Table of Contents
What are Oracle context switches?
Whenever you use PL/SQL in SQL statements, the Oracle engine needs to switch from doing SQL to doing PL/SQL, and switch back after it is done. Generally, this is called a “context switch”.
What is context switching?
In computing, a context switch is the process of storing the state of a process or thread, so that it can be restored and resume execution at a later point. In a multitasking context, it refers to the process of storing the system state for one task, so that task can be paused and another task resumed.
What is context switching in Oracle Plsql?
It’s called a context switch. The PL/SQL engine passes the SQL statement, along with bind variable values, over to the SQL engine. The SQL engine does its thing and then passes the results back to the PL/SQL engine, which continues right along.
What is context switching in SQL?
Context switching refers to modifying the context in which code operates from one user to another. The same code can function differently across user contexts because database role memberships and permissions may differ between users. The Execute As statement in T-SQL can implement context switching.
Why bulk collect is faster in Oracle?
Since the BULK COLLECT fetches the record in BULK, the INTO clause should always contain a collection type variable. The main advantage of using BULK COLLECT is it increases the performance by reducing the interaction between database and PL/SQL engine.
What is Oracle context area?
Oracle creates a memory area, known as the context area, for processing an SQL statement, which contains all the information needed for processing the statement; for example, the number of rows processed, etc. A cursor is a pointer to this context area. PL/SQL controls the context area through a cursor.
Why do we need context switching?
The need for Context switching. A context switching helps to share a single CPU across all processes to complete its execution and store the system’s tasks status. When the process reloads in the system, the execution of the process starts at the same point where there is conflicting.
How do you write a context switch?
Context Switching Steps
- Save the context of the process that is currently running on the CPU.
- Move the process control block of the above process into the relevant queue such as the ready queue, I/O queue etc.
- Select a new process for execution.
- Update the process control block of the selected process.
What is high context switching?
A high context switch rate in the operating system (OS) signals that the OS is handling many different tasks and must alternate between them. In a DB2® system, this usually causes latch contention or the presence of many database connections. A slow down in SQL query performance can be the result.
What are ref CURSORs in Oracle?
A REF CURSOR is a PL/SQL data type whose value is the memory address of a query work area on the database. In essence, a REF CURSOR is a pointer or a handle to a result set on the database. REF CURSOR s are represented through the OracleRefCursor ODP.NET class.
Why collections are used in Oracle?
Developers utilize collections to ‘cache’ static data that needs to be regularly accessed. This results in reduced calls to a database. Oracle provides three types of PL/SQL collections: nested tables, varrays, and associative arrays. We will review each of these collection types in turn.
CONTEXT SWITCHING. When we consider “CONTEXT SWITCHING” in relation to Oracle Database, we specifically refer to the exchange of processing control between the SQL and PL/SQL engines (without necessarily understanding what occurs in such a process).
What is context switch in PL SQL?
SQL statements are called from PL/SQL in a loop, so the execution will switch back and forth between the PL/SQL engine and the SQL engine. This switch between two environments is known as a context switch. Context switches increase elapsed time of your programs and introduce unnecessary CPU overhead.
How do I switch from SQL to PL SQL?
Remember that the context switch works both ways: SQL -> PL/SQL and PL/SQL -> SQL. You can reduce the overhead of going from SQL to PL/SQL by declaring your function with the UDF pragma (12c+) or defining it with the WITH FUNCTION clause (also 12c+).