1 files changed, 74 insertions, 0 deletions
diff --git a/src/backend/utils/time/combocid.c b/src/backend/utils/time/combocid.c
index bfd7d0ad426..cc5409b8803 100644
--- a/src/backend/utils/time/combocid.c
+++ b/src/backend/utils/time/combocid.c
@@ -44,6 +44,7 @@
 #include "miscadmin.h"
 #include "access/htup_details.h"
 #include "access/xact.h"
+#include "storage/shmem.h"
 #include "utils/combocid.h"
 #include "utils/hsearch.h"
 #include "utils/memutils.h"
@@ -286,3 +287,76 @@ GetRealCmax(CommandId combocid)
 	Assert(combocid < usedComboCids);
 	return comboCids[combocid].cmax;
 }
+
+/*
+ * Estimate the amount of space required to serialize the current ComboCID
+ * state.
+ */
+Size
+EstimateComboCIDStateSpace(void)
+{
+	Size		size;
+
+	/* Add space required for saving usedComboCids */
+	size = sizeof(int);
+
+	/* Add space required for saving the combocids key */
+	size = add_size(size, mul_size(sizeof(ComboCidKeyData), usedComboCids));
+
+	return size;
+}
+
+/*
+ * Serialize the ComboCID state into the memory, beginning at start_address.
+ * maxsize should be at least as large as the value returned by
+ * EstimateComboCIDStateSpace.
+ */
+void
+SerializeComboCIDState(Size maxsize, char *start_address)
+{
+	char	   *endptr;
+
+	/* First, we store the number of currently-existing ComboCIDs. */
+	* (int *) start_address = usedComboCids;
+
+	/* If maxsize is too small, throw an error. */
+	endptr = start_address + sizeof(int) +
+		(sizeof(ComboCidKeyData) * usedComboCids);
+	if (endptr < start_address || endptr > start_address + maxsize)
+		elog(ERROR, "not enough space to serialize ComboCID state");
+
+	/* Now, copy the actual cmin/cmax pairs. */
+	memcpy(start_address + sizeof(int), comboCids,
+		   (sizeof(ComboCidKeyData) * usedComboCids));
+}
+
+/*
+ * Read the ComboCID state at the specified address and initialize this
+ * backend with the same ComboCIDs.  This is only valid in a backend that
+ * currently has no ComboCIDs (and only makes sense if the transaction state
+ * is serialized and restored as well).
+ */
+void
+RestoreComboCIDState(char *comboCIDstate)
+{
+	int			num_elements;
+	ComboCidKeyData *keydata;
+	int			i;
+	CommandId	cid;
+
+	Assert(!comboCids && !comboHash);
+
+	/* First, we retrieve the number of ComboCIDs that were serialized. */
+	num_elements = * (int *) comboCIDstate;
+	keydata = (ComboCidKeyData *) (comboCIDstate + sizeof(int));
+
+	/* Use GetComboCommandId to restore each ComboCID. */
+	for (i = 0; i < num_elements; i++)
+	{
+		cid = GetComboCommandId(keydata[i].cmin, keydata[i].cmax);
+
+		/* Verify that we got the expected answer. */
+		if (cid != i)
+			elog(ERROR, "unexpected command ID while restoring combo CIDs");
+	}
+}