src/include/storage/large_object.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * large_object.h
   4  *        Declarations for PostgreSQL large objects.  POSTGRES 4.2 supported
   5  *        zillions of large objects (internal, external, jaquith, inversion).
   6  *        Now we only support inversion.
   7  *
   8  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
   9  * Portions Copyright (c) 1994, Regents of the University of California
  10  *
  11  * src/include/storage/large_object.h
  12  *
  13  *-------------------------------------------------------------------------
  14  */
  15 #ifndef LARGE_OBJECT_H
  16 #define LARGE_OBJECT_H
  17
  18 #include "utils/snapshot.h"
  19
  20
  21 /*----------
  22  * Data about a currently-open large object.
  23  *
  24  * id is the logical OID of the large object
  25  * snapshot is the snapshot to use for read/write operations
  26  * subid is the subtransaction that opened the desc (or currently owns it)
  27  * offset is the current seek offset within the LO
  28  * flags contains some flag bits
  29  *
  30  * NOTE: as of v11, permission checks are made when the large object is
  31  * opened; therefore IFS_RDLOCK/IFS_WRLOCK indicate that read or write mode
  32  * has been requested *and* the corresponding permission has been checked.
  33  *
  34  * NOTE: before 7.1, we also had to store references to the separate table
  35  * and index of a specific large object.  Now they all live in pg_largeobject
  36  * and are accessed via a common relation descriptor.
  37  *----------
  38  */
  39 typedef struct LargeObjectDesc
  40 {
  41         Oid                     id;                             /* LO's identifier */
  42         Snapshot        snapshot;               /* snapshot to use */
  43         SubTransactionId subid;         /* owning subtransaction ID */
  44         uint64          offset;                 /* current seek pointer */
  45         int                     flags;                  /* see flag bits below */
  46
  47 /* bits in flags: */
  48 #define IFS_RDLOCK              (1 << 0)        /* LO was opened for reading */
  49 #define IFS_WRLOCK              (1 << 1)        /* LO was opened for writing */
  50
  51 } LargeObjectDesc;
  52
  53
  54 /*
  55  * Each "page" (tuple) of a large object can hold this much data
  56  *
  57  * We could set this as high as BLCKSZ less some overhead, but it seems
  58  * better to make it a smaller value, so that not as much space is used
  59  * up when a page-tuple is updated.  Note that the value is deliberately
  60  * chosen large enough to trigger the tuple toaster, so that we will
  61  * attempt to compress page tuples in-line.  (But they won't be moved off
  62  * unless the user creates a toast-table for pg_largeobject...)
  63  *
  64  * Also, it seems to be a smart move to make the page size be a power of 2,
  65  * since clients will often be written to send data in power-of-2 blocks.
  66  * This avoids unnecessary tuple updates caused by partial-page writes.
  67  *
  68  * NB: Changing LOBLKSIZE requires an initdb.
  69  */
  70 #define LOBLKSIZE               (BLCKSZ / 4)
  71
  72 /*
  73  * Maximum length in bytes for a large object.  To make this larger, we'd
  74  * have to widen pg_largeobject.pageno as well as various internal variables.
  75  */
  76 #define MAX_LARGE_OBJECT_SIZE   ((int64) INT_MAX * LOBLKSIZE)
  77
  78
  79 /*
  80  * GUC: backwards-compatibility flag to suppress LO permission checks
  81  */
  82 extern bool lo_compat_privileges;
  83
  84 /*
  85  * Function definitions...
  86  */
  87
  88 /* inversion stuff in inv_api.c */
  89 extern void close_lo_relation(bool isCommit);
  90 extern Oid      inv_create(Oid lobjId);
  91 extern LargeObjectDesc *inv_open(Oid lobjId, int flags, MemoryContext mcxt);
  92 extern void inv_close(LargeObjectDesc *obj_desc);
  93 extern int      inv_drop(Oid lobjId);
  94 extern int64 inv_seek(LargeObjectDesc *obj_desc, int64 offset, int whence);
  95 extern int64 inv_tell(LargeObjectDesc *obj_desc);
  96 extern int      inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes);
  97 extern int      inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes);
  98 extern void inv_truncate(LargeObjectDesc *obj_desc, int64 len);
  99
 100 #endif                                                  /* LARGE_OBJECT_H */