SQL Query to Find Out Current Utilization of Redo Log in Oracle database

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This script calculates the utilization percentage of the redo log in the Oracle database. The redo log consists of multiple groups, and each group can have multiple log members (files). We use the V$LOG and V$LOGFILE views to obtain information about the redo log groups and their associated log members, respectively. The V$LOG view provides information about the redo log groups, and the V$LOGFILE view provides information about the log files associated with each group. The script then calculates the total size of each redo log group using the SUM(BYTES) function from the V$LOG view and stores the result in the RL (Redo Log) subquery. Next, we calculate the current redo log utilization by subtracting the available space (RL.BYTES) from the total size of the redo log group (LG.BYTES). The percentage of redo log utilization is then calculated by dividing the used space by the total space and multiplying by 100.

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In Oracle, the redo log is a crucial component of the database architecture that ensures data consistency and recovery in the event of a failure. When data changes occur in the database (e.g., INSERT, UPDATE, DELETE), Oracle records these changes in the redo log files before applying them to the actual data files. This process is known as the "write-ahead logging" mechanism. The redo log is organized into redo log groups, and each group consists of one or more log members (physical log files). The redo log groups are used in a circular fashion, and when the active redo log group is filled, the next group becomes active, and so on. The database continues to switch between redo log groups in a circular manner. The redo log utilization percentage is an important metric to monitor because if the redo log space is exhausted, it can cause the database to halt, leading to downtime and potential data loss. It is essential to ensure that there is enough redo log space available to handle the database workload and prevent issues like "ORA-01653: unable to extend table" or "ORA-00257: archiver error." Monitoring the redo log utilization percentage helps database administrators to proactively manage the database's performance and storage needs. Regularly checking the redo log space and making appropriate adjustments to the redo log file size or the number of redo log groups can help ensure the smooth functioning of the Oracle database. 

 Query 1

SELECT
  (1 - (LG.BYTES - RL.BYTES) / LG.BYTES) * 100 AS redo_log_utilization_percent
FROM
  V$LOG LG,
  V$LOGFILE LF,
  (SELECT GROUP#, SUM(BYTES) BYTES FROM V$LOG GROUP BY GROUP#) RL
WHERE
  LG.GROUP# = LF.GROUP#
  AND LG.GROUP# = RL.GROUP#;

REDO_LOG_UTILIZATION_PERCENT
----------------------------
15.62

Query 2 

 The SQL query you provided utilizes the X$KCCCP and X$KCCLE dynamic performance views to retrieve information about the redo log groups and calculate the current redo log utilization percentage. Instead of using the V$LOG and V$LOGFILE views, you can use the X$KCCCP and X$KCCLE dynamic performance views to get information about the redo log groups and log members. Here's the rewritten SQL query using X$KCCCP and X$KCCLE:

 

SELECT
  le.leseq "Current log sequence No",
  100 * cp.cpodr_bno / le.lesiz "Percent Full",
  cp.cpodr_bno "Current Block No",
  le.lesiz "Size of Log in Blocks"
FROM
  x$kcccp cp,
  x$kccle le
WHERE
  le.leseq = cp.cpodr_seq
  AND bitand(le.leflg, 24) = 8;

Query Output

Current log sequence No | Percent Full | Current Block No | Size of Log in Blocks
----------------------- | ------------ | ---------------- | ---------------------
102                     | 34.72        | 225              | 648

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