(shí)放置于B-Tree中。

這時(shí)analyze & dbms_stats在分析時(shí)會(huì)有不同，analyze會(huì)將這些空的block計(jì)算為leaf block，而dbms_stats不將其計(jì)算在內(nèi)。

請(qǐng)看例子

1  create table test
2  as
3  select rownum x
4* from dba_objects
SQL> /

Table created.

SQL> select count(*) from test;

COUNT(*)
———-
6114

1  create index test_idx on test(x)
2* pctfree 95
SQL> /

Index created.

SQL> analyze table test compute statistics;

Table analyzed.

SQL> select index_name,blevel,leaf_blocks,distinct_keys,num_rows,last_analyzed  from dba_indexes where index_name=’TEST_IDX’ and owner=’SYS’;

INDEX_NAME                         BLEVEL LEAF_BLOCKS DISTINCT_KEYS   NUM_ROWS LAST_ANALYZED
—————————— ———- ———– ————- ———- —————–
TEST_IDX                                1         408          6114       6114 20060513 01:00:25

SQL> delete from test where x<3000;

2999 rows deleted.

SQL> commit;

Commit complete.

SQL> analyze index test_idx compute statistics;

Index analyzed.

SQL> select index_name,blevel,leaf_blocks,distinct_keys,num_rows,last_analyzed
2  from dba_indexes where index_name=’TEST_IDX’ and owner=’SYS’;

INDEX_NAME                         BLEVEL LEAF_BLOCKS DISTINCT_KEYS   NUM_ROWS LAST_ANALYZED
—————————— ———- ———– ————- ———- —————–
TEST_IDX                                1         408          3115       3115 20060513 01:03:31

SQL> exec DBMS_STATS.GATHER_INDEX_STATS(’SYS’,'TEST_IDX’);

PL/SQL procedure successfully completed.

SQL>  select index_name,blevel,leaf_blocks,distinct_keys,num_rows,last_analyzed
2   from dba_indexes where index_name=’TEST_IDX’ and owner=’SYS’;

INDEX_NAME                         BLEVEL LEAF_BLOCKS DISTINCT_KEYS   NUM_ROWS LAST_ANALYZED
—————————— ———- ———– ————- ———- —————–
TEST_IDX                                1         209          3115       3115 20060513 01:04:28

FROM:http://www./blog/?p=21

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我們知道從oracle8i開始﹐analyze語(yǔ)句和dbms_stats包都可以收集相關(guān)對(duì)象(Tables﹑Indexes﹑Clusters and Materialized Views)的statistics。那哪些statistics的收集應(yīng)該使用analyze語(yǔ)句﹐哪些statistics的收集應(yīng)該使用dbms_stats包呢﹖

對(duì)于使用哪個(gè)去收集statistics﹐應(yīng)該把一個(gè)原則﹐凡是與cost-based optimizer相關(guān)的statistics﹐都應(yīng)通過dbms_stats包收集。與cost-based optimizer無關(guān)的statistics(如empty blocks﹐average space等)都應(yīng)通過analyze語(yǔ)句去收集。

之所以要用dbms_stats包去替代analyze收集優(yōu)化器statistics﹐是因?yàn)閐bms_stats包能收集并行statistics和分區(qū)對(duì)象的全局statistics。

當(dāng)然analyze語(yǔ)句在其它方面的statistics收集﹐是dbms_stats所無法取代的﹐如﹕

1. 收集在freelist上的blocks信息

2. 檢驗(yàn)存儲(chǔ)格式的合法性

analyze table bk_test_t validate structure cascade online;

3. 識(shí)別表或cluster的行遷移與行鏈接

為了能使用analyze….list chained rows語(yǔ)句識(shí)別行遷移與行鏈接﹐必須先在執(zhí)行analyze語(yǔ)句所在的schema內(nèi)執(zhí)行$ORACLE_HOME/rdbms/admin/utlchain.sql(或utlchn1.sql)腳本建立chained_rows表。在chained_rows建立之后﹐就可以執(zhí)行下面的語(yǔ)句﹕

analyze table bk_test list chained rows into chained_rows;

from:http://space./?uid-33600-action-viewspace-itemid-266418

本文來自CSDN博客，轉(zhuǎn)載請(qǐng)標(biāo)明出處：http://blog.csdn.net/aicon/archive/2010/04/12/5474240.aspx