Before-Image Fies

Before image file

Before image file is a file which store the transaction information (like user, transaction number and previous value) happens in the DB in a Binary form, once the transaction is completed it will stores the binary info on how to modify the records and indices. if the transaction is aborted then DB will reads the data from the bi file and stores in it.

BI files are essential to access any DB. At least one BI and one data file is required.

BI in .st file,

            BI entry in a .st is file must, a simple entry can be made as below

b .

            b here is stands for the before image file and “.” stands for the current directory where DB is going to create.

It will be good practice to have as much bi file is needed, when the long running transaction happening it will keep on writing the transaction details to the bi files which leads to growth in bi file, when bi growth is occur which may affects the performance or once it reaches the maximum size then which may down the DB as well!. so it is must to keep an eye on the BI file size.

           

            It is always a good practice to run one Before-image page Writer (BIW) for Database to reduce the Bottleneck happen from BI.

Syntax: probiw <db-name>

Ultimately you can have only one biw per DB which consumes one “–n”

           

How to check the size of the BI?

You can find the current size of bi

 for each  _dbstatus no-lock.

  disp (_dbstatus-bisize  *  _DbStatus-BiBlkSize / 1048576  ) format   ">>>,>>>,>>>,>>9"  label "BI Size#"

    ( _DBStatus-BISize * _DBStatus-DBBlkSize / 1048576 ) format ">>>,>>>,>>>,>>9"   label "Used BI Size#"  with frame bi.

But remember this query will give you the actual size of bi once it crosses bi cluster 

Monitoring BI Activity

Use operating system utilities to monitor the amount of I/O activity on the disk where the BI file or files reside. Use the PROMON utility to monitor specific BI activity. Use the R&D option BI Log Activity -

promon > R&D > 2. Activity Displays > 5. BI Log

- Busy buffer waits

- Empty buffer waits

- High number of writes per second

- High number of partial writes

How to Truncate the Grown Bi Size

            Shutdown th DB using proshut or promon

            Hit the below command

proutil <db-name> -C truncate bi