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Database Utilities, 12c Release 1 (12.1)

BUFFER

Example: Calculating Buffer SizeThis section shows an example of how to calculate buffer size. The following table is created … 56 (30+2+22+2). To perform array operations for 100 rows, a buffer size of 5600 should be specified.

Database Utilities, 12c Release 1 (12.1)

BUFFER

BUFFERDefault: operating system-dependent The integer specified for BUFFER is the size, in bytes, of the … buffer through which data rows are transferred. BUFFER determines the number of rows in the array … inserted by Import. The following formula gives an approximation of the buffer size that inserts a … buffer

Database Utilities, 12c Release 1 (12.1)

BUFFER

BUFFERdetermine the default value for this parameter. Specifies the size, in bytes, of the buffer used to … Export. Use the following formula to calculate the buffer size: buffer_size = rows_in_array … . Note: The BUFFER parameter applies only to conventional path Export. It has no effect on a direct … path Export. For direct path Exports,

Database Concepts, 12c Release 1 (12.1)

Memory Architecture

Redo Log Buffer, channel_id FROM sales WHERE prod_id > 14 AND prod_id When using the buffer cache, the database … the buffer cache, and then discard the unwanted column values. Scanning data in row format in the … buffer cache requires many CPU instructions, and can result in poor CPU efficiency. When using the IM … Reference for a description

Database Concepts, 12c Release 1 (12.1)

Memory Architecture

Database Buffer CacheThe database buffer cache, also called the buffer cache, is the memory area that stores copies of … data blocks read from data files. A buffer is a main memory address in which the buffer manager … temporarily caches a currently or recently used data block. All users concurrently connected to a database instance share

Database Concepts, 12c Release 1 (12.1)

Glossary

bufferA main memory address in the database buffer cache. A buffer caches currently and recently used

Database Reference, 12c Release 1 (12.1)

buffer deadlock

C.3.17 buffer deadlockdeadlock by the cache layer. The cache layer cannot get a buffer in a certain mode within a certain

Database Reference, 12c Release 1 (12.1)

buffer latch

C.3.18 buffer latchThe session waits on the buffer hash chain latch. Primarily used in the dump routines. Wait Time: 1 … where addr = latch addr and a.latch# = b.latch#; chain# The index into array of buffer hash chains

Database Performance Tuning Guide, 12c Release 1 (12.1)

Tuning the Database Buffer Cache

Interpreting the Buffer Cache Hit RatioBefore deciding whether to increase or decrease the buffer cache size, you should first examine the … buffer cache hit ratio. A low cache hit ratio does not necessarily imply that increasing the size … of the buffer cache will benefit performance. Moreover, a high cache hit ratio may wrongly indicate … that the buffer

Database Performance Tuning Guide, 12c Release 1 (12.1)

Tuning the Database Buffer Cache

Using Multiple Buffer Poolssegment (compared to the size of the buffer cache) is accessed with a large or unbounded index range … percentage of the buffer cache, but it does not benefit from the cache. Very frequently accessed … that they do not age out of the buffer cache. However, the problem affects warm segments that are not … accessed frequently enough

Database Performance Tuning Guide, 12c Release 1 (12.1)

Tuning the Database Buffer Cache

Calculating the Buffer Pool Hit Ratio for Individual Buffer PoolsThe data in the V$SYSSTAT view reflects the logical and physical reads for all buffer pools within … one set of statistics. To determine the hit ratio for the buffer pools individually, query the V … for each pool. For more information about calculating hit ratios, see \" Calculating the Buffer Cache

Database Performance Tuning Guide, 12c Release 1 (12.1)

Tuning the Database Buffer Cache

Configuring the RECYCLE PoolYou can configure a RECYCLE buffer pool for blocks belonging to those segments that you do not want … object, then it is unlikely for a block stored in the buffer pool to be reused before it is aged out … . This is true regardless of the size of the buffer pool (given the constraint of the amount of available … be allocated to

Database Performance Tuning Guide, 12c Release 1 (12.1)

Tuning the Database Buffer Cache

Force Full Database Caching ModeAs more memory is added to a database, buffer cache sizes may continually grow. In some cases, the … size of the buffer cache may become so large that the entire database can fit into memory. The … the entire database in memory when the size of the database is smaller than the database buffer cache … buffer cache

Database Performance Tuning Guide, 12c Release 1 (12.1)

Tuning the Database Buffer Cache

Determining When to Use Force Full Database Caching Modewhenever the size of the database buffer cache is greater than the size of the database. Consider using … used space) is smaller than the individual buffer cache of each database instance in an Oracle RAC … smaller than 80% of the combined buffer cache sizes of all the database instances for well-partitioned

Database Performance Tuning Guide, 12c Release 1 (12.1)

Tuning the Database Buffer Cache

Increasing Memory Allocated to the Database Buffer Cache, consider increasing the size of the buffer cache. If possible, resize the buffer pools dynamically … buffer cache: Set the value of the DB_CACHE_ADVICE initialization parameter to ON. Allow the buffer … required to the buffer cache without causing the system to page, then allocate this memory. To increase

Database Performance Tuning Guide, 12c Release 1 (12.1)

Tuning the Database Buffer Cache

Configuring Multiple Buffer PoolsFor most systems, a single default buffer pool is generally adequate. However, database … administrators with detailed knowledge of an application's buffer pool may benefit from configuring multiple … buffer pools. For segments that have atypical access patterns, consider storing blocks from these … segments in two separate buffer

Database Performance Tuning Guide, 12c Release 1 (12.1)

Tuning the Database Buffer Cache

Configuring the Redo Log BufferServer processes making changes to data blocks in the buffer cache generate redo data into the log … buffer. The log writer process (LGWR) begins writing to copy entries from the redo log buffer to the … online redo log if any of the following conditions are true: The redo log buffer becomes at least … process

Database Performance Tuning Guide, 12c Release 1 (12.1)

Tuning the Database Buffer Cache

13 Tuning the Database Buffer CacheThis chapter describes how to tune the database buffer cache. If you are using automatic memory … Buffer Cache Configuring the Database Buffer Cache Configuring Multiple Buffer Pools Configuring the Redo Log Buffer Configuring the Database Caching Mode

Database Performance Tuning Guide, 12c Release 1 (12.1)

Tuning the Database Buffer Cache

Default Database Caching Modequeries a large table, because doing so might remove more useful data from the buffer cache. If the … Oracle Database instance determines that there is enough space to cache the full database in the buffer … database in the buffer cache. If the Oracle Database instance determines that there is not enough space … to cache the full

Database Performance Tuning Guide, 12c Release 1 (12.1)

Tuning the Database Buffer Cache

Verifying the Database Caching ModeBy default, Oracle Database runs in the default database caching mode. To verify if force full database caching mode is enabled: Query the V$DATABASE view as shown: SELECT FORCE_FULL_DB_CACHING FROM V$DATABASE; If the query returns a value of YES, then force full database caching mode is enabled on the database. If the query returns a value of NO, then force full database caching mode is disabled