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/*------------------------------------------------------------------------- * * snapshot.h * POSTGRES snapshot definition * * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * src/include/utils/snapshot.h * *------------------------------------------------------------------------- */ #ifndef SNAPSHOT_H #define SNAPSHOT_H #include "access/htup.h" #include "storage/buf.h" typedef struct SnapshotData *Snapshot; #define InvalidSnapshot ((Snapshot) NULL) /* * We use SnapshotData structures to represent both "regular" (MVCC) * snapshots and "special" snapshots that have non-MVCC semantics. * The specific semantics of a snapshot are encoded by the "satisfies" * function. */ typedef bool (*SnapshotSatisfiesFunc) (HeapTupleHeader tuple, Snapshot snapshot, Buffer buffer); typedef struct SnapshotData { SnapshotSatisfiesFunc satisfies; /* tuple test function */ /* * The remaining fields are used only for MVCC snapshots, and are normally * just zeroes in special snapshots. (But xmin and xmax are used * specially by HeapTupleSatisfiesDirty.) * * An MVCC snapshot can never see the effects of XIDs >= xmax. It can see * the effects of all older XIDs except those listed in the snapshot. xmin * is stored as an optimization to avoid needing to search the XID arrays * for most tuples. */ TransactionId xmin; /* all XID < xmin are visible to me */ TransactionId xmax; /* all XID >= xmax are invisible to me */ TransactionId *xip; /* array of xact IDs in progress */ uint32 xcnt; /* # of xact ids in xip[] */ /* note: all ids in xip[] satisfy xmin <= xip[i] < xmax */ int32 subxcnt; /* # of xact ids in subxip[] */ TransactionId *subxip; /* array of subxact IDs in progress */ bool suboverflowed; /* has the subxip array overflowed? */ bool takenDuringRecovery; /* recovery-shaped snapshot? */ bool copied; /* false if it's a static snapshot */ /* * note: all ids in subxip[] are >= xmin, but we don't bother filtering * out any that are >= xmax */ CommandId curcid; /* in my xact, CID < curcid are visible */ uint32 active_count; /* refcount on ActiveSnapshot stack */ uint32 regd_count; /* refcount on RegisteredSnapshotList */ } SnapshotData; /* * Result codes for HeapTupleSatisfiesUpdate. This should really be in * tqual.h, but we want to avoid including that file elsewhere. */ typedef enum { HeapTupleMayBeUpdated, HeapTupleInvisible, HeapTupleSelfUpdated, HeapTupleUpdated, HeapTupleBeingUpdated } HTSU_Result; #endif /* SNAPSHOT_H */