Critical Background Processes in Oracle Database 12c

There are several background processes running when you start Oracle Database 12c instance. Here is an example from one of the instances.



 ora_lreg_bt9prod1 ora_p00w_bt9prod1
 ora_aqpc_bt9prod1  ora_m000_bt9prod1  ora_p00x_bt9prod1
 ora_asmb_bt9prod1  ora_mark_bt9prod1  ora_p00y_bt9prod1
 ora_cjq0_bt9prod1  ora_mman_bt9prod1  ora_p00z_bt9prod1
 ora_ckpt_bt9prod1  ora_mmnl_bt9prod1  ora_ping_bt9prod1
 ora_dbrm_bt9prod1  ora_mmon_bt9prod1  ora_pmon_bt9prod1
 ora_dbw0_bt9prod1  ora_o000_bt9prod1  ora_ppa6_bt9prod1
 ora_dbw1_bt9prod1  ora_p000_bt9prod1  ora_ppa7_bt9prod1
 ora_dbw2_bt9prod1  ora_p001_bt9prod1  ora_psp0_bt9prod1
 ora_dbw3_bt9prod1  ora_p002_bt9prod1  ora_pxmn_bt9prod1
 ora_dbw4_bt9prod1  ora_p003_bt9prod1  ora_q001_bt9prod1
 ora_dbw5_bt9prod1  ora_p004_bt9prod1  ora_q003_bt9prod1
 ora_dbw6_bt9prod1  ora_p005_bt9prod1  ora_q006_bt9prod1
 ora_dbw7_bt9prod1  ora_p006_bt9prod1  ora_q008_bt9prod1
 ora_dbw8_bt9prod1  ora_p007_bt9prod1  ora_q009_bt9prod1
 ora_dbw9_bt9prod1  ora_p008_bt9prod1  ora_q00a_bt9prod1
 ora_dbwa_bt9prod1  ora_p009_bt9prod1  ora_q00b_bt9prod1
 ora_dbwb_bt9prod1  ora_p00a_bt9prod1  ora_qm00_bt9prod1
 ora_dbwc_bt9prod1  ora_p00b_bt9prod1  ora_qm02_bt9prod1
 ora_dbwd_bt9prod1  ora_p00c_bt9prod1  ora_qm03_bt9prod1
 ora_dbwe_bt9prod1  ora_p00d_bt9prod1  ora_qm05_bt9prod1
 ora_dbwf_bt9prod1  ora_p00e_bt9prod1  ora_rbal_bt9prod1
 ora_dia0_bt9prod1  ora_p00f_bt9prod1  ora_rcbg_bt9prod1
 ora_diag_bt9prod1  ora_p00g_bt9prod1  ora_reco_bt9prod1
 ora_gcr0_bt9prod1  ora_p00h_bt9prod1  ora_rms0_bt9prod1
 ora_gen0_bt9prod1  ora_p00i_bt9prod1  ora_rmv0_bt9prod1
 ora_gtx0_bt9prod1  ora_p00j_bt9prod1  ora_rmv1_bt9prod1
 ora_lck0_bt9prod1  ora_p00k_bt9prod1  ora_rmv2_bt9prod1
 ora_lck1_bt9prod1  ora_p00l_bt9prod1  ora_rsmn_bt9prod1
 ora_lg00_bt9prod1  ora_p00m_bt9prod1  ora_smco_bt9prod1
 ora_lg01_bt9prod1  ora_p00n_bt9prod1  ora_smon_bt9prod1
 ora_lgwr_bt9prod1  ora_p00o_bt9prod1  ora_tmon_bt9prod1
 ora_lmd0_bt9prod1  ora_p00p_bt9prod1  ora_tt00_bt9prod1
 ora_lmd1_bt9prod1  ora_p00q_bt9prod1  ora_vkrm_bt9prod1
 ora_lmhb_bt9prod1  ora_p00r_bt9prod1  ora_vktm_bt9prod1
 ora_lmon_bt9prod1  ora_p00s_bt9prod1  ora_w008_bt9prod1
 ora_lms0_bt9prod1  ora_p00t_bt9prod1  ora_w009_bt9prod1
 ora_lms1_bt9prod1  ora_p00u_bt9prod1  
 ora_lms2_bt9prod1  ora_p00v_bt9prod1  

Which processes are critical for database operation? In other words, if you terminate one of these processes knowingly or unknowingly, will the instance terminate?

The critical processes required for basic database operation are:

Acronym Process Name Description
CKPT Checkpoint Process Signals DBWn at checkpoints and updates all the data files and control files of the database to indicate the most recent checkpoint
DBWn Database Writer Process Writes modified blocks from the database buffer cache to the data files. There can be 1 to 100 Database Writer Processes. The names of the first 36 Database Writer Processes are DBW0-DBW9 and DBWa-DBWz. The names of the 37th through 100th Database Writer Processes are BW36-BW99.
BWnn Database Writer Process The names of the 37th through 100th Database Writer Processes are BW36-BW99.
DIAG Diagnostic Capture Process Performs diagnostic dumps and executes global oradebug commands.
DIA0 Diagnostic Process 0 (although 10 possible, only 0 is currently used) Responsible for hang detection and deadlock resolution. Triggers DIAG to perform diagnostic tasks.
GEN0 General Task Execution Process Performs required tasks including SQL and DML.
CSnn I/O Calibration Process Issues I/Os to storage as part of storage calibration. There is one slave process per CPU on each node of the database.
LREG Listener Registration Process LREG notifies the listeners about instances, services, handlers, and endpoint.
LGWR Log Writer Process Writes the log buffer out to the redo logs.
OFSD Oracle File Server Background Process This background process listens for new file system requests, both management (like mount, unmount, and export) and I/O requests, and executes them using Oracle threads.
PMON Process Monitor Recovers failed process resources. If Shared Server architecture is used, PMON monitors and restarts any failed dispatcher or server processes.
SMON System Monitor Process Performs critical tasks such as instance recovery and dead transaction recovery, and maintenance tasks such as temporary space reclamation, data dictionary cleanup, and undo tablespace management
VKTM Virtual Keeper of Time Process Responsible for providing a wall-clock time (updated every second) and reference-time counter (updated every 20ms and available only when running at elevated priority).


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