Multiprocess and Multithreaded Oracle Database

Multithreaded Configuration

A process is a mechanism in an operating system that can run a series of steps. The process execution architecture depends on the operating system. For example, on Windows an Oracle background process is a thread of execution within a process. On Linux and UNIX, an Oracle process is either an operating system process or a thread within an operating system process.

Types of Processes

A database instance contains or interacts with the following types of processes:

·         A client process runs the application or Oracle tool code.

·         An Oracle process is a unit of execution that runs the Oracle database code. In the multithreaded architecture, an Oracle process can be an operating system process or a thread within an operating system process. Oracle processes include the following subtypes:

·         A background process starts with the database instance and perform maintenance tasks such as performing instance recovery, cleaning up processes, writing redo buffers to disk, and so on.

·         A server process performs work based on a client request.

Oracle database running on Linux uses the same architecture and every process like LGWR, DBWR, SMON has it’s own OS processes. The resources consumed are visible in OS level process monitoring tools.Oracle 12c database has the same architecture. The below command was run on fresh install of 12c database.

ps -ef | grep [o]ra_

oracle 2191 1 0 06:07 ? 00:00:00 ora_pmon_cdb12c
oracle 2193 1 0 06:07 ? 00:00:00 ora_psp0_cdb12c
oracle 2195 1 31 06:07 ? 00:00:20 ora_vktm_cdb12c
oracle 2199 1 0 06:07 ? 00:00:00 ora_gen0_cdb12c
oracle 2201 1 0 06:07 ? 00:00:00 ora_mman_cdb12c
oracle 2205 1 0 06:07 ? 00:00:00 ora_diag_cdb12c
oracle 2207 1 0 06:07 ? 00:00:00 ora_dbrm_cdb12c
oracle 2209 1 0 06:07 ? 00:00:00 ora_dia0_cdb12c
oracle 2211 1 0 06:07 ? 00:00:00 ora_dbw0_cdb12c
oracle 2213 1 0 06:07 ? 00:00:00 ora_lgwr_cdb12c
oracle 2215 1 0 06:07 ? 00:00:00 ora_ckpt_cdb12c
oracle 2217 1 0 06:07 ? 00:00:00 ora_smon_cdb12c
oracle 2219 1 0 06:07 ? 00:00:00 ora_reco_cdb12c
oracle 2221 1 0 06:07 ? 00:00:00 ora_lreg_cdb12c
oracle 2223 1 5 06:07 ? 00:00:03 ora_mmon_cdb12c
oracle 2225 1 0 06:07 ? 00:00:00 ora_mmnl_cdb12c
oracle 2227 1 0 06:07 ? 00:00:00 ora_d000_cdb12c
oracle 2229 1 0 06:07 ? 00:00:00 ora_s000_cdb12c
oracle 2241 1 0 06:07 ? 00:00:00 ora_tmon_cdb12c
oracle 2243 1 0 06:07 ? 00:00:00 ora_tt00_cdb12c
oracle 2245 1 0 06:07 ? 00:00:00 ora_smco_cdb12c
oracle 2247 1 0 06:07 ? 00:00:00 ora_aqpc_cdb12c
oracle 2266 1 0 06:07 ? 00:00:00 ora_w000_cdb12c
oracle 2270 1 6 06:07 ? 00:00:03 ora_p000_cdb12c
oracle 2272 1 6 06:07 ? 00:00:03 ora_p001_cdb12c
oracle 2274 1 0 06:07 ? 00:00:00 ora_p002_cdb12c
oracle 2276 1 0 06:07 ? 00:00:00 ora_p003_cdb12c
oracle 2279 1 0 06:07 ? 00:00:00 ora_qm02_cdb12c
oracle 2283 1 0 06:07 ? 00:00:00 ora_q002_cdb12c
oracle 2285 1 0 06:07 ? 00:00:00 ora_q003_cdb12c
oracle 2309 1 0 06:07 ? 00:00:00 ora_p004_cdb12c
oracle 2311 1 1 06:07 ? 00:00:00 ora_p005_cdb12c
oracle 2329 1 5 06:08 ? 00:00:01 ora_cjq0_cdb12c
oracle 2333 1 2 06:08 ? 00:00:00 ora_p006_cdb12c
oracle 2335 1 2 06:08 ? 00:00:00 ora_p007_cdb12c
oracle 2338 1 0 06:08 ? 00:00:00 ora_vkrm_cdb12c
oracle 2346 1 0 06:08 ? 00:00:00 ora_p008_cdb12c
oracle 2348 1 0 06:08 ? 00:00:00 ora_p009_cdb12c
oracle 2350 1 0 06:08 ? 00:00:00 ora_p00a_cdb12c
oracle 2352 1 0 06:08 ? 00:00:00 ora_p00b_cdb12c
oracle 2354 1 2 06:08 ? 00:00:00 ora_j000_cdb12c
oracle 2356 1 4 06:08 ? 00:00:00 ora_j001_cdb12c
oracle 2358 1 1 06:08 ? 00:00:00 ora_j002_cdb12c
oracle 2360 1 2 06:08 ? 00:00:00 ora_j003_cdb12c
oracle 2362 1 3 06:08 ? 00:00:00 ora_j004_cdb12c
oracle 2364 1 2 06:08 ? 00:00:00 ora_j005_cdb12c
oracle 2366 1 2 06:08 ? 00:00:00 ora_j006_cdb12c
oracle 2368 1 3 06:08 ? 00:00:00 ora_j007_cdb12c
oracle 2370 1 1 06:08 ? 00:00:00 ora_j008_cdb12c
oracle 2372 1 2 06:08 ? 00:00:00 ora_j009_cdb12c
oracle 2374 1 1 06:08 ? 00:00:00 ora_j010_cdb12c
oracle 2376 1 1 06:08 ? 00:00:00 ora_j011_cdb12c
oracle 2378 1 2 06:08 ? 00:00:00 ora_j012_cdb12c
oracle 2380 1 2 06:08 ? 00:00:00 ora_j013_cdb12c
oracle 2382 1 1 06:08 ? 00:00:00 ora_j014_cdb12c
oracle 2384 1 3 06:08 ? 00:00:00 ora_j015_cdb12c
oracle 2386 1 1 06:08 ? 00:00:00 ora_j016_cdb12c
oracle 2388 1 1 06:08 ? 00:00:00 ora_j017_cdb12c
oracle 2390 1 2 06:08 ? 00:00:00 ora_j018_cdb12c
oracle 2392 1 1 06:08 ? 00:00:00 ora_j019_cdb12c
oracle 2394 1 1 06:08 ? 00:00:00 ora_j020_cdb12c
oracle 2396 1 0 06:08 ? 00:00:00 ora_j021_cdb12c
oracle 2398 1 5 06:08 ? 00:00:00 ora_m000_cdb12c

$ ps -ef | grep [o]ra_|wc
40 320 2560

Multithreaded Configuration

Starting in Oracle 12c database, you can change this and enable the new Multithreaded configuration. You can change the architecture by making Oracle database use thread based architecture instead of process based. Once changed, all Oracle processes will be threads within a few Oracle processes. Thus if CPU moves from one Oracle process to the other, the time between the context switch will be reduced significantly as the switching from one thread to the other is within the same process. During testing, this has resulted in up to 30% performance improvements. You can use the following command in SQL*PLUS to view the current value of THREADED_EXECUTION parameter.

The choice of threading model is dictated by the THREADED_EXECUTION initialization parameter.

THREADED_EXECUTION=FALSE : The default value causes Oracle to run using the multiprocess model.

THREADED_EXECUTION=TRUE : Oracle runs with the multithreaded model.

To switch to the multithreaded model, simply set the THREADED_EXECUTION parameter and restart the database.

CONN sys AS SYSDBA

ALTER SYSTEM SET threaded_execution=TRUE SCOPE=SPFILE;

SHUTDOWN IMMEDIATE;

STARTUP;

If you encounter “ORA-01017: invalid username/password; logon denied” while restarting database then please refer to the end of this article under OS Authentication.

SQL> SHOW PARAMETER thread;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
parallel_threads_per_cpu integer 2
thread integer 0
threaded_execution boolean TRUE

Also for all incoming requests to make use of this architecture you need to set the below mentioned parameter in Listener.ora file.

DEDICATED_THROUGH_BROKER_<listener-name>=ON

You need to provide your own Listener name at the end.

Now we will run the OS command again to check how many processes are created.

$ ps -ef | grep [o]ra_
oracle 2544 1 0 06:25 ? 00:00:00 ora_pmon_cdb12c
oracle 2546 1 0 06:25 ? 00:00:00 ora_psp0_cdb12c
oracle 2548 1 25 06:25 ? 00:01:47 ora_vktm_cdb12c
oracle 2552 1 0 06:25 ? 00:00:01 ora_u004_cdb12c
oracle 2558 1 9 06:25 ? 00:00:41 ora_u005_cdb12c
oracle 2564 1 0 06:25 ? 00:00:00 ora_dbw0_cdb12c

$ ps -ef | grep [o]ra_|wc
6 48 384

The number of processes have been reduced from 40 to 6. That is a huge plus and that’s because there isn’t a separate process for every Oracle process. Most of the Oracle processes are now threads within these 6 processes.

OS Authentication

When you enable Multithreaded configuration then you are not allowed to log into Oracle using OS level authentication. The following error will occur if you try to.

$ sqlplus / as sysdba
SQL*Plus: Release 12.1.0.1.0 Production on Sat Jul 6 06:40:39 2013
Copyright (c) 1982, 2013, Oracle. All rights reserved.
ERROR:
ORA-01017: invalid username/password; logon denied

Use the following method to log in as SYS.

Enter user-name: sys as sysdba
Enter password:
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options.