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/*-------------------------------------------------------------------------
*
* large_object.h
* Declarations for PostgreSQL large objects. POSTGRES 4.2 supported
* zillions of large objects (internal, external, jaquith, inversion).
* Now we only support inversion.
*
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/storage/large_object.h,v 1.40 2008/03/26 16:20:48 alvherre Exp $
*
*-------------------------------------------------------------------------
*/
#ifndef LARGE_OBJECT_H
#define LARGE_OBJECT_H
#include "utils/snapshot.h"
/*----------
* Data about a currently-open large object.
*
* id is the logical OID of the large object
* snapshot is the snapshot to use for read/write operations
* subid is the subtransaction that opened the desc (or currently owns it)
* offset is the current seek offset within the LO
* flags contains some flag bits
*
* NOTE: before 7.1, we also had to store references to the separate table
* and index of a specific large object. Now they all live in pg_largeobject
* and are accessed via a common relation descriptor.
*----------
*/
typedef struct LargeObjectDesc
{
Oid id; /* LO's identifier */
Snapshot snapshot; /* snapshot to use */
SubTransactionId subid; /* owning subtransaction ID */
uint32 offset; /* current seek pointer */
int flags; /* locking info, etc */
/* flag bits: */
#define IFS_RDLOCK (1 << 0)
#define IFS_WRLOCK (1 << 1)
} LargeObjectDesc;
/*
* Each "page" (tuple) of a large object can hold this much data
*
* We could set this as high as BLCKSZ less some overhead, but it seems
* better to make it a smaller value, so that not as much space is used
* up when a page-tuple is updated. Note that the value is deliberately
* chosen large enough to trigger the tuple toaster, so that we will
* attempt to compress page tuples in-line. (But they won't be moved off
* unless the user creates a toast-table for pg_largeobject...)
*
* Also, it seems to be a smart move to make the page size be a power of 2,
* since clients will often be written to send data in power-of-2 blocks.
* This avoids unnecessary tuple updates caused by partial-page writes.
*/
#define LOBLKSIZE (BLCKSZ / 4)
/*
* Function definitions...
*/
/* inversion stuff in inv_api.c */
extern void close_lo_relation(bool isCommit);
extern Oid inv_create(Oid lobjId);
extern LargeObjectDesc *inv_open(Oid lobjId, int flags, MemoryContext mcxt);
extern void inv_close(LargeObjectDesc *obj_desc);
extern int inv_drop(Oid lobjId);
extern int inv_seek(LargeObjectDesc *obj_desc, int offset, int whence);
extern int inv_tell(LargeObjectDesc *obj_desc);
extern int inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes);
extern int inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes);
extern void inv_truncate(LargeObjectDesc *obj_desc, int len);
#endif /* LARGE_OBJECT_H */
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