Physical and Logical Database Limits in Oracle

Logical Database Limits in Oracle

1)CREATE MATERIALIZED VIEW definition size Limit
Maximum size: 64K Bytes

2)GROUP BY clause size Limit
Maximum length: Must fit within a single database block.

3)Indexes Limit
Maximum per table: Unlimited
Total size of indexed column: 75% of the database block size minus some overhead

4)Columns Limit
Maximum Per table: 1000
Maximum Per index (or clustered index): 32
Maximum Per bitmapped index: 30

5)Constraints
Maximum per column: Unlimited

6)Subqueries
Maximum levels of subqueries in a SQL statement in the FORM clause of top-level query: Unlimited
Maximum levels of subqueries in a SQL statement in the WHERE clause: 255

7)Partitions
Maximum length of linear partitioning key: 4 KB - overhead
Maximum number of columns in partition key: 16 columns
Maximum number of partitions allowed per table or index: 1024K - 1

8)Rows
Maximum number per table: Unlimited

9)Stored Packages
Maximum size: Limits typically range from 2000 to 3000 lines of code.

10)Trigger Cascade Limit
Maximum value: Operating system-dependent, typically 32

11)Users and Roles
Maximum: 2,147,483,638

12)Tables
Maximum per clustered table: 32 tables
Maximum per database: Unlimited

Physical Database Limits in oracle 

1)Data Block Size Limit
Minimum: 2048 bytes; must be a multiple of operating system physical block size
Maximum: Operating system dependent; Not more than 32 KB

2)Data Blocks Limit
Minimum in initial extent of a segment: 2 data blocks
Maximum per datafile: Platform dependent; typically power(2,22) - 1 blocks

3)Controlfiles Limit
Number of control files: 1 minimum; 2 or more (on separate devices) strongly recommended.
Size of a control file: Maximum of 20,000 * (database block size)

4)Datafiles Limit
Maximum per tablespace: 1022
Maximum per database: 65533

Also, limited by the DB_FILES initialization parameter for a particular instance.

5)Database extents Limit
Maximum per dictionary managed tablespace: 4 GB * physical block size.
Maximum per locally managed (uniform) tablespace: 2 GB * physical block size.

6)Database file size Limit
Limited by maximum operating system file size.

7)MAXEXTENTS Limit
Default value: Derived from tablespace default storage or DB_BLOCK_SIZE initialization parameter
Maximum: Unlimited

8)Redo Log Files Limit
Maximum number of logfiles: Limited by value of MAXLOGFILES parameter in the CREATE DATABASE statement.
Maximum number of logfiles per group: Unlimited

9)Redo Log File Size Limit
Minimum size: 50 KB
Maximum size: Operating system limit.

10)Tablespaces:
Maximum number per database: 65533

11)Bigfile Tablespaces
Number of blocks: power(2,32)

12)Smallfile Tablespaces:
Number of blocks: power(2,22)

13)External Tables file
Maximum size: OS dependent.

Process and Runtime Limits

1)Instances per database
Maximum number of cluster database instances per database: Operating system-dependent

2)Locks
Row-level: Unlimited
Distributed Lock Manager: Operating system dependent

3)SGA size
Maximum value: Operating system-dependent;
For 32 bit OS, 2GB - 4GB.
For 64 bit OS, >4GB.

4)Advanced Queuing Processes
Maximum per instance: 10

5)Job Queue Processes
Maximum per instance: 1000

6)I/O Slave Processes
Maximum per background process (DBWR, LGWR, ....): 15
Maximum per Backup session: 15

7)Sessions
Maximum per instance: 32 KB; Restricted by the PROCESSES and SESSIONS initialization parameters.

8)Global Cache Service Processes
Maximum per instance: 10

9)Shared Servers
Maximum per instance: Unlimited. Restricted by the PROCESSES and SESSIONS initialization parameters.

10)Dispatchers
Maximum per instance: Unlimited. Restricted by the PROCESSES and SESSIONS initialization parameters.

11)Parallel Execution Slaves
Maximum per instance: Unlimited. Restricted by the PROCESSES and SESSIONS initialization parameters.

12)Backup Sessions
Maximum per instance: Unlimited. Restricted by the PROCESSES and SESSIONS initialization parameters.

ORA-01450: maximum key length (3215) exceeded

Error Description
Whenever I try to rebuild index online then it fails with message ORA-00604: error occurred at recursive SQL level 1 along with ORA-01450: maximum key length (3215) exceeded. Below is the scenario.
SQL> create table tab1(a varchar2(3000),b varchar2(2000));
Table created.

SQL> create index tab1_I on tab1(a,b);
Index created.

SQL> alter index tab1_I rebuild online;
alter index tab1_I rebuild online
*
ERROR at line 1:
ORA-00604: error occurred at recursive SQL level 1
ORA-01450: maximum key length (3215) exceeded

Let's now create one table with column length 3000+199=3199 bytes and see what happens.
SQL> create table tab3(a varchar2(3000),b varchar2(199));
Table created.

SQL> create index tab3_I on tab3(a,b);
Index created.

Try to rebuild it online and it works.
SQL> alter index tab3_I rebuild online;
Index altered.

Now just add extra 1 bytes on column b. And whenever we try to rebuild it online it will fail.

SQL> alter table tab3 modify b varchar2(200);
Table altered.

SQL> alter index tab3_I rebuild online;
alter index tab3_I rebuild online
*
ERROR at line 1:
ORA-00604: error occurred at recursive SQL level 1
ORA-01450: maximum key length (3215) exceeded

Cause of the Problem
When creating a index the total length of the index cannot exceed a certain value. Primarily this value depends on DB_BLOCK_SIZE.
If 2K block size then maximum index key length=758
If 4K block size then maximum index key length=1578
If 8K block size then maximum index key length=3218
If 16K block size then maximum index key length=6498
How the maximum index key length is measured by?
Maximum index key length=Total index length (Sum of width of all indexed column+the number of indexed columns)+Length of the key(2 bytes)+ROWID(6 bytes)+the length of the rowid(1 byte)

The index key size is limited by the value of db_block_size, because a key value may not span multiple blocks. So, based on the size of the block size of index depends. In fact, it is required that any index block must contain at least TWO index entries per block.

So we can say that the maximum key length for an index will be less than half of
the DB_BLOCK_SIZE. But we know that in a block there also needed space for PCTFREE, INITRANS and space for block overhead(Block Header,ROW Directory, Table Directory, etc). After considering these bytes the actual space that can be used for the Index key is actually just over 1/3 of the DB_BLOCK_SIZE.

Solution of the Problem
The causes already indicates what might be the solutions. Solution may be,
1)Increase your database block size. Create a tablespace with bigger block size and create index on that tablespace.

2)If you have index on multiple columns then you can split index to single or 2 columns so that size does not extended over it can handle.

3)Rebuild the index without online clause. That is
ALTER INDEX index_name REBUILD;
Because The online rebuild of the index creates a journal table and index. This internal journal IOT table contains more columns in its index. This is a feature of online rebuild. This time the error arises because that current value of the initialization parameter db_block_size is not large enough to create internal journal IOT.