FairCom ISAM for C

File Size and Operating System Limits

Different platforms support different maximum file sizes. The limit is imposed by the data type for the value used to seek to a given offset in a file. Older operating systems use a 4-byte signed offset, allowing physical files up to 2 GB. Newer platforms use 4-byte unsigned offsets (4 GB) or 8-byte unsigned offsets (16,000,000 terabytes = 18 exabytes).

On systems supporting only 4-byte signed offsets:

• Standard c-tree files can grow up to 2 GB in size.
• Extended files (also referred to as "huge" files) can be segmented into multiple physical files up to 2 GB each, allowing a single logical file to grow:
  • To 4 GB using only segmented file support (using segments <= 2 GB each)
  • Up to 16,000,000 terabytes using segmented file support and huge file support (using segments <= 2 GB each)

The following platforms are limited to 2 GB files:

AT&T SVR4	SunOS	HP-UX 10
IBM AIX 3.2-4.1	Linux (before kernel 2.400)	SCO OpenServer/UnixWare
Macintosh (7-9, OS X)	QNX 2 & 4

On systems supporting a 4-byte unsigned offset:

• Standard c-tree files can grow up to 4 GB in size.
• Extended files using huge file support and segmented file support can grow to 18 exabytes (using segments <= 4 GB each).

The following platforms fall into this category:

Windows 95 and 98 - FAT file system

Solaris 2.6 (Intel/SPARC)

On systems supporting 8-byte offsets:

• Extended format files with huge file support can grow up to 18 exabytes.
• Segmented file support is optional, but convenient for allocating portions of files to different volumes.
• Standard c-tree files can grow up to 4 GB in size.

The following platforms fall into this category:

Windows NT/2000 and above - NTFS file system	HP-UX 11
AIX 4.2 and above	Solaris 7 and above (Intel and SPARC)
Linux (kernel 2.400 or later)	FreeBSD

File Handles/Descriptors

FairCom DB must request a file handle (file descriptor) for each file it has open.

The number of concurrent file handles is limited to 32768.