How do you avoid db file sequential read waits?
There are two things you can do to minimize the db file sequential read waits:
- Optimize the SQL statement that initiated most of the waits by reducing the number of physical and logical reads.
- Reduce the average wait time.
What is the difference between PGA aggregate limit and Pga_aggregate_target?
By default, PGA_AGGREGATE_LIMIT is set to the greater of 2 GB, 200% of PGA_AGGREGATE_TARGET , and 3 MB times the PROCESSES parameter. It will be set below 200% of PGA_AGGREGATE_TARGET if it is larger than 90% of the physical memory size minus the total SGA size, but not below 100% of PGA_AGGREGATE_TARGET .
What is sequential write and scattered write in Oracle?
A db file scattered read is the same type of event as “db file sequential read”, except that Oracle will read multiple data blocks. Multi-block reads are typically used on full table scans.
How many types of wait events are there in Oracle?
Long before Oracle Database 10g, DBAs have been classifying wait events into four main categories: Foreground, Background, Idle, and Non-Idle events. Foreground events are posted by sessions that have V$SESSION.
What is Oracle Wait Event?
File Open—This wait event happens when the database needs to open a file. Wait time is recorded starting just prior to when the open request is issued and extends until the time the request is returned, having succeeded or failed, from the operating system.
What causes db file sequential read?
The db file sequential read event signifies that the user process is reading data into the SGA buffer cache and is waiting for a physical I/O call to return. It corresponds to a single-block read. Single block I/Os are usually the result of using indexes.
What is scattered write?
scattered write means that you’re writing from each cuda thread to an arbitrary address (ie. the threads of your warp will not write in consecutive memory, e.g.). It contrasts with frame-buffer writes, which are 2d-coherent, and can be coalesced by the hardware.
What is wait event?
Wait events are statistics that a server process or thread increments when it waits for an operation to complete in order to continue its processing. For example, a SQL statement may be modifying data, but the server process may have to wait for a data block to be read from disk because it’s not available in the SGA.