This article focuses on the new features aimed at database management. Self-management, or easy management, has been the key word for Oracle 10g. The main areas of enhancements are:
- Self-Managing Database
- Simplified Configuration of Shared Servers
- Transaction Manageability
- Simplified Statistics Collection
- Extended Support for FGA (Fine Grain Audit)
- Response File Creation during database install
One of the most important responsibilities of an Oracle Database Administrator or Performance Analyst, when it comes to performance diagnostics, is to determine how users access the database. This article is an attempt to show the different ways one can activate tracing of an Oracle session for performance diagnostics. While the Oracle documentation mentions some of the methods, it doesn't cover them all. This article consolidates many methods of tracing an Oracle session, some of which are well documented, as well as methods that are undocumented and reserved.
Is there any limit to the speed of Oracle? With Oracle announcing a new record one million transactions per minute, many believe that there is nothing that Oracle cannot do.
However, what if we have a requirement for a system that must accept high-volume data loads into a single table:
- 500,000 rows per second
- 50 megabytes per second
Is this possible? Using the right tricks you can make Oracle load data at unbelievable speed. However, special knowledge and tricks are required.
Oracle Managed Files (OMF), a new feature introduced in Oracle9i, enables the Oracle Server to automatically create and delete database files using standard operating system interfaces. This
feature hugely simplifies the job of the DBA, as the DBA doesn't need to interact with the underlying operating system to create and delete files.
When an Oracle Instance is started, the characteristics of the Instance are established by parameters specified within the initialization parameter file. These initialization parameters are either stored in a PFILE or SPFILE. SPFILEs are available in Oracle 9i and above. All prior releases of Oracle are using PFILEs.
Tables can be reorganized and redefined (evolved) on-line with the DBMS_REDEFINITION package. The process is similar to on-line rebuilds of indexes, in that the original table is left on-line, while a new copy of the table is built. However, an index index-rebuild is a singular operation, while table redefinition is a multi-step process.
When Oracle allocates space to a segment (like a table or index), a group of contiguous free blocks, called an extent, is added to the segment. Metadata regarding extent allocation and unallocated extents are either stored in the data dictionary, or in the tablespace itself. Tablespaces that record extent allocation in the dictionary, are called dictionary managed tablespaces, and tablespaces that record extent allocation in the tablespace header, are called locally managed tablespaces.
What are Temporary Tablespaces:
Temporary tablespaces are used to manage space for database sort operations and for storing global temporary tables. For example, if you join two large tables, and Oracle cannot do the sort in memory (see SORT_AREA_SIZE initialisation parameter), space will be allocated in a temporary tablespace for doing the sort operation. Other SQL operations that might require disk sorting are: CREATE INDEX, ANALYZE, Select DISTINCT, ORDER BY, GROUP BY, UNION, INTERSECT, MINUS, Sort-Merge joins, etc.
The DBA should assign a temporary tablespace to each user in the database to prevent them from allocating sort space in the SYSTEM tablespace. This can be done with one of the following commands:
In Oracle 8i and below, Rollback Segments provide read consistency and the ability to rollback transactions. In Oracle 9i, Undo segments can be used to provide this functionality. The advantage of using Automatic Undo Management is that it relieves the DBA of manually creating, sizing and monitoring the rollback segments in the database.
Both "db file sequential read" and "db file scattered read" events signify time waited for I/O read requests to complete. Time is reported in 100's of a second for Oracle 8i releases and below, and 1000's of a second for Oracle 9i and above. Most people confuse these events with each other as they think of how data is read from disk. Instead they should think of how data is read into the SGA buffer cache or user PGA memory.
db file sequential read:
A sequential read operation reads data into contiguous memory (usually a single-block read with p3=1, but can be multiple blocks). Single block I/Os are usually the result of using indexes. This event is also used for rebuilding the controlfile and reading datafile headers (P2=1). In general, this event is indicative of disk contention on index reads.