資料庫redolog切換頻率統計分析

redolog切換頻率分析，一方面可以輔助評估資料庫執行的繁忙程度，得出資料庫忙閒時段的具體分佈，另一方面結合redolog的大小可以評估開啟歸檔所需預留的磁碟空間。下面分享筆者使用的一條sql語句，使用該語句可以得出redolog的切換頻率分佈結果。

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功能也可以直接統計出切換熱圖，結果如下：