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    Strategies for using BLOB functions in Voyager Prepackaged Access Reports

    • Product: Voyager
    • Relevant for Installation Type: Multi-Tenant Direct, Dedicated-Direct, Local, TotalCare

     

    Question

    What are some strategies for using the BLOB functions in Prepackaged Access Reports?

    Answer

    The BLOB functions (GetBibBlob, GetFieldRaw, GetSubField, etc.) are priceless for people who write queries against a Voyager database, because they often provide the only way to get at data in certain MARC fields. But if you have a large database and if you don’t use the BLOB functions wisely, you can easily create reports that run for hours.

    The reason the BLOB functions are slow is this: They are implemented in Access on your workstation. If you use a BLOB function on, say, all the bib records in your database, then all of the bib records have to be brought across the network to your workstation, and then parsed out by your workstation. Today’s workstations are powerful computing machines, but parsing MARC records is an intensive task and and the data transfer processing is highly susceptible to network vagaries. 

    Here are a few strategies for using the BLOB functions:

    • One strategy is to make sure you really need to use the BLOB functions.  See: Alternatives to BLOB queries in Voyager Prepackaged Access Reports
    • Another is to use the BLOB functions on the smallest set of records that will still let your query accomplish what you need to do.  In other words, create the shortest possible list of BIB_IDs, MFHD_IDs or AUTH_IDs on which the BLOB function will be used.  A good way to do this use a Make Table query.
    • A third is to avoid putting criteria on a column that is created by BLOB functions. When you use criteria, Access is going to get all of the records in your database, bring them to your workstation, and parse them all there to see if they meet the criterion you have specified.

    See also: How do I find records with a specific MARC field in the database? for alternatives to using Prepackaged Access Reports (such as Global Data Change) for finding records with specific MARC fields in the database.

    Additional Information

    BLOB stands for Binary Large OBject.  The whole MARC records is stored as a Binary Large OBject and the BLOB functions allow you to get at any piece of the MARC record.

    Constructing custom SQL queries by request and troubleshooting unexpected results from customer-created SQL queries falls outside the scope of Support. The above has been posted for informational purposes.  Voyager-L and Developer Network are useful resources for finding helpful custom SQL or obtaining assistance from peers in troubleshooting custom queries.


    • Article last edited: 02-Jun-2020