There are several background processes running when you start Oracle Database 12c instance. Here is an example from one of the 12.1.0.2 instances.
|
ora_acms_bt9prod1 |
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). |