9.17.1 Hybrid Contiguous and linked file system

Advantages: 
 + rapid access to head of file
 + for small files (<N blocks) they are entirely contiguous
Disadvantages:
 - internal fragmentation (if N blocks is the smallest file size?)
 - external fragmentation (if we have different size of block arrays 
   on disk)

9.17.2 Extra FAT file pointers

O(1) access to end of file useful for append and truncate operations

doubly linked list would allow us to traverse forward or backward
through file. However this would not be of particular benefit 
compared to singly linked list in general.



9.17.3 Expected file size

expected file size == total available space / available num inodes



9.17.4 Ext4 extents




9.17.5 Access times

Expect RAM disk has lowest latency, but buffer cache may hide latency of
slower file systems

9.17.6 Database decisions

Monolithic file - single file handle, so can only access in one place
at once (multiple reader/writer threads would be blocked by OS file system)

Distinct files could permit multiple readers/writers, but require lots more open file handles

Monolithic file highly susceptible to file corruption - distinct files are more fault-tolerant.

Easy to mmap single monolithic file into memory for pointer-based access





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Corrections? email jeremy.singer@glasgow.ac.uk