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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) 1996-2021, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/large_object.h
*
*-------------------------------------------------------------------------
*/
#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: as of v11, permission checks are made when the large object is
* opened; therefore IFS_RDLOCK/IFS_WRLOCK indicate that read or write mode
* has been requested *and* the corresponding permission has been checked.
*
* 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 */
uint64 offset; /* current seek pointer */
int flags; /* see flag bits below */
/* bits in flags: */
#define IFS_RDLOCK (1 << 0) /* LO was opened for reading */
#define IFS_WRLOCK (1 << 1) /* LO was opened for writing */
} 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.
*
* NB: Changing LOBLKSIZE requires an initdb.
*/
#define LOBLKSIZE (BLCKSZ / 4)
/*
* Maximum length in bytes for a large object. To make this larger, we'd
* have to widen pg_largeobject.pageno as well as various internal variables.
*/
#define MAX_LARGE_OBJECT_SIZE ((int64) INT_MAX * LOBLKSIZE)
/*
* GUC: backwards-compatibility flag to suppress LO permission checks
*/
extern bool lo_compat_privileges;
/*
* 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 int64 inv_seek(LargeObjectDesc *obj_desc, int64 offset, int whence);
extern int64 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, int64 len);
#endif /* LARGE_OBJECT_H */
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