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Diffstat (limited to 'src/backend/catalog/pg_largeobject.c')
| -rw-r--r-- | src/backend/catalog/pg_largeobject.c | 187 |
1 files changed, 187 insertions, 0 deletions
diff --git a/src/backend/catalog/pg_largeobject.c b/src/backend/catalog/pg_largeobject.c new file mode 100644 index 0000000..ae9365e --- /dev/null +++ b/src/backend/catalog/pg_largeobject.c @@ -0,0 +1,187 @@ +/*------------------------------------------------------------------------- + * + * pg_largeobject.c + * routines to support manipulation of the pg_largeobject relation + * + * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * + * IDENTIFICATION + * src/backend/catalog/pg_largeobject.c + * + *------------------------------------------------------------------------- + */ +#include "postgres.h" + +#include "access/genam.h" +#include "access/htup_details.h" +#include "access/sysattr.h" +#include "access/table.h" +#include "catalog/catalog.h" +#include "catalog/dependency.h" +#include "catalog/indexing.h" +#include "catalog/pg_largeobject.h" +#include "catalog/pg_largeobject_metadata.h" +#include "miscadmin.h" +#include "utils/acl.h" +#include "utils/fmgroids.h" +#include "utils/rel.h" + + +/* + * Create a large object having the given LO identifier. + * + * We create a new large object by inserting an entry into + * pg_largeobject_metadata without any data pages, so that the object + * will appear to exist with size 0. + */ +Oid +LargeObjectCreate(Oid loid) +{ + Relation pg_lo_meta; + HeapTuple ntup; + Oid loid_new; + Datum values[Natts_pg_largeobject_metadata]; + bool nulls[Natts_pg_largeobject_metadata]; + + pg_lo_meta = table_open(LargeObjectMetadataRelationId, + RowExclusiveLock); + + /* + * Insert metadata of the largeobject + */ + memset(values, 0, sizeof(values)); + memset(nulls, false, sizeof(nulls)); + + if (OidIsValid(loid)) + loid_new = loid; + else + loid_new = GetNewOidWithIndex(pg_lo_meta, + LargeObjectMetadataOidIndexId, + Anum_pg_largeobject_metadata_oid); + + values[Anum_pg_largeobject_metadata_oid - 1] = ObjectIdGetDatum(loid_new); + values[Anum_pg_largeobject_metadata_lomowner - 1] + = ObjectIdGetDatum(GetUserId()); + nulls[Anum_pg_largeobject_metadata_lomacl - 1] = true; + + ntup = heap_form_tuple(RelationGetDescr(pg_lo_meta), + values, nulls); + + CatalogTupleInsert(pg_lo_meta, ntup); + + heap_freetuple(ntup); + + table_close(pg_lo_meta, RowExclusiveLock); + + return loid_new; +} + +/* + * Drop a large object having the given LO identifier. Both the data pages + * and metadata must be dropped. + */ +void +LargeObjectDrop(Oid loid) +{ + Relation pg_lo_meta; + Relation pg_largeobject; + ScanKeyData skey[1]; + SysScanDesc scan; + HeapTuple tuple; + + pg_lo_meta = table_open(LargeObjectMetadataRelationId, + RowExclusiveLock); + + pg_largeobject = table_open(LargeObjectRelationId, + RowExclusiveLock); + + /* + * Delete an entry from pg_largeobject_metadata + */ + ScanKeyInit(&skey[0], + Anum_pg_largeobject_metadata_oid, + BTEqualStrategyNumber, F_OIDEQ, + ObjectIdGetDatum(loid)); + + scan = systable_beginscan(pg_lo_meta, + LargeObjectMetadataOidIndexId, true, + NULL, 1, skey); + + tuple = systable_getnext(scan); + if (!HeapTupleIsValid(tuple)) + ereport(ERROR, + (errcode(ERRCODE_UNDEFINED_OBJECT), + errmsg("large object %u does not exist", loid))); + + CatalogTupleDelete(pg_lo_meta, &tuple->t_self); + + systable_endscan(scan); + + /* + * Delete all the associated entries from pg_largeobject + */ + ScanKeyInit(&skey[0], + Anum_pg_largeobject_loid, + BTEqualStrategyNumber, F_OIDEQ, + ObjectIdGetDatum(loid)); + + scan = systable_beginscan(pg_largeobject, + LargeObjectLOidPNIndexId, true, + NULL, 1, skey); + while (HeapTupleIsValid(tuple = systable_getnext(scan))) + { + CatalogTupleDelete(pg_largeobject, &tuple->t_self); + } + + systable_endscan(scan); + + table_close(pg_largeobject, RowExclusiveLock); + + table_close(pg_lo_meta, RowExclusiveLock); +} + +/* + * LargeObjectExists + * + * We don't use the system cache for large object metadata, for fear of + * using too much local memory. + * + * This function always scans the system catalog using an up-to-date snapshot, + * so it should not be used when a large object is opened in read-only mode + * (because large objects opened in read only mode are supposed to be viewed + * relative to the caller's snapshot, whereas in read-write mode they are + * relative to a current snapshot). + */ +bool +LargeObjectExists(Oid loid) +{ + Relation pg_lo_meta; + ScanKeyData skey[1]; + SysScanDesc sd; + HeapTuple tuple; + bool retval = false; + + ScanKeyInit(&skey[0], + Anum_pg_largeobject_metadata_oid, + BTEqualStrategyNumber, F_OIDEQ, + ObjectIdGetDatum(loid)); + + pg_lo_meta = table_open(LargeObjectMetadataRelationId, + AccessShareLock); + + sd = systable_beginscan(pg_lo_meta, + LargeObjectMetadataOidIndexId, true, + NULL, 1, skey); + + tuple = systable_getnext(sd); + if (HeapTupleIsValid(tuple)) + retval = true; + + systable_endscan(sd); + + table_close(pg_lo_meta, AccessShareLock); + + return retval; +} |