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8ec569479f
Up until now, we've had a policy of only marking certain variables in the PostgreSQL header files with PGDLLIMPORT, but now we've decided to mark them all. This means that extensions running on Windows should no longer operate at a disadvantage as compared to extensions running on Linux: if the variable is present in a header file, it should be accessible. Discussion: http://postgr.es/m/CA+TgmoYanc1_FSfimhgiWSqVyP5KKmh5NP2BWNwDhO8Pg2vGYQ@mail.gmail.com
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) 1996-2022, 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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