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) 1996-2008, PostgreSQL Global Development Group
   9  * Portions Copyright (c) 1994, Regents of the University of California
  10  *
  11  * $PostgreSQL$
  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: before 7.1, we also had to store references to the separate table
  31  * and index of a specific large object.  Now they all live in pg_largeobject
  32  * and are accessed via a common relation descriptor.
  33  *----------
  34  */
  35 typedef struct LargeObjectDesc
  36 {
  37         Oid                     id;                             /* LO's identifier */
  38         Snapshot        snapshot;               /* snapshot to use */
  39         SubTransactionId subid;         /* owning subtransaction ID */
  40         uint32          offset;                 /* current seek pointer */
  41         int                     flags;                  /* locking info, etc */
  42
  43 /* flag bits: */
  44 #define IFS_RDLOCK              (1 << 0)
  45 #define IFS_WRLOCK              (1 << 1)
  46
  47 } LargeObjectDesc;
  48
  49
  50 /*
  51  * Each "page" (tuple) of a large object can hold this much data
  52  *
  53  * We could set this as high as BLCKSZ less some overhead, but it seems
  54  * better to make it a smaller value, so that not as much space is used
  55  * up when a page-tuple is updated.  Note that the value is deliberately
  56  * chosen large enough to trigger the tuple toaster, so that we will
  57  * attempt to compress page tuples in-line.  (But they won't be moved off
  58  * unless the user creates a toast-table for pg_largeobject...)
  59  *
  60  * Also, it seems to be a smart move to make the page size be a power of 2,
  61  * since clients will often be written to send data in power-of-2 blocks.
  62  * This avoids unnecessary tuple updates caused by partial-page writes.
  63  */
  64 #define LOBLKSIZE               (BLCKSZ / 4)
  65
  66
  67 /*
  68  * Function definitions...
  69  */
  70
  71 /* inversion stuff in inv_api.c */
  72 extern void close_lo_relation(bool isCommit);
  73 extern Oid      inv_create(Oid lobjId);
  74 extern LargeObjectDesc *inv_open(Oid lobjId, int flags, MemoryContext mcxt);
  75 extern void inv_close(LargeObjectDesc *obj_desc);
  76 extern int      inv_drop(Oid lobjId);
  77 extern int      inv_seek(LargeObjectDesc *obj_desc, int offset, int whence);
  78 extern int      inv_tell(LargeObjectDesc *obj_desc);
  79 extern int      inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes);
  80 extern int      inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes);
  81 extern void inv_truncate(LargeObjectDesc *obj_desc, int len);
  82
  83 #endif   /* LARGE_OBJECT_H */