【Datafile】Oracle單個datafile大小的限制

最近在維護資料庫空間，給tablespace新增datafile的時候，由於達到了資料庫最大datafile的個數，所以不能再新增。而我們的單個datafile的大小為2G，所以我就在想，單個datafile的大小限制到底是多少，我們可以相應擴大單個datafile的大小，以減少datafile的個數。

在網上參考了很多專業人士的技術文件，也做了相應的測試，現在記錄如下：

1、建立普通tablespace時，報錯

SYS@MTH> create tablespace TEST
2 datafile '/oradat/MTH/TEST01.dbf' size 2000M
3 autoextend on next 10M maxsize 50000M
4 extent management local
5 segment space management auto;
create tablespace TEST
*
ERROR at line 1:
ORA-03206: maximum file size of (6400000) blocks in AUTOEXTEND clause is out of range

2、Oracle官方相關限制設定

Item	Type of Limit	Limit Value
Database Block Size	Minimum	2048 bytes; must be a multiple of operating system physical block size
Database Block Size	Maximum	Operating system dependent; never more than 32 KB
Database Blocks	Minimum in initial extent of a segment	2 blocks
Database Blocks	Maximum per datafile	Platform dependent; typically 2^22 - 1 blocks
Controlfiles	Number of control files	1 minimum; 2 or more (on separate devices) strongly recommended
Controlfiles	Size of a control file	Dependent on operating system and database creation options; maximum of 25,000 x (database block size)
Database files	Maximum per tablespace	Operating system dependent; usually 1022
Database files	Maximum per database	65533 May be less on some operating systems Limited also by size of database blocks and by the DB_FILES initialization parameter for a particular instance
Database extents	Maximum per dictionary managed tablespace	4 GB * physical block size (with K/M modifier); 4 GB (without K/M modifier)
Database extents	Maximum per locally managed (uniform) tablespace	2 GB * physical block size (with K/M modifier); 2 GB (without K/M modifier)
Database file size	Maximum	Operating system dependent. Limited by maximum operating system file size; typically 2^22 or 4 MB blocks
MAXEXTENTS	Default value	Derived from tablespace default storage or DB_BLOCK_SIZE initialization parameter
MAXEXTENTS	Maximum	Unlimited
Redo Log Files	Maximum number of logfiles	Limited by value of MAXLOGFILES parameter in the CREATE DATABASE statement Control file can be resized to allow more entries; ultimately an operating system limit
Redo Log Files	Maximum number of logfiles per group	Unlimited
Redo Log File Size	Minimum size	4 MB
Redo Log File Size	Maximum Size	Operating system limit; typically 2 GB
Tablespaces	Maximum number per database	64 K Number of tablespaces cannot exceed the number of database files because each tablespace must include at least one file
Bigfile Tablespaces	Number of blocks	A bigfile tablespace contains only one datafile or tempfile, which can contain up to approximately 4 billion ( 2^32 ) blocks. The maximum size of the single datafile or tempfile is 128 terabytes (TB) for a tablespace with 32 K blocks and 32 TB for a tablespace with 8 K blocks.
Smallfile (traditional) Tablespaces	Number of blocks	A smallfile tablespace is a traditional Oracle tablespace, which can contain 1022 datafiles or tempfiles, each of which can contain up to approximately 4 million (2^22) blocks.
External Tables file	Maximum size	Dependent on the operating system. An external table can be composed of multiple files.

每個datafile最多包含2^22-1個block,存在這個限制是因為Oracle的內部ROWID使用22位2進位制數來儲存不同的block號，所以22位最多代表(2^22-1)個block。

3、根據文件，計算我的資料庫單個檔案的大小限制

SYS@MTH> show parameter db_block_size

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_block_size integer 8192

單個檔案的最大大小：(2^22-1) × 8K=33554432K=32G

顯然我指定的50000M超過了最大限制，所以報錯。

檢視到文件中建議單個datafile的大小設定成8G，既避免datafile過小導致的個數過多，難以維護，又能避免datafile過大，一旦出現問題很難恢復的情況。

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/30776559/viewspace-2146790/，如需轉載，請註明出處，否則將追究法律責任。

【Datafile】Oracle單個datafile大小的限制

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