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What is hot block in Oracle?

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Mia Moss

Published Feb 20, 2026

What is hot block in Oracle?

A hot block is one that is accessed disproportionately often. One example would be an index block where the index is generated via a sequence; the database will need to write to the same block with the next value over and over again. This can make parallel operations difficult.

Also question is, what are hot blocks?

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Secondly, what is a block in Oracle? Oracle data blocks are the smallest units of storage that Oracle can use or allocate. In contrast, all data at the physical, operating system level is stored in bytes. Each operating system has what is called a block size. Oracle requests data in multiples of Oracle blocks, not operating system blocks.

Similarly, what is Oracle dirty block?

How does a block become dirty and what does Oracle to to clean-up a dirty block? Answer: In an nutshell, a dirty block is a block that has not yet been made "permanent", by writing the block to disk. Whenever a server process changes or modifies a data block, it becomes a dirty block.

How do you fix latch cache buffer chains?

Solving the cache buffers chain latch

Where there are hot blocks, you can relieve contention by doing one of the following: Splitting the buffer pool into multiple pools. Altering PCTFREE/PCTUSED to allow fewer rows per block, thus reducing contention on a certain block.

What is a dirty buffer?

A dirty buffer is a buffer whose contents have been modified. Dirty buffers are freed for reuse when DBWR has written the blocks to disk. The write list holds dirty buffers, which contain data that has been modified but has not yet been written to disk.

What is buffer gets in Oracle?

When Oracle requires a block it does a buffer get. First it checks to see if it already has the block it needs in memory. If so, the in-memory version is used. If it does not have the block in memory then it will read it from disk into memory. So a buffer get represents the number of times Oracle had to access a block.

What is Oracle Smon?

SMON (System MONitor) is an Oracle background process created when you start a database instance. The SMON process performs instance recovery, cleans up after dirty shutdowns and coalesces adjacent free extents into larger free extents. SMON must always be running for an instance.

What is Oracle PGA?

A Program Global Area (PGA) is a memory region that contains data and control information for a server process. It is nonshared memory created by Oracle Database when a server process is started. The PGA is used to process SQL statements and to hold logon and other session information.

What is Db_cache_size?

The db_cache_size initialization parameter (formerly db_block_buffers) governs the size of the RAM data buffer cache region. Staring in Oracle9i we also have separate database cache size parameters for multiple blocksizes, including db_nk_cache_size.

What is cache hit ratio in Oracle?

Oracle Metric Buffer Cache Hit Ratio Tips. The buffer hit ratio (BHR) indicates the current ratio of buffer cache hits to total requests, essentially the probability that a data block will be in-memory on a subsequent block re-read. A correctly tuned buffer cache can significantly improve overall database performance.

What is Pmon process in Oracle?

PMON (Process MONitor) is an Oracle background process created when you start a database instance. The PMON process will free up resources if a user process fails (eg. release database locks). PMON normally wakes up every 3 seconds to perform its housekeeping activities. PMON must always be running for an instance.

What is large pool in Oracle?

The large pool is an optional memory area. It provides an area of memory from which large allocations can be made. Oracle's backup and restore utilities typically allocate buffers that are hundreds of kilobytes in size. These will be allocated in the large pool if one is present.

What happens when checkpoint occurs in Oracle?

When a checkpoint occurs, Oracle ensures all modified buffers are written from the data buffer to disk files. Checkpoint checks every three seconds to see whether the amount of memory exceeds the value of the PGA_AGGREGATE_LIMIT parameter,and if so,takes action.

What are the three PL SQL block types?

PL/SQL is a block-structured language whose code is organized into blocks. A PL/SQL block consists of three sections: declaration, executable, and exception-handling sections. In a block, the executable section is mandatory while the declaration and exception-handling sections are optional. A PL/SQL block has a name.

What is block in SQL?

A block is a unit of code that provides execution and scoping boundaries for variable declarations and exception handling. PL/SQL allows you to create anonymous blocks (blocks of code that have no name) and named blocks, which may be packages, procedures, functions, triggers, or object types.

What data is in a block?

In computing (specifically data transmission and data storage), a block, sometimes called a physical record, is a sequence of bytes or bits, usually containing some whole number of records, having a maximum length; a block size. Data thus structured are said to be blocked.

How big is an Oracle block?

The default block size is 8k in Oracle. This is the most common. Sometimes, people create the database with 16k block size for datawarehouses. You can also find some 32k block size, but less common which means more bugs.

What is Dba_extents?

DBA_EXTENTS describes the extents comprising the segments in all tablespaces in the database. USER_EXTENTS describes the extents comprising the segments owned by the current user's objects. This view does not display the OWNER , FILE_ID , BLOCK_ID , or RELATIVE_FNO columns.

What is a tablespace Oracle?

An Oracle database consists of one or more logical storage units called tablespaces, which collectively store all of the database's data. Each tablespace in an Oracle database consists of one or more files called datafiles, which are physical structures that conform to the operating system in which Oracle is running.

What is trigger in SQL?

A trigger is a special type of stored procedure that automatically runs when an event occurs in the database server. DML triggers run when a user tries to modify data through a data manipulation language (DML) event. DML events are INSERT, UPDATE, or DELETE statements on a table or view.

What are the components of PL SQL block?

A PL/SQL block consists of up to three sections: declarative (optional), executable (required), and exception handling (optional).

Arvind209. Answered On : Jun 29th, 2008.
Component of PL/SQL Block are Begin(Optional), Declare(Mandatory), Exception(Optional), END(Mandatory).

What are the advantages of using PL SQL?

PL/SQL has these advantages:

Tight Integration with SQL.
High Performance.
High Productivity.
Portability.
Scalability.
Manageability.
Support for Object-Oriented Programming.
Support for Developing Web Applications.

What is cache buffer chain?

Description. The cache buffers chains latches are used to protect a buffer list in the buffer cache. These latches are used when searching for, adding, or removing a buffer from the buffer cache. Blocks in the buffer cache are placed on linked lists (cache buffer chains) which hang off a hash table.

What is latch free wait event Oracle?

The Oracle latch free wait event occurs when a session needs a latch, tries to get the latch, but fails because someone else has it. So, it sleeps with a wait on latch free, wakes up and tries again.

What is GC buffer busy acquire?

"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.

How do you resolve latch row cache objects?

The row cache object latch can also indicate SQL with excessive hard parsing or excessive reliance on data dictionary information such as views row-level security, synonyms, etc. The general solution for row cache latch waits is to increase shared_pool_size.

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