File Manager (cont)
The "magnetic disk storage manager" (storage/smgr/md.c )
- manages its own pool of open file descriptors (Vfd's)
- may use several Vfd's to access data, if several forks
- manages mapping from
PageID to file+offset.
PostgreSQL PageID values are structured:
typedef struct
{
RelFileNode rnode;
ForkNumber forkNum;
BlockNumber blockNum;
} BufferTag;
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