101 lines
3.6 KiB
C
101 lines
3.6 KiB
C
/*-------------------------------------------------------------------------
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*
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* large_object.h
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* Declarations for PostgreSQL large objects. POSTGRES 4.2 supported
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* zillions of large objects (internal, external, jaquith, inversion).
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* Now we only support inversion.
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*
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* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/storage/large_object.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef LARGE_OBJECT_H
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#define LARGE_OBJECT_H
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#include "utils/snapshot.h"
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/*----------
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* Data about a currently-open large object.
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*
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* id is the logical OID of the large object
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* snapshot is the snapshot to use for read/write operations
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* subid is the subtransaction that opened the desc (or currently owns it)
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* offset is the current seek offset within the LO
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* flags contains some flag bits
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*
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* NOTE: as of v11, permission checks are made when the large object is
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* opened; therefore IFS_RDLOCK/IFS_WRLOCK indicate that read or write mode
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* has been requested *and* the corresponding permission has been checked.
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*
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* NOTE: before 7.1, we also had to store references to the separate table
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* and index of a specific large object. Now they all live in pg_largeobject
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* and are accessed via a common relation descriptor.
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*----------
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*/
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typedef struct LargeObjectDesc
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{
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Oid id; /* LO's identifier */
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Snapshot snapshot; /* snapshot to use */
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SubTransactionId subid; /* owning subtransaction ID */
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uint64 offset; /* current seek pointer */
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int flags; /* see flag bits below */
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/* bits in flags: */
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#define IFS_RDLOCK (1 << 0) /* LO was opened for reading */
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#define IFS_WRLOCK (1 << 1) /* LO was opened for writing */
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} LargeObjectDesc;
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/*
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* Each "page" (tuple) of a large object can hold this much data
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*
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* We could set this as high as BLCKSZ less some overhead, but it seems
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* better to make it a smaller value, so that not as much space is used
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* up when a page-tuple is updated. Note that the value is deliberately
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* chosen large enough to trigger the tuple toaster, so that we will
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* attempt to compress page tuples in-line. (But they won't be moved off
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* unless the user creates a toast-table for pg_largeobject...)
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*
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* Also, it seems to be a smart move to make the page size be a power of 2,
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* since clients will often be written to send data in power-of-2 blocks.
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* This avoids unnecessary tuple updates caused by partial-page writes.
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*
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* NB: Changing LOBLKSIZE requires an initdb.
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*/
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#define LOBLKSIZE (BLCKSZ / 4)
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/*
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* Maximum length in bytes for a large object. To make this larger, we'd
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* have to widen pg_largeobject.pageno as well as various internal variables.
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*/
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#define MAX_LARGE_OBJECT_SIZE ((int64) INT_MAX * LOBLKSIZE)
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/*
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* GUC: backwards-compatibility flag to suppress LO permission checks
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*/
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extern PGDLLIMPORT bool lo_compat_privileges;
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/*
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* Function definitions...
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*/
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/* inversion stuff in inv_api.c */
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extern void close_lo_relation(bool isCommit);
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extern Oid inv_create(Oid lobjId);
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extern LargeObjectDesc *inv_open(Oid lobjId, int flags, MemoryContext mcxt);
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extern void inv_close(LargeObjectDesc *obj_desc);
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extern int inv_drop(Oid lobjId);
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extern int64 inv_seek(LargeObjectDesc *obj_desc, int64 offset, int whence);
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extern int64 inv_tell(LargeObjectDesc *obj_desc);
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extern int inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes);
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extern int inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes);
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extern void inv_truncate(LargeObjectDesc *obj_desc, int64 len);
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#endif /* LARGE_OBJECT_H */
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