So, I have several questions about this wait event. db file sequential read; db file scattered read; direct path read; direct path read temp; direct path write temp; free buffer wait; log file sync; read by other session; In the next few posts, I will explain these waits. Time is reported in100's of a second for Oracle8i releases and below, and1000's of a second for Oracle9i and above. Database blocks that must be changed as part of recovery are read in parallel from the database. Oracle issues single-block I/O read requests when reading from indexes, rollback segments, sort segments, controlfiles, datafile headers and … The db file sequential read is thus named because it reads blocks into contiguous memory from the segment involved. Wait Time: Wait until all of the I/Os are completed. The table is indexed. An Oracle session logs the db file sequential read wait event when it has to wait for a single-block I/O read request to complete. This important information is taken from the Oracle performance white paper written by Bartal Vindzberg. Most people confuse these events with each other as they think of how data is read from disk. Instead they should think of how data is read into the SGA buffer cache or user … This happens during recovery. Parameter Description; files. C.3.34 db file parallel read. Firstly, when I encounter this event when inserting. It can also happen during buffer prefetching, as an optimization (rather than performing multiple single-block reads). I thought it was illogical. Both "db file sequential read" and "db file scattered read" events signify time waited for I/O read requests to complete. Most people confuse these events with each other as they think of how data is read from disk. This wait may also be seen for reads from datafile headers (P2=1 indicates a file header read… You will find that the object is normally an index or a table. A sequential read is usually a single-block read, although it is possible to see sequential reads for more than one block (See P3). db file sequential read event happen when inserting on ordinary heap table (This is log table).

The db file sequential read “System-Level Diagnosis” section has some ideas on how to improve the AVERAGE_WAIT time.

As you monitor a session and come across the db file sequential read event, you should translate its P1 and P2 parameters into the object that they represent. It didn't make any sense because I am not selecting from table I am inserting to table. Physical I/O requests for index blocks are perfectly normal and so the presence of the db file sequential read waits do not necessarily mean that there is something wrong with the database or the application.

Time is reported in 100's of a second for Oracle 8i releases and below, and 1000's of a second for Oracle 9i and above. Both "db file sequential read" and "db file scattered read" events signify time waited for I/O read requests to complete.



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