Adding upstream version 15.5.upstream/15.5

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 160 insertions, 0 deletions

diff --git a/contrib/old_snapshot/time_mapping.c b/contrib/old_snapshot/time_mapping.c
new file mode 100644
index 0000000..2d8cb74
--- /dev/null
+++ b/contrib/old_snapshot/time_mapping.c
@@ -0,0 +1,160 @@
+/*-------------------------------------------------------------------------
+ *
+ * time_mapping.c
+ *	  time to XID mapping information
+ *
+ * Copyright (c) 2020-2022, PostgreSQL Global Development Group
+ *
+ *	  contrib/old_snapshot/time_mapping.c
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "funcapi.h"
+#include "storage/lwlock.h"
+#include "utils/old_snapshot.h"
+#include "utils/snapmgr.h"
+#include "utils/timestamp.h"
+
+/*
+ * Backend-private copy of the information from oldSnapshotControl which relates
+ * to the time to XID mapping, plus an index so that we can iterate.
+ *
+ * Note that the length of the xid_by_minute array is given by
+ * OLD_SNAPSHOT_TIME_MAP_ENTRIES (which is not a compile-time constant).
+ */
+typedef struct
+{
+	int			current_index;
+	int			head_offset;
+	TimestampTz head_timestamp;
+	int			count_used;
+	TransactionId xid_by_minute[FLEXIBLE_ARRAY_MEMBER];
+} OldSnapshotTimeMapping;
+
+#define NUM_TIME_MAPPING_COLUMNS 3
+
+PG_MODULE_MAGIC;
+PG_FUNCTION_INFO_V1(pg_old_snapshot_time_mapping);
+
+static OldSnapshotTimeMapping *GetOldSnapshotTimeMapping(void);
+static TupleDesc MakeOldSnapshotTimeMappingTupleDesc(void);
+static HeapTuple MakeOldSnapshotTimeMappingTuple(TupleDesc tupdesc,
+												 OldSnapshotTimeMapping *mapping);
+
+/*
+ * SQL-callable set-returning function.
+ */
+Datum
+pg_old_snapshot_time_mapping(PG_FUNCTION_ARGS)
+{
+	FuncCallContext *funcctx;
+	OldSnapshotTimeMapping *mapping;
+
+	if (SRF_IS_FIRSTCALL())
+	{
+		MemoryContext oldcontext;
+
+		funcctx = SRF_FIRSTCALL_INIT();
+		oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
+		mapping = GetOldSnapshotTimeMapping();
+		funcctx->user_fctx = mapping;
+		funcctx->tuple_desc = MakeOldSnapshotTimeMappingTupleDesc();
+		MemoryContextSwitchTo(oldcontext);
+	}
+
+	funcctx = SRF_PERCALL_SETUP();
+	mapping = (OldSnapshotTimeMapping *) funcctx->user_fctx;
+
+	while (mapping->current_index < mapping->count_used)
+	{
+		HeapTuple	tuple;
+
+		tuple = MakeOldSnapshotTimeMappingTuple(funcctx->tuple_desc, mapping);
+		++mapping->current_index;
+		SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
+	}
+
+	SRF_RETURN_DONE(funcctx);
+}
+
+/*
+ * Get the old snapshot time mapping data from shared memory.
+ */
+static OldSnapshotTimeMapping *
+GetOldSnapshotTimeMapping(void)
+{
+	OldSnapshotTimeMapping *mapping;
+
+	mapping = palloc(offsetof(OldSnapshotTimeMapping, xid_by_minute)
+					 + sizeof(TransactionId) * OLD_SNAPSHOT_TIME_MAP_ENTRIES);
+	mapping->current_index = 0;
+
+	LWLockAcquire(OldSnapshotTimeMapLock, LW_SHARED);
+	mapping->head_offset = oldSnapshotControl->head_offset;
+	mapping->head_timestamp = oldSnapshotControl->head_timestamp;
+	mapping->count_used = oldSnapshotControl->count_used;
+	for (int i = 0; i < OLD_SNAPSHOT_TIME_MAP_ENTRIES; ++i)
+		mapping->xid_by_minute[i] = oldSnapshotControl->xid_by_minute[i];
+	LWLockRelease(OldSnapshotTimeMapLock);
+
+	return mapping;
+}
+
+/*
+ * Build a tuple descriptor for the pg_old_snapshot_time_mapping() SRF.
+ */
+static TupleDesc
+MakeOldSnapshotTimeMappingTupleDesc(void)
+{
+	TupleDesc	tupdesc;
+
+	tupdesc = CreateTemplateTupleDesc(NUM_TIME_MAPPING_COLUMNS);
+
+	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "array_offset",
+					   INT4OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "end_timestamp",
+					   TIMESTAMPTZOID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 3, "newest_xmin",
+					   XIDOID, -1, 0);
+
+	return BlessTupleDesc(tupdesc);
+}
+
+/*
+ * Convert one entry from the old snapshot time mapping to a HeapTuple.
+ */
+static HeapTuple
+MakeOldSnapshotTimeMappingTuple(TupleDesc tupdesc, OldSnapshotTimeMapping *mapping)
+{
+	Datum		values[NUM_TIME_MAPPING_COLUMNS];
+	bool		nulls[NUM_TIME_MAPPING_COLUMNS];
+	int			array_position;
+	TimestampTz timestamp;
+
+	/*
+	 * Figure out the array position corresponding to the current index.
+	 *
+	 * Index 0 means the oldest entry in the mapping, which is stored at
+	 * mapping->head_offset. Index 1 means the next-oldest entry, which is a
+	 * the following index, and so on. We wrap around when we reach the end of
+	 * the array.
+	 */
+	array_position = (mapping->head_offset + mapping->current_index)
+		% OLD_SNAPSHOT_TIME_MAP_ENTRIES;
+
+	/*
+	 * No explicit timestamp is stored for any entry other than the oldest
+	 * one, but each entry corresponds to 1-minute period, so we can just add.
+	 */
+	timestamp = TimestampTzPlusMilliseconds(mapping->head_timestamp,
+											mapping->current_index * 60000);
+
+	/* Initialize nulls and values arrays. */
+	memset(nulls, 0, sizeof(nulls));
+	values[0] = Int32GetDatum(array_position);
+	values[1] = TimestampTzGetDatum(timestamp);
+	values[2] = TransactionIdGetDatum(mapping->xid_by_minute[array_position]);
+
+	return heap_form_tuple(tupdesc, values, nulls);
+}