Re: Does oracle db serialize concurrent read-only SELECT ?

Oracle does not do anything to serialized read-only queries - however you could get this type of behaviour if you query were CPU bound or I/O bound in the first place.

Are you running a small volume query
to do the test, or are you (for example) running a tablescan across a 256MB
table as the base query ?

--
Jonathan Lewis
Yet another Oracle-related web site:  http://www.jlcomp.demon.co.uk

Practical Oracle 8i:  Building Efficient Databases
Publishers:  Addison-Wesley

Reviews at: http://www.jlcomp.demon.co.uk/book_rev.html



Jung Tjong wrote in message <3ADC8EDF.28D814E2_at_cisco.com>...


>I'm new to Oracle, and while testing multiple

>concurrent select request I found that

>the server seems to serialize cursor SELECT done from multiple

>threads or processes, Java (jdbc) or C++ (oci).

>

>There is no write operations on the table,

>so there should not be any lock on it.

>I'm doing a simple SELECT from 1 table and

>measure the time it takes to execute the select and fetch

>all the rows. The result of N concurrent SELECT are

>approximately N times a single SELECT.

>

>I'm using ORACLE 8i - (No parallel server)

>I tried changing server parameters that may relate to this:

>   max_cursor

>   processes

>   open_links

>   mts_servers

>   parallel_max_servers

>   parallel_threads_percpu

>I tried changing connection network parameters in the listener.ora,

>sqlnet.ora and tnsnames.ora files

>   server = shared

>   server = dedicated

>

>The results are still the same.

>I heard that the server process is single threaded, but

>I did set the mts_servers to N, I see the database started-up

>N ora_sxxxx_<i>dbname</i> processes.

>In addition for each connection I open I see that it spawn

>one oracle<i>dbname</i> process.  This seems to be the case

>whether I set the parameter for DEDICATED or MTS.

>I don't know which process is serializing the request.

>

>It's hard to believe that this is how it is supposed to behave,

>or is it ?  What do I need to do to improve this ?

>

>Thanks

>

>