Skip to Content
avatar image
Former Member

IQ fractured/torn blocks

Hi all,

I asked the question to SAP support, and they pointed me to the IQ SCN.

My question is:

How does IQ prevents fractured/torn blocks on disk in the case a server crashes in the middle of a block write ?

Is the IQ checkpoint log used for this purpose (double write) and what exactly gets written into the IQ checkpoint log ?

Thanks in advance for your answers,

Marco

Add comment
10|10000 characters needed characters exceeded

  • Get RSS Feed

1 Answer

  • avatar image
    Former Member
    Oct 09, 2015 at 01:27 PM

    Hi Marco,

        Can you please clarify on your question? IQ have two distinct storage , on is IQ data storage which stores IQ main data and IQ catalog database, which stores IQ meta data. IQ by nature of design is non-transactional server. The .log file contains information for catalog database to be consistent. IQ main data store is accessed by many threads which executes synchronous write to the disk. For this very reason, we do recommend to use raw devices for IQ main store rather than File-system device.

       Is your question relates some how to comparison between IQ and ASE?

    Regards

    Shashi

    Add comment
    10|10000 characters needed characters exceeded

    • Former Member Mark Mumy

      Mark,

      To answer your question, I never see a high number of C blocks. When I execute the sp_iqdbspace procedure I see a few blocks of type C. They disappear and come again. I was just wondering what was their use.

      From your post I understand that the C blocks contains the IQ internal transaction log that is located on the IQ main store.

      I have found this paragraph in the IQ manuals:

      CREATE DATABASE Statement

        Warning!  IQ_SYSTEM_MAIN is a special dbspace that contains all structures necessary for the database to open:

        the IQ db_identity blocks,

        the IQ checkpoint log,

        the IQ rollforward/rollback bitmaps of each committed transaction and each active checkpointed transaction,

        the incremental backup bitmaps,

        and the freelist root pages.

      The way I understand it is that the transaction log (IQ rollforward/rollback bitmaps) and the checkpoint log were 2 different things, both located on the IQ Store. Modifying the transaction log(IQ rollforward/rollback bitmaps) generates entries in the checkpoint log. Only when the entries in the IQ internal transaction log are removed, are the corresponding entries in the checkpoint log removed as well (seems to happen when a transaction is APPLIED). Both the IQ internal transaction log and the checkpoint log are used to recover the IQ store.  I am correct ?

      Thanks for your help.

      Marco