How do I fix a scattered read database?
The cure for the db file scattered read waits is the same as the one for the db file sequential read: find and tune the SQL statement that clocked the most time on the event. The goal of tuning is also to minimize the number of logical and physical I/Os. Follow the examples in the db file sequential read event section.
What is the difference between db file sequential and scattered reads?
A db file sequential read is an event that shows a wait for a foreground process while doing a sequential read from the database. 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.
What is db file parallel read?
The db file parallel read Oracle metric occurs when the process has issued multiple I/O requests in parallel to read blocks from data files into memory, and is waiting for all requests to complete.
What is db file sequential read in Oracle?
In simple words, Db file sequential reads wait event occurs when a process has issued an I/O request to read one block (single block I/O) from a datafile (Or datafile headers) into the buffer cache and is waiting for the operation to complete.
How do I resolve log file sync wait event?
The Oracle “log file sync” wait event is triggered when a user session issues a commit (or a rollback)….If slow I/O, investigate the following:
- Reduce contention on existing disks.
- Put log files on faster disks.
- Put alternate redo logs on different disks to minimize the effect archive processes (log files switches).
What is direct path read in Oracle?
A direct read is a physical I/O from a data file that bypasses the buffer cache and reads the data block directly into process-private memory. If asynchronous I/O is supported (and in use), then Oracle can submit I/O requests and continue processing.
What causes log file sync waits?
The Oracle “log file sync” wait event is triggered when a user session issues a commit (or a rollback). The user session will signal or post the LGWR to write the log buffer to the redo log file. When the LGWR has finished writing, it will post the user session.
What is direct path read temp in Oracle?
The Direct Path Read Temp wait events are an access path in which multiple Oracle blocks are read directly to the Oracle process memory without being read into the buffer cache in the Shared Global Area (SGA). in Direct Path Read Temp the data is read from temporary tablespaces.