Re: How does "describe" work (difficult)

In article <a069nn$2ni5_at_imsp212.netvigator.com>, "Kai says...
>
>Is there any way to force clear the cache?

alter system flush shared_pool;

>
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>Kai Yuen Kiang
>
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>> In article <87vgezw1zd.fsf_at_altavista.net>, Martin says...
>> >
>> >I know how one could write a "describe" command by querying the data
>> >dictionary, but recently I made a strange observation:
>> >
>> >I turned on sqltrace, ran a "describe" command and turned sqltrace
>> >back off. The trace file showed the "trace on" and "trace off"
>> >commands but the "describe" command itself literally left no trace at
>> >all.
>> >
>> >How could sqlplus possibly implement a describe command without causing
>> >an sqltrace ? Also it is amazingly fast, even when you describe a
>> >table at the other end of a database link which is aliased by a
>> >synonym.
>> >
>>
>> it gets it from the dictionary cache. If you fire up an instance or
>describe
>> something that hasn't been described, you'll see the recursive SQL used to
>get
>> the info into the dictionary cache.
>>
>> When you DON'T see the SQL being executed -- that just means the info was
>in the
>> dictionary cache.
>>
>> >I also ran "strace sqlplus". This showed a socked write and a socked
>> >read. This is no surprise, all commands basically look like like this
>> >(not just describe). I believe this is just classic SQL*Net
>> >communication. I don't know WHAT it writes though.
>>
>> --
>> Thomas Kyte (tkyte@us.oracle.com) http://asktom.oracle.com/
>> Expert one on one Oracle, programming techniques and solutions for Oracle.
>> http://www.amazon.com/exec/obidos/ASIN/1861004826/
>> Opinions are mine and do not necessarily reflect those of Oracle Corp
>>
>
>

--
Thomas Kyte (tkyte@us.oracle.com)             http://asktom.oracle.com/ 
Expert one on one Oracle, programming techniques and solutions for Oracle.
http://www.amazon.com/exec/obidos/ASIN/1861004826/  
Opinions are mine and do not necessarily reflect those of Oracle Corp