Sql_Trace File Identifier

我們設置了sql_trace為true之后，trace file會dump到udump中，但是該目錄下也許已經有很多trace file了，或者其他session也設置了sql_trace為true，也在產生trace file。如何能迅速找到你的session產生的trace file呢？我們可以通過如下語句設置Sql_Trace File Identifier：

這樣你的session產生的trace file就會以設置的identifier為后綴。

 

然后我們可以看到udump下生成的trace file文件名為：test_ora_4168_test_identifier.trc

Sample Block

抽樣表掃描（sample table scan）只讀取一個表的部分數據。其實我們只選擇表的部分數據的話，可以用rownum來限制也很方便。但是考慮如下情況：
A表和B表join，我只想A表的部分數據去連接B表，此時用sample就方便的多。如果用rownum就需要用一個subquery。

抽樣表掃描有兩種形式，一種是抽樣表中行數的一個百分比，一個是抽樣表中塊數的一個百分比。注意都是百分比。語法如下：

也可以在視圖上使用SAMPLE。

Kimball在他的ETL Toolkit一書中，一直強調：對于有外鍵約束的表，為了提高load的速度，可以先將外鍵約束disable，加載完成后再enable（當然另外一個原因是進入數據倉庫的數據都是規范的，甚至可以考慮不使用外鍵約束，即違反約束的數據在Transformation部分就應該解決掉，當然這是設計問題了）。ps:另外兩個提高load速度的方法分別為使用sql loader和insert、update分離。當時還不是明白這個過程怎么具體實現，今天看《oracle concept》看到下面話終于明白了一些：
Flexibility for Data Loads and Identification of Integrity Violations
You can disable integrity constraints temporarily so that large amounts of data can be loaded without the overhead of constraint checking. When the data load is complete,you can easily enable the integrity constraints, and you can automatically report any new rows that violate integrity constraints to a separate exceptions table.
看來oracle這點上做的比較完善，還可以將違反完整性約束的數據自動記錄到一個exception表中。

今天google分析函數row_number()的時候發現的，覺得很好：

表demo是重復拷貝自dba_objects，有88萬左右，不重復的是27323，沒有索引
方法一：delete from demo a where a.rowid <> (select max(rowid) from demo b where
b.object_id=a.object_id);
耗時：幾個小時以上
方法二： delete from demo where rowid in
(select rid from
(select rowid rid,row_number() over(partition by object_id order by rowid) rn
from demo)
where rn <> 1 );
耗時：30秒
方法三： create table demo2 as
select object_id,owner... from
(select demo.*,row_number() over(partition by object_id order by rowid) rn from demo)
where rn = 1;
truncate table demo; insert into demo select * from demo2; drop table demo2;
共耗時： 10秒，適合大數據量的情況，產生更少回滾量；

學到了分析函數row_number(),對于object_id和rowid也有了一些認識。oracle要學的東西太多了，什么時候是個頭啊。上面的方法不是很難理解，但也還沒有完全理解，有機會實際試試。

今天在論壇看到的方法，先記錄下來：
方法一：
在sequential file stage中有個屬性可以ignore第一行。對于footer，如果footer使用了與正文不同的格式，可以用使用transformer stage和 @INROWNUM stage來將footer去掉。
方法二：
在sequential file的filter option中使用sed -e '$d' -e '1d'來講header和footer去掉。
方法三：
寫個before job subroutine，可以先對這個文件做各種處理，不過我想也是subroutine中調用DSExecute sed -e '$d' -e '1d'。當然Basic中也有專門對sequential file處理的函數。

Orchadmin is a command line utility provided by datastage to research on data sets.
The general callable format is : $orchadmin [options] [descriptor file]

1. Before using orchadmin, you should make sure that either the working directory or the $APT_ORCHHOME/etc contains the file “config.apt” OR

The environment variable $APT_CONFIG_FILE should be defined for your session.
Orchadmin commands

The various commands available with orchadmin are
1. CHECK: $orchadmin check

Validates the configuration file contents like , accesibility of all nodes defined in the configuration file, scratch disk definitions and accesibility of all the nodes etc. Throws an error when config file is not found or not defined properly

2. COPY : $orchadmin copy
Makes a complete copy of the datasets of source with new destination descriptor file name. Please not that

a. You cannot use UNIX cp command as it justs copies the config file to a new name. The data is not copied.

b. The new datasets will be arranged in the form of the config file that is in use but not according to the old confing file that was in use with the source.

3. DELETE : $orchadmin <> [-f -x] descriptorfiles….
The unix rm utility cannot be used to delete the datasets. The orchadmin delete or rm command should be used to delete one or more persistent data sets.
-f options makes a force delete. If some nodes are not accesible then -f forces to delete the dataset partitions from accessible nodes and leave the other partitions in inaccesible nodes as orphans.
-x forces to use the current config file to be used while deleting than the one stored in data set.

4. DESCRIBE: $orchadmin describe [options] descriptorfile.ds
This is the single most important command.
1. Without any option lists the no.of.partitions, no.of.segments, valid segments, and preserve partitioning flag details of the persistent dataset.
-c : Print the configuration file that is written in the dataset if any
-p: Lists down the partition level information.
-f: Lists down the file level information in each partition
-e: List down the segment level information .
-s: List down the meta-data schema of the information.
-v: Lists all segemnts , valid or otherwise
-l : Long listing. Equivalent to -f -p -s -v -e

5. DUMP: $orchadmin dump [options] descriptorfile.ds
The dump command is used to dump(extract) the records from the dataset.
Without any options the dump command lists down all the records starting from first record from first partition till last record in last partition.
-delim ‘’ : Uses the given string as delimtor for fields instead of space.
-field : Lists only the given field instead of all fields.
-name : List all the values preceded by field name and a colon
-n numrecs : List only the given number of records per partition.
-p period(N) : Lists every Nth record from each partition starting from first record.
-skip N: Skip the first N records from each partition.
-x : Use the current system configuration file rather than the one stored in dataset.

6. TRUNCATE: $orchadmin truncate [options] descriptorfile.ds
Without options deletes all the data(ie Segments) from the dataset.
-f: Uses force truncate. Truncate accessible segments and leave the inaccesible ones.
-x: Uses current system config file rather than the default one stored in the dataset.
-n N: Leaves the first N segments in each partition and truncates the remaining.

7. HELP: $orchadmin -help OR $orchadmin -help
Help manual about the usage of orchadmin or orchadmin commands