Articles tagged

Invisible Columns In Oracle Database 12C

0
3
In Oracle Database 12c, you can set a column in table as invisible either during CREATE TABLE or modifying existing table via ALTER TABLE command. By default, table columns are always visible. When you make it invisible, the COL# column in COL$ dictionary is updated to 0, and so is not included in the “SELECT *” or “INSERT INTO VALUES”… Read more

Oracle Database 12.1.0.2c: Hot Cloning Of Pluggable Databases

1
3
Cloning of a Pluggable Database (PDB) in Oracle Multitenant is a great feature and is very useful. Oracle Database 12c Release 1 has introduced various enhancements to the cloning of Pluggable Databases to overcome the limitations imposed by the initial release of Oracle Database 12c (12.1.0.1). In Oracle 12.1.0.2c: PDBs can be hot cloned, i.e. you don’t need to put the source PDB… Read more

Oracle Database 12.1.0.2c: Automatic Big Table Cache

0
0
Serial direct path reads were first introduced in Oracle 11g to prevent wiping out a large number of buffers from the buffer cache by a serial large table scan. As a result, big tables accessed via serial Full Table Scans bypass the Buffer Cache and read data from the Data Files into the users’ Program Global Area (PGA). This prevents flooding… Read more

ASM Proxy: New Instance Type in Oracle 12c

0
2
Prior to Oracle Database 12c, an ASM instance ran on every node in the cluster and ASM Cluster File System (ACFS) Service on a node connected to the local ASM instance running on the same host to fetch the required metadata. If the ASM instance on a node were to fail, then ACFS file systems could no longer be accessed… Read more

12c Histogram: TOP-Frequency

0
1
As of Oracle version 12.1, if a number of buckets N in a histogram is less than the number of distinct values in the data set, Oracle will not generate the instable and imprecise legacy Height Balanced histogram. Instead, two new types of histogram are possible: TOP-Frequency and Hybrid. In order to select between the later and the former ty… Read more

Basics of the Cost Based Optimizer – part 6

0
0
In part 5 of this series I started working through a list of queries designed to demonstrate ways in which the optimizer can produce bad cardinality estimates. In this installment I’m going work through the remainder of the list. The outstanding queries are as follows: select count(*) from t1 where trunc_5 > ( select max(trunc_5) from t1 where mod_200 =… Read more

TSPITR Using ACFS Snapshots

0
0
Starting with Oracle Grid Infrastructure 12c (12.1), Oracle Cloud File system (ASM Cluster File System in cluster environment) supports database files (database version 11.2.0.4 and up) in addition to general-purpose files so that entire Oracle databases can be stored inside Oracle Cloud FS. In my earlier articles I demonstrated that: For a database having its files stored on Oracle Cloud… Read more

Upgrading A Database Using Recovery Manager (RMAN) Duplicate Command In Oracle 12c

0
1
Introduction For versions of Oracle 11g R2, Oracle Recovery Manager (RMAN) replicates a database to a different Oracle home and opens it with NORESET LOGS option. From Oracle 12cR1, database RMAN introduced an option called ‘NO OPEN’, which duplicates your database to a new location and keeps it in an unopened state. Using this feature we can duplicate a databas… Read more

12c: Database Backups Using ACFS Snapshots

1
1
Starting with Oracle Grid Infrastructure 12c (12.1), Oracle Cloud File system (ASM Cluster File System in cluster environment ) supports database files (database version 11.2.0.4 and up) in addition to general purpose files so that entire Oracle databases can be stored inside Oracle Cloud FS and can leverage the Advanced Data Services such as snapshots, tagging and auditing although replication and… Read more