Higher bitmap switches recorded than scheduled incremental backup causing no use of BCT by cumulative backups
Last updated on MAY 30, 2016
Applies to:Oracle Database - Enterprise Edition - Version 126.96.36.199.0 and later
Information in this document applies to any platform.
Every incremental backups do BCT switches (recorded per datafile). By default Oracle keeps details of 8 incremental backups . If need to store more bitmaps (number of incremental backups higher than 8 in b/w 2 L0 backups) then need to adjust by parameter "_bct_bitmaps_per_file" (default 8) accordingly so that BCT file having sufficient history to use BCT .
We can keep track of these bitmaps and incremental backups via below query (query tweaked for one datafile you can remove the file number to get datails of all the files)
set linesize 400
set pagesize 100
set numwidth 16
Select RECID, FILE#, CREATION_CHANGE#, CREATION_TIME, INCREMENTAL_LEVEL,INCREMENTAL_CHANGE#, CHECKPOINT_CHANGE#, CHECKPOINT_TIME, MARKED_CORRUPT,USED_CHANGE_TRACKING FROM v$backup_datafile where file#=<file number>;
SELECT inst_id, csno, fno, vercnt, vertime, hist_first, hist_last, low, high FROM x$krcfbh where fno=<file number> ORDER BY csno, fno, vercnt;
Some times we see incremental backups not using BCT and same time we see more bitmap switches than expected ( switch count (bitmap version) should be equal to number of incremental backups)
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