What is buffer busy waits in Oracle?
The buffer busy wait event happens when a session tries to access a block in the buffer cache but it can’t because the buffer is busy, because another session is modifying the block and the contents of the block are in flux. Another session holds the buffer in an incompatible mode to our request.
What is sequential read in SAP?
A “Sequential Read” refers to all other read database accesses, in which there may be more than one line returned. It is true that the term “Sequential read” is a little deceptive since it implies that blocks are always read sequentially (as in a full table scan).
What is db file scattered read?
For scan operations (index range scans, index fast full scans, and full-table scans), a read-ahead cache can be very useful for speeding up these “scattered read” operations. In sum, if your database is requesting adjacent data blocks, the read-ahead cache may improve I/O throughput.
What is db file parallel read in Oracle?
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.
How do you reduce buffer busy waits?
The main way to reduce buffer busy waits is to reduce the total I/O on the system. This can be done by tuning the SQL to access rows with fewer block reads (i.e., by adding indexes). Even if we have a huge db_cache_size, we may still see buffer busy waits, and increasing the buffer size won’t help.
What is GC buffer busy acquire?
C. 3.16 buffer busy waits Wait until a buffer becomes available. “gc buffer busy acquire”: A session cannot pin the buffer in the buffer cache because another session is reading the buffer from the cache of another instance.
What do Db_file_sequential_read and db file scattered read event define?
A db file scattered read issues a scattered read to read the data into multiple discontinuous memory locations. A scattered read is usually a multiblock read. It can occur for a fast full scan (of an index) in addition to a full table scan. The db file scattered read wait event identifies that a full scan is occurring.