Oracle - Explain the purpose of DBFile Sequential and Scattered Reads. posted
by Babu Kunwar
Explain the purpose of DBFile Sequential and Scattered Reads.
DBFile: DB_FILES is the maximum number of datafiles that can be
opened for a database.
DBFile Sequential Read is a single-block read which indicates
that user process is reading a buffer into the SGA buffer cache and is waiting
for a physical I/O read request to complete. It basically has three parameters
namely file#, first block#, and block count. It is initiated by SQL statements
that perform single-block read operations against indexes, rollback segments,
and tables, control files and data file headers. Remember: Physical I/O
requests for these objects are perfectly normal, so the presence of the db file
sequential read waits in the database does not necessarily mean that there is
something wrong with the database or the application. It may not even be a bad
thing if a session spends a lot of time on this event.
DBFile Scattered Read: The db file scattered read wait event
same as db file sequential read event but the only difference is that it is
multiblock read. It also has the same four parameters as sequential read. It
reads the data and distributes them into different buffers in SGA. It indicates
the disk argument in the case of the full table scan.
More links
What are PL/SQL Subprograms?
Advantages of PL/SQL Subprograms.
PL/SQL has two types of subprograms called procedures and functions. Explain
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parameters? Explain with an example
Define three parameter modes, IN (the default), OUT, and IN OUT that can be
used with any subprogram.............
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