DBWn与物理写

数据库的物理写，主要有针对数据文件、日志文件和归档日志文件，下面我们讨论针对数据文件的物理写。
数据文件的物理写主要由DBWn进程完成。如果DBWn写的缓慢了，我们可以从2个等待事件上看到这点。一个是db file parallel write,直译就是数据文件并行写 。DBWn在写脏块到磁盘数据文件中时，如果写操作的完成时间超过了1微妙(us，百万分之一秒)，就会记入这个等待事件。
show parameter db_write
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------

db_writer_processes integer 1
写进程的数量
ps -ef | grep ora_
oracle 2587 1 0 14:34 ? 00:00:01 ora_pmon_orcl
oracle 2589 1 0 14:34 ? 00:00:04 ora_psp0_orcl
oracle 2591 1 0 14:34 ? 00:00:07 ora_vktm_orcl
oracle 2595 1 0 14:34 ? 00:00:00 ora_gen0_orcl
oracle 2597 1 0 14:34 ? 00:00:00 ora_diag_orcl
oracle 2599 1 0 14:34 ? 00:00:00 ora_dbrm_orcl
oracle 2601 1 0 14:34 ? 00:00:04 ora_dia0_orcl
oracle 2603 1 0 14:34 ? 00:00:01 ora_mman_orcl
oracle 2605 1 0 14:34 ? 00:00:02 ora_dbw0_orcl
oracle 2607 1 0 14:34 ? 00:00:03 ora_lgwr_orcl
oracle 2609 1 0 14:34 ? 00:00:04 ora_ckpt_orcl
oracle 2611 1 0 14:34 ? 00:00:03 ora_smon_orcl
oracle 2613 1 0 14:34 ? 00:00:00 ora_reco_orcl
oracle 2615 1 0 14:34 ? 00:00:03 ora_mmon_orcl
oracle 2617 1 0 14:34 ? 00:00:04 ora_mmnl_orcl
oracle 2619 1 0 14:34 ? 00:00:00 ora_d000_orcl
oracle 2621 1 0 14:34 ? 00:00:00 ora_s000_orcl
oracle 2691 1 0 14:35 ? 00:00:00 ora_qmnc_orcl
oracle 2807 1 0 14:35 ? 00:00:03 ora_cjq0_orcl
oracle 2809 1 0 14:35 ? 00:00:00 ora_q000_orcl
oracle 2811 1 0 14:35 ? 00:00:00 ora_q001_orcl
oracle 3287 1 0 14:40 ? 00:00:00 ora_smco_orcl
oracle 8179 1 0 19:00 ? 00:00:00 ora_w001_orcl
oracle 8514 1 0 19:20 ? 00:00:00 ora_j000_orcl
oracle 8516 1 0 19:20 ? 00:00:00 ora_j001_orclps -ef | grep ora_
oracle 2587 1 0 14:34 ? 00:00:01 ora_pmon_orcl
oracle 2589 1 0 14:34 ? 00:00:04 ora_psp0_orcl
oracle 2591 1 0 14:34 ? 00:00:07 ora_vktm_orcl
oracle 2595 1 0 14:34 ? 00:00:00 ora_gen0_orcl
oracle 2597 1 0 14:34 ? 00:00:00 ora_diag_orcl
oracle 2599 1 0 14:34 ? 00:00:00 ora_dbrm_orcl
oracle 2601 1 0 14:34 ? 00:00:04 ora_dia0_orcl
oracle 2603 1 0 14:34 ? 00:00:01 ora_mman_orcl
oracle 2605 1 0 14:34 ? 00:00:02 ora_dbw0_orcl
oracle 2607 1 0 14:34 ? 00:00:03 ora_lgwr_orcl
oracle 2609 1 0 14:34 ? 00:00:04 ora_ckpt_orcl
oracle 2611 1 0 14:34 ? 00:00:03 ora_smon_orcl
oracle 2613 1 0 14:34 ? 00:00:00 ora_reco_orcl
oracle 2615 1 0 14:34 ? 00:00:03 ora_mmon_orcl
oracle 2617 1 0 14:34 ? 00:00:04 ora_mmnl_orcl
oracle 2619 1 0 14:34 ? 00:00:00 ora_d000_orcl
oracle 2621 1 0 14:34 ? 00:00:00 ora_s000_orcl
oracle 2691 1 0 14:35 ? 00:00:00 ora_qmnc_orcl
oracle 2807 1 0 14:35 ? 00:00:03 ora_cjq0_orcl
oracle 2809 1 0 14:35 ? 00:00:00 ora_q000_orcl
oracle 2811 1 0 14:35 ? 00:00:00 ora_q001_orcl
oracle 3287 1 0 14:40 ? 00:00:00 ora_smco_orcl
oracle 8179 1 0 19:00 ? 00:00:00 ora_w001_orcl
oracle 8514 1 0 19:20 ? 00:00:00 ora_j000_orcl
oracle 8516 1 0 19:20 ? 00:00:00 ora_j001_orcl
oracle 8528 3631 0 19:20 pts/2 00:00:00 grep ora_oracle 8528 3631 0 19:20 pts/2 00:00:00 grep ora_
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