為什么80%的碼農(nóng)都做不了架構(gòu)師？>>> ??

大家做過統(tǒng)計(jì)的一些存儲(chǔ)過程可能會(huì)知道，我們經(jīng)常有這類表，要先truncate它，執(zhí)行插入，再在執(zhí)行相關(guān)sql，這就會(huì)導(dǎo)致有一個(gè)時(shí)間誤差，如果在truncate和插入的中間進(jìn)行了表的分析，這個(gè)統(tǒng)計(jì)信息是不準(zhǔn)確的，也會(huì)影響執(zhí)行計(jì)劃：

?

[sql] view plain copy print ?

SQL>?select?num_rows,blocks??from?user_tables;???

??

??NUM_ROWS?????BLOCKS??

----------?----------??

?????50315????????103??

??

SQL>?turncate?table?daodao_temp;??

SP2-0734:?unknown?command?beginning?"turncate?t..."?-?rest?of?line?ignored.??

SQL>?truncate?table?daodao_temp;??

??

Table?truncated.??

??

SQL>?select?num_rows,blocks??from?user_tables;???

??

??NUM_ROWS?????BLOCKS??

----------?----------??

?????50315????????103??

??

SQL>?execute?dbms_stats.gather_table_stats(user,'DAODAO_TEMP');??

??

PL/SQL?procedure?successfully?completed.??

??

SQL>?select?num_rows,blocks??from?user_tables;???

??

??NUM_ROWS?????BLOCKS??

----------?----------??

?????????0??????????0??

SQL> select num_rows,blocks from user_tables; NUM_ROWS BLOCKS ---------- ----------50315 103SQL> turncate table daodao_temp; SP2-0734: unknown command beginning "turncate t..." - rest of line ignored. SQL> truncate table daodao_temp;Table truncated.SQL> select num_rows,blocks from user_tables; NUM_ROWS BLOCKS ---------- ----------50315 103SQL> execute dbms_stats.gather_table_stats(user,'DAODAO_TEMP');PL/SQL procedure successfully completed.SQL> select num_rows,blocks from user_tables; NUM_ROWS BLOCKS ---------- ----------0 0

?

?--這里是關(guān)鍵點(diǎn)，我們有個(gè)按天分析的job，如果這個(gè)時(shí)候分析了這個(gè)數(shù)據(jù)，會(huì)認(rèn)為數(shù)據(jù)為0，但是之后就是錄入數(shù)據(jù)到臨時(shí)表

?

SQL> select num_rows,blocks? from user_tables;

? NUM_ROWS???? BLOCKS
---------- ----------
???????? 0????????? 0

SQL> insert into daodao_temp select object_id,object_id from dba_objects;

50315 rows created.

SQL> commit;

Commit complete.

有數(shù)據(jù)進(jìn)行入庫(kù)：

好了，這個(gè)時(shí)候已經(jīng)不會(huì)再執(zhí)行統(tǒng)計(jì)信息的存儲(chǔ)過程了（除非第二天的時(shí)候），這個(gè)時(shí)候如果有一個(gè)sql執(zhí)行，就會(huì)導(dǎo)致執(zhí)行計(jì)劃可能錯(cuò)誤了。

這種現(xiàn)象在月初尤其明顯，道理類似的。

我們可以對(duì)這類臨時(shí)表進(jìn)行錄入數(shù)據(jù)的鎖定統(tǒng)計(jì)信息：

SQL> execute dbms_stats.gather_table_stats(user,'DAODAO_TEMP');

SQL> select num_rows,blocks? from user_tables;

? NUM_ROWS???? BLOCKS
---------- ----------
???? 50315??????? 103

SQL> execute DBMS_STATS.LOCK_TABLE_STATS(user,'DAODAO_TEMP');

PL/SQL procedure successfully completed.

SQL> TRUNCATE TABLE DAODAO_TEMP;

Table truncated.

SQL> execute dbms_stats.gather_table_stats(user,'DAODAO_TEMP');
BEGIN dbms_stats.gather_table_stats(user,'DAODAO_TEMP'); END;

*
ERROR at line 1:
ORA-20005: object statistics are locked (stattype = ALL)
ORA-06512: at "SYS.DBMS_STATS", line 13056
ORA-06512: at "SYS.DBMS_STATS", line 13076
ORA-06512: at line 1

這樣搜集統(tǒng)計(jì)信息的時(shí)候就不會(huì)搜集了，相關(guān)數(shù)據(jù)字典可以查詢這個(gè):

SQL> select stattype_locked from user_tab_statistics where table_name ='DAODAO_TEMP';

STATT
-----
ALL

all表示鎖定了 ，空表示沒有鎖定：

如果需要解鎖，可以執(zhí)行如下:

SQL> execute dbms_stats.unlock_table_stats(user,'DAODAO_TEMP');

PL/SQL procedure successfully completed.

轉(zhuǎn)載于:https://my.oschina.net/farces/blog/664334

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