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large_object.h
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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) 1996-2017, 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: in current usage, flag bit IFS_RDLOCK is *always* set, and we don't
31  * bother to test for it. Permission checks are made at first read or write
32  * attempt, not during inv_open(), so we have other bits to remember that.
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 #define IFS_RD_PERM_OK (1 << 2) /* read permission has been verified */
51 #define IFS_WR_PERM_OK (1 << 3) /* write permission has been verified */
52 
54 
55 
56 /*
57  * Each "page" (tuple) of a large object can hold this much data
58  *
59  * We could set this as high as BLCKSZ less some overhead, but it seems
60  * better to make it a smaller value, so that not as much space is used
61  * up when a page-tuple is updated. Note that the value is deliberately
62  * chosen large enough to trigger the tuple toaster, so that we will
63  * attempt to compress page tuples in-line. (But they won't be moved off
64  * unless the user creates a toast-table for pg_largeobject...)
65  *
66  * Also, it seems to be a smart move to make the page size be a power of 2,
67  * since clients will often be written to send data in power-of-2 blocks.
68  * This avoids unnecessary tuple updates caused by partial-page writes.
69  *
70  * NB: Changing LOBLKSIZE requires an initdb.
71  */
72 #define LOBLKSIZE (BLCKSZ / 4)
73 
74 /*
75  * Maximum length in bytes for a large object. To make this larger, we'd
76  * have to widen pg_largeobject.pageno as well as various internal variables.
77  */
78 #define MAX_LARGE_OBJECT_SIZE ((int64) INT_MAX * LOBLKSIZE)
79 
80 
81 /*
82  * Function definitions...
83  */
84 
85 /* inversion stuff in inv_api.c */
86 extern void close_lo_relation(bool isCommit);
87 extern Oid inv_create(Oid lobjId);
88 extern LargeObjectDesc *inv_open(Oid lobjId, int flags, MemoryContext mcxt);
89 extern void inv_close(LargeObjectDesc *obj_desc);
90 extern int inv_drop(Oid lobjId);
91 extern int64 inv_seek(LargeObjectDesc *obj_desc, int64 offset, int whence);
92 extern int64 inv_tell(LargeObjectDesc *obj_desc);
93 extern int inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes);
94 extern int inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes);
95 extern void inv_truncate(LargeObjectDesc *obj_desc, int64 len);
96 
97 #endif /* LARGE_OBJECT_H */
int inv_drop(Oid lobjId)
Definition: inv_api.c:336
void close_lo_relation(bool isCommit)
Definition: inv_api.c:102
LargeObjectDesc * inv_open(Oid lobjId, int flags, MemoryContext mcxt)
Definition: inv_api.c:265
int inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes)
Definition: inv_api.c:464
Oid inv_create(Oid lobjId)
Definition: inv_api.c:224
uint32 SubTransactionId
Definition: c.h:401
unsigned int Oid
Definition: postgres_ext.h:31
void inv_close(LargeObjectDesc *obj_desc)
Definition: inv_api.c:320
SubTransactionId subid
Definition: large_object.h:43
struct LargeObjectDesc LargeObjectDesc
Snapshot snapshot
Definition: large_object.h:42
void inv_truncate(LargeObjectDesc *obj_desc, int64 len)
Definition: inv_api.c:744
static char * buf
Definition: pg_test_fsync.c:65
int64 inv_seek(LargeObjectDesc *obj_desc, int64 offset, int whence)
Definition: inv_api.c:412
int inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes)
Definition: inv_api.c:551
int64 inv_tell(LargeObjectDesc *obj_desc)
Definition: inv_api.c:456