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/*------------------------------------------------------------------------- * * large_object.h * Declarations for PostgreSQL large objects. POSTGRES 4.2 supported * zillions of large objects (internal, external, jaquith, inversion). * Now we only support inversion. * * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * src/include/storage/large_object.h * *------------------------------------------------------------------------- */ #ifndef LARGE_OBJECT_H #define LARGE_OBJECT_H #include "utils/snapshot.h" /*---------- * Data about a currently-open large object. * * id is the logical OID of the large object * snapshot is the snapshot to use for read/write operations * subid is the subtransaction that opened the desc (or currently owns it) * offset is the current seek offset within the LO * flags contains some flag bits * * NOTE: before 7.1, we also had to store references to the separate table * and index of a specific large object. Now they all live in pg_largeobject * and are accessed via a common relation descriptor. *---------- */ typedef struct LargeObjectDesc { Oid id; /* LO's identifier */ Snapshot snapshot; /* snapshot to use */ SubTransactionId subid; /* owning subtransaction ID */ uint32 offset; /* current seek pointer */ int flags; /* locking info, etc */ /* flag bits: */ #define IFS_RDLOCK (1 << 0) #define IFS_WRLOCK (1 << 1) } LargeObjectDesc; /* * Each "page" (tuple) of a large object can hold this much data * * We could set this as high as BLCKSZ less some overhead, but it seems * better to make it a smaller value, so that not as much space is used * up when a page-tuple is updated. Note that the value is deliberately * chosen large enough to trigger the tuple toaster, so that we will * attempt to compress page tuples in-line. (But they won't be moved off * unless the user creates a toast-table for pg_largeobject...) * * Also, it seems to be a smart move to make the page size be a power of 2, * since clients will often be written to send data in power-of-2 blocks. * This avoids unnecessary tuple updates caused by partial-page writes. */ #define LOBLKSIZE (BLCKSZ / 4) /* * Function definitions... */ /* inversion stuff in inv_api.c */ extern void close_lo_relation(bool isCommit); extern Oid inv_create(Oid lobjId); extern LargeObjectDesc *inv_open(Oid lobjId, int flags, MemoryContext mcxt); extern void inv_close(LargeObjectDesc *obj_desc); extern int inv_drop(Oid lobjId); extern int inv_seek(LargeObjectDesc *obj_desc, int offset, int whence); extern int inv_tell(LargeObjectDesc *obj_desc); extern int inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes); extern int inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes); extern void inv_truncate(LargeObjectDesc *obj_desc, int len); #endif /* LARGE_OBJECT_H */