What are the best ways to reduce the number of logical reads?
Usually the best way to reduce logical read is to apply correct index or to rewrite the query. Physical read indicates total number of data pages that are read from disk. In case no data in data cache, the physical read will be equal to number of logical read. And usually it happens for first query request.
What is logical read in Oracle?
A logical read is a read request for a data block from the SGA. Logical reads may result in a physical read if the requested block does not reside with the buffer cache. This test checks the logical(db block gets + consistent gets) reads per second.
What is Lio in Oracle?
An Oracle LIO (or logical read call) occurs any time the Oracle kernel requests access to an Oracle block in the database buffer cache. The number of LIO calls for a session is the sum of the values in v$sesstat for the statistics named “db block gets” and “consistent gets.”
What is SQL Server logical IO?
A logical IO is a read of an 8K page from cache and a block is an 8k pages on disk. A single physical IO may be a single page read or multiple 64K extents (contiguous pages) using scatter-gather IO. The physical IO may be done via prefetch or when a need page isn’t already in cache. –
What is consistent gets in Oracle?
The consistent gets Oracle metric is the number of times a consistent read (a logical RAM buffer I/O) was requested to get data from a data block.
Why is the number of logical reads so high?
Logical read indicates total number of data pages needed to be accessed from data cache to process query. It is very possible that logical read will access same data pages many times, so count of logical read value may be higher than actual number of pages in a table.
Which is the best way to reduce logical read?
Usually the best way to reduce logical read is to apply correct index or to rewrite the query. Physical read indicates total number of data pages that are read from disk.
When does a logical read occur in a database?
A logical read occurs every time the database engine requests a page from the buffer cache. If the page is not currently in the buffer cache, a physical read is then performed to read the page into the buffer cache.
Is the physical read equal to the logical read?
In case no data in data cache, the physical read will be equal to number of logical read. Not necessarily, because a query could request the same page more than once. If the page doesn’t start in cache, the first will be a physical read, the others will not.