I would like to understand the mechanism of "How data is written to the IRIS Database and in what sequence data is written to Journal, WIJ and IRIS database"
I would like to understand the mechanism of "How data is written to the IRIS Database and in what sequence data is written to Journal, WIJ and IRIS database"
Comments
WIJ (write image journal) is used for data before it is saved to the database. This is used to keep the data consistency (block level in database) and avoid database degradation. If IRIS (or the OS) crash, WIJ will have "dirty blocks" (not written to databases) that will be weritten during the next IRIS startup.
Journal files (or mirror journal, in case you have mirroring) are used after data saved to the database. This will help for transactions rollback and also to ensure a good restore point up to the "current time" along with the latest backup restore.
The sequence is:
1. Read a block was changed from the database
2. Write the modified block to WIJ
3. Write the modified block to the database
4. Write the global SETS and KILLS (and also transaction start/stop) to the journal file