stasis-aries-wal/src/lladd/blobManager.h

#ifndef __BLOB_MANAGER_H
#define __BLOB_MANAGER_H

#include <lladd/common.h>
BEGIN_C_DECLS

/**    
       @file
       blobManager - Provides blob handling.
 
       Plan for modularity: Exactly one blob manager per storeFile.
       Alternatively, we could use the bufferManager's record length
       field to allow for more than one blob manager per buffer
       manager.  (Right now, this field is set to a special value for
       blobs; thie could be extended for other types of records.)

       Blob manager interacts with page manger via page manager's
       public api.

       Blob updates work as follows:

       (1) A transaction obtains an exclusive write lock on a blob
           (not implemented yet.)

       (2) When it requests a write, the blob it writes to is added to
           a data structure that lists all dirty blobs by transaction,
           and the page containing the blob entry is updated. (The fd
           bit in the record is flipped, and the LSN is updated.)  The
           write to the blob store is not flushed to disk.
       
       (3) All subsequent writes to the same blob just update the
           backing file.

       (4) On commit and rollback, the data structure containing the xid's
           dirty blobs is destroyed.

       (5) recovery2.c handles the restoration of the fd bits using
           physical logging (this is automatic, since we use Tset()
           calls to update the records.)
       
       @todo Should the tripleHash be its own little support library? 
       @todo Set range??

       @ingroup LLADD_CORE
*/


/** 
    Read the blob from the recordid rid into buf.
*/
void readBlob(int xid, Page * p,  recordid rid, void * buf);


/** 
    Write the contents of buf to the blob in recordid rid.
*/
void writeBlob(int xid, Page * p, lsn_t lsn, recordid rid, const void * buf);

compensated_function recordid preAllocBlob(int xid, long blobsize);
compensated_function recordid preAllocBlobFromPage(int xid, long page, long blobsize);

/**
   Allocate a blob of size blobSize. 

   @todo This function does not atomically allocate space in the blob
   file.  Instead of trusting the blob store length, upon recieving a
   log entry, update a static file length variable in blobManager.

*/

void allocBlob(int xid, recordid rid);

END_C_DECLS

#endif