数据库redolog切换频率统计分析

redolog切换频率分析，一方面可以辅助评估数据库运行的繁忙程度，得出数据库忙闲时段的具体分布，另一方面结合redolog的大小可以评估开启归档所需预留的磁盘空间。下面分享笔者使用的一条sql语句，使用该语句可以得出redolog的切换频率分布结果。SELECT TRUNC (first_time) "Date", TO_CHAR (first_time, 'Dy') "Day", COUNT (1) "Total", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '00', 1, 0)) h0, SUM (DECODE (TO_CHAR (first_time, 'hh24'), '01', 1, 0)) "h1", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '02', 1, 0)) "h2", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '03', 1, 0)) "h3", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '04', 1, 0)) "h4", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '05', 1, 0)) "h5", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '06', 1, 0)) "h6", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '07', 1, 0)) "h7", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '08', 1, 0)) "h8", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '09', 1, 0)) "h9", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '10', 1, 0)) "h10", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '11', 1, 0)) "h11", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '12', 1, 0)) "h12", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '13', 1, 0)) "h13", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '14', 1, 0)) "h14", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '15', 1, 0)) "h15", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '16', 1, 0)) "h16", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '17', 1, 0)) "h17", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '18', 1, 0)) "h18", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '19', 1, 0)) "h19", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '20', 1, 0)) "h20", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '21', 1, 0)) "h21", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '22', 1, 0)) "h22", SUM (DECODE (TO_CHAR (first_time, 'hh24'), '23', 1, 0)) "h23", to_char(ROUND (COUNT (1) / 24, 2),'fm99999999990.00') "Avg" FROM gv$log_history WHERE first_time >= trunc(SYSDATE) - 30 and thread# = inst_id GROUP BY TRUNC (first_time), TO_CHAR (first_time, 'Dy') ORDER BY 1 DESC; 使用toad的Log Switch Frequency Map功能也可以直接统计出切换热图，结果如下：