diff --git a/src/backend/utils/adt/array_userfuncs.c b/src/backend/utils/adt/array_userfuncs.c
index cb7a6b6d010..ae698482899 100644
--- a/src/backend/utils/adt/array_userfuncs.c
+++ b/src/backend/utils/adt/array_userfuncs.c
@@ -13,12 +13,33 @@
 #include "postgres.h"
 
 #include "catalog/pg_type.h"
+#include "libpq/pqformat.h"
 #include "common/int.h"
 #include "utils/array.h"
+#include "utils/datum.h"
 #include "utils/builtins.h"
 #include "utils/lsyscache.h"
 #include "utils/typcache.h"
 
+/*
+ * DeserialIOData
+ *		Used for caching type data in array deserial function
+ */
+typedef struct DeserialIOData
+{
+	Oid		typreceive;
+	Oid		typioparam;
+} DeserialIOData;
+
+/*
+ * SerialIOData
+ *		Used for caching type data in array serial function
+ */
+typedef struct SerialIOData
+{
+	Oid			typsend;
+	bool		typisvarlena;
+} SerialIOData;
 
 static Datum array_position_common(FunctionCallInfo fcinfo);
 
@@ -498,6 +519,267 @@ array_agg_transfn(PG_FUNCTION_ARGS)
 	PG_RETURN_POINTER(state);
 }
 
+Datum
+array_agg_combine(PG_FUNCTION_ARGS)
+{
+	ArrayBuildState *state1;
+	ArrayBuildState *state2;
+	MemoryContext agg_context;
+	MemoryContext old_context;
+	int		i;
+
+	if (!AggCheckCallContext(fcinfo, &agg_context))
+		elog(ERROR, "aggregate function called in non-aggregate context");
+
+	state1 = PG_ARGISNULL(0) ? NULL : (ArrayBuildState *) PG_GETARG_POINTER(0);
+	state2 = PG_ARGISNULL(1) ? NULL : (ArrayBuildState *) PG_GETARG_POINTER(1);
+
+	if (state2 == NULL)
+		PG_RETURN_POINTER(state1);
+
+	/* Manually copy all fields from state2 to state1 */
+	if (state1 == NULL)
+	{
+		old_context = MemoryContextSwitchTo(agg_context);
+
+		state1 = initArrayResultWithSize(state2->element_type, agg_context,
+										 false, state2->alen);
+
+		state1->nelems = state2->nelems;
+
+		for (i = 0; i < state2->nelems; i++)
+			state1->dvalues[i] = datumCopy(state2->dvalues[i],
+										   state1->typbyval, state1->typlen);
+
+		memcpy(state1->dnulls, state2->dnulls, sizeof(bool) * state2->nelems);
+
+		state1->nelems = state2->nelems;
+
+		MemoryContextSwitchTo(old_context);
+
+		PG_RETURN_POINTER(state1);
+	}
+
+	/* We only need to combine the two states if state2 has any elements */
+	else if (state2->nelems > 0)
+	{
+		int reqsize = state1->nelems + state2->nelems;
+		MemoryContext oldContext = MemoryContextSwitchTo(state1->mcontext);
+
+		/*
+		 * If there's not enough space in state1 then we'll need to reallocate
+		 * more.
+		 */
+		if (state1->alen < reqsize)
+		{
+			/* Use a power of 2 size rather than allocating just reqsize */
+			while (state1->alen < reqsize)
+				state1->alen *= 2;
+
+			state1->dvalues = (Datum *) repalloc(state1->dvalues, state1->alen * sizeof(Datum));
+			state1->dnulls = (bool *) repalloc(state1->dnulls, state1->alen * sizeof(bool));
+		}
+
+		/* Copy in the state2 elements to the end of the state1 arrays */
+		for (i = 0; i < state2->nelems; i++)
+			state1->dvalues[i + state1->nelems] = datumCopy(state2->dvalues[i],
+											state1->typbyval, state1->typlen);
+
+		memcpy(&state1->dnulls[state1->nelems], state2->dnulls, sizeof(bool) * state2->nelems);
+
+		state1->nelems = reqsize;
+
+		MemoryContextSwitchTo(oldContext);
+	}
+
+	PG_RETURN_POINTER(state1);
+}
+
+/*
+ * array_agg_serialize
+ *		Serialize ArrayBuildState into bytea.
+ */
+Datum
+array_agg_serialize(PG_FUNCTION_ARGS)
+{
+	ArrayBuildState *state;
+	StringInfoData buf;
+	bytea	   *result;
+
+	/* cannot be called directly because of internal-type argument */
+	Assert(AggCheckCallContext(fcinfo, NULL));
+
+	state = (ArrayBuildState *) PG_GETARG_POINTER(0);
+
+	pq_begintypsend(&buf);
+
+	/*
+	 * element_type. Putting this first is more convenient in deserialization
+	 */
+	pq_sendint32(&buf, state->element_type);
+
+	/*
+	 * nelems -- send first so we know how large to make the dvalues and
+	 * dnulls array during deserialization.
+	 */
+	pq_sendint64(&buf, state->nelems);
+
+	/* alen can be decided during deserialization */
+
+	/* typlen */
+	pq_sendint16(&buf, state->typlen);
+
+	/* typbyval */
+	pq_sendbyte(&buf, state->typbyval);
+
+	/* typalign */
+	pq_sendbyte(&buf, state->typalign);
+
+
+	/*
+	 * dvalues -- this is very simple when the value type is byval, we can
+	 * simply just send the Datums over, however, for non-byval types we must
+	 * work a little harder.
+	 */
+	if (state->typbyval)
+		pq_sendbytes(&buf, (char *) state->dvalues, sizeof(Datum) * state->nelems);
+	else
+	{
+		SerialIOData *iodata;
+		bytea	   *outputbytes;
+		int			i;
+
+		/*
+		 * To avoid having to constantly make calls to getTypeBinaryOutputInfo
+		 * we'll cache that information in fn_extra for the next call.  Let's
+		 * see if we've done that already...
+		 */
+		if (fcinfo->flinfo->fn_extra)
+			iodata = (SerialIOData *) fcinfo->flinfo->fn_extra;
+		else
+		{
+			fcinfo->flinfo->fn_extra = iodata =
+								MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
+												   sizeof(SerialIOData));
+			getTypeBinaryOutputInfo(state->element_type, &iodata->typsend,
+									&iodata->typisvarlena);
+		}
+
+		for (i = 0; i < state->nelems; i++)
+		{
+			outputbytes = OidSendFunctionCall(iodata->typsend, state->dvalues[i]);
+			pq_sendint32(&buf, VARSIZE(outputbytes) - VARHDRSZ);
+			pq_sendbytes(&buf, VARDATA(outputbytes),
+							VARSIZE(outputbytes) - VARHDRSZ);
+		}
+	}
+
+	/* dnulls */
+	pq_sendbytes(&buf, (char *) state->dnulls, sizeof(bool) * state->nelems);
+
+	result = pq_endtypsend(&buf);
+
+	PG_RETURN_BYTEA_P(result);
+}
+
+Datum
+array_agg_deserialize(PG_FUNCTION_ARGS)
+{
+	bytea		   *sstate;
+	ArrayBuildState *result;
+	StringInfoData	buf;
+	Oid				element_type;
+	int64			nelems;
+	const char	   *temp;
+
+	if (!AggCheckCallContext(fcinfo, NULL))
+		elog(ERROR, "aggregate function called in non-aggregate context");
+
+	sstate = PG_GETARG_BYTEA_PP(0);
+
+	/*
+	 * Copy the bytea into a StringInfo so that we can "receive" it using the
+	 * standard recv-function infrastructure.
+	 */
+	initStringInfo(&buf);
+	appendBinaryStringInfo(&buf,
+						   VARDATA_ANY(sstate), VARSIZE_ANY_EXHDR(sstate));
+
+	/* element_type */
+	element_type = pq_getmsgint(&buf, 4);
+
+	/* nelems */
+	nelems = pq_getmsgint64(&buf);
+
+	result = initArrayResultWithSize(element_type, CurrentMemoryContext,
+									 false, nelems);
+
+	result->nelems = nelems;
+
+	/* typlen */
+	result->typlen = pq_getmsgint(&buf, 2);
+
+	/* typbyval */
+	result->typbyval = pq_getmsgbyte(&buf);
+
+	/* typalign */
+	result->typalign = pq_getmsgbyte(&buf);
+
+	/*
+	 * dvalues -- this is very simple when the value type is byval, we can
+	 * simply just get all the Datums at once, however, for non-byval types we
+	 * must work a little harder.
+	 */
+	if (result->typbyval)
+	{
+		temp = pq_getmsgbytes(&buf, sizeof(Datum) * nelems);
+		memcpy(result->dvalues, temp, sizeof(Datum) * nelems);
+	}
+	else
+	{
+		DeserialIOData *iodata;
+		int		i;
+
+		/*
+		 * To avoid having to constantly make calls to getTypeBinaryInputInfo
+		 * we'll cache that information in fn_extra for the next call.  Let's
+		 * see if we've done that already...
+		 */
+		if (fcinfo->flinfo->fn_extra)
+			iodata = (DeserialIOData *) fcinfo->flinfo->fn_extra;
+		else
+		{
+			fcinfo->flinfo->fn_extra = iodata =
+								MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
+												   sizeof(DeserialIOData));
+			getTypeBinaryInputInfo(element_type, &iodata->typreceive,
+								   &iodata->typioparam);
+		}
+
+		for (i = 0; i < nelems; i++)
+		{
+			StringInfoData tmp;
+			tmp.cursor = 0;
+			tmp.maxlen = tmp.len = pq_getmsgint(&buf, 4);
+			tmp.data = (char *) pq_getmsgbytes(&buf, tmp.len);
+
+			result->dvalues[i] = OidReceiveFunctionCall(iodata->typreceive,
+														&tmp,
+														iodata->typioparam,
+														-1);
+		}
+	}
+
+	/* dnulls */
+	temp = pq_getmsgbytes(&buf, sizeof(bool) * nelems);
+	memcpy(result->dnulls, temp, sizeof(bool) * nelems);
+
+	pq_getmsgend(&buf);
+	pfree(buf.data);
+
+	PG_RETURN_POINTER(result);
+}
+
 Datum
 array_agg_finalfn(PG_FUNCTION_ARGS)
 {
@@ -577,6 +859,295 @@ array_agg_array_transfn(PG_FUNCTION_ARGS)
 	PG_RETURN_POINTER(state);
 }
 
+Datum
+array_agg_array_combine(PG_FUNCTION_ARGS)
+{
+	ArrayBuildStateArr *state1;
+	ArrayBuildStateArr *state2;
+	MemoryContext agg_context;
+	MemoryContext old_context;
+
+	if (!AggCheckCallContext(fcinfo, &agg_context))
+		elog(ERROR, "aggregate function called in non-aggregate context");
+
+	state1 = PG_ARGISNULL(0) ? NULL : (ArrayBuildStateArr *) PG_GETARG_POINTER(0);
+	state2 = PG_ARGISNULL(1) ? NULL : (ArrayBuildStateArr *) PG_GETARG_POINTER(1);
+
+	if (state2 == NULL)
+		PG_RETURN_POINTER(state1);
+
+	/* Manually copy all fields from state2 to state1 */
+	if (state1 == NULL)
+	{
+		old_context = MemoryContextSwitchTo(agg_context);
+
+		state1 = initArrayResultArr(state2->array_type, InvalidOid,
+									agg_context, false);
+
+		state1->abytes = state2->abytes;
+		state1->data = (char *) palloc(state1->abytes);
+
+		if (state2->nullbitmap)
+		{
+			int size = (state2->aitems + 7) / 8;
+			state1->nullbitmap = (bits8 *) palloc(size);
+			memcpy(state1->nullbitmap, state2->nullbitmap, size);
+		}
+
+		memcpy(state1->data, state2->data, state2->nbytes);
+		state1->nbytes = state2->nbytes;
+		state1->aitems = state2->aitems;
+		state1->nitems = state2->nitems;
+		state1->ndims = state2->ndims;
+		memcpy(state1->dims, state2->dims, sizeof(state2->dims));
+		memcpy(state1->lbs, state2->lbs, sizeof(state2->lbs));
+		state1->array_type = state2->array_type;
+		state1->element_type = state2->element_type;
+
+		MemoryContextSwitchTo(old_context);
+
+		PG_RETURN_POINTER(state1);
+	}
+
+	/* We only need to combine the two states if state2 has any items */
+	else if (state2->nitems > 0)
+	{
+		MemoryContext oldContext;
+		int reqsize = state1->nbytes + state2->nbytes;
+		int i;
+
+		/*
+		 * Check the states are compatible with each other.  Ensure we use the
+		 * same error messages that are listed in accumArrayResultArr so that
+		 * the same error is shown as would have been if we'd not used the
+		 * combine function for the aggregation.
+		 */
+		if (state1->ndims != state2->ndims)
+			ereport(ERROR,
+					(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
+					 errmsg("cannot accumulate arrays of different dimensionality")));
+
+		/* Check dimensions match ignoring the first dimension. */
+		for (i = 1; i < state1->ndims; i++)
+		{
+			if (state1->dims[i] != state2->dims[i] || state1->lbs[i] != state2->lbs[i])
+				ereport(ERROR,
+						(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
+						 errmsg("cannot accumulate arrays of different dimensionality")));
+		}
+
+
+		oldContext = MemoryContextSwitchTo(state1->mcontext);
+
+		/*
+		 * If there's not enough space in state1 then we'll need to reallocate
+		 * more.
+		 */
+		if (state1->abytes < reqsize)
+		{
+			/* use a power of 2 size rather than allocating just reqsize */
+			while (state1->abytes < reqsize)
+				state1->abytes *= 2;
+
+			state1->data = (char *) repalloc(state1->data, state1->abytes);
+		}
+
+		if (state2->nullbitmap)
+		{
+			int			newnitems = state1->nitems + state2->nitems;
+
+			if (state1->nullbitmap == NULL)
+			{
+				/*
+				 * First input with nulls; we must retrospectively handle any
+				 * previous inputs by marking all their items non-null.
+				 */
+				state1->aitems = 256;
+				while (state1->aitems <= newnitems)
+					state1->aitems *= 2;
+				state1->nullbitmap = (bits8 *) palloc((state1->aitems + 7) / 8);
+				array_bitmap_copy(state1->nullbitmap, 0,
+								  NULL, 0,
+								  state1->nitems);
+			}
+			else if (newnitems > state1->aitems)
+			{
+				int newaitems = state1->aitems + state2->aitems;
+
+				while (state1->aitems < newaitems)
+					state1->aitems *= 2;
+
+				state1->nullbitmap = (bits8 *)
+					repalloc(state1->nullbitmap, (state1->aitems + 7) / 8);
+			}
+			array_bitmap_copy(state1->nullbitmap, state1->nitems,
+							  state2->nullbitmap, 0,
+							  state2->nitems);
+		}
+
+		memcpy(state1->data + state1->nbytes, state2->data, state2->nbytes);
+		state1->nbytes += state2->nbytes;
+		state1->nitems += state2->nitems;
+
+		state1->dims[0] += state2->dims[0];
+		/* remaing dims already match, per test above */
+
+		Assert(state1->array_type == state2->array_type);
+		Assert(state1->element_type = state2->element_type);
+
+		MemoryContextSwitchTo(oldContext);
+	}
+
+	PG_RETURN_POINTER(state1);
+}
+
+/*
+ * array_agg_array_serialize
+ *		Serialize ArrayBuildStateArr into bytea.
+ */
+Datum
+array_agg_array_serialize(PG_FUNCTION_ARGS)
+{
+	ArrayBuildStateArr *state;
+	StringInfoData buf;
+	bytea	   *result;
+
+	/* cannot be called directly because of internal-type argument */
+	Assert(AggCheckCallContext(fcinfo, NULL));
+
+	state = (ArrayBuildStateArr *) PG_GETARG_POINTER(0);
+
+	pq_begintypsend(&buf);
+
+	/*
+	 * element_type. Putting this first is more convenient in deserialization
+	 * so that we can init the new state sooner.
+	 */
+	pq_sendint32(&buf, state->element_type);
+
+	/* array_type */
+	pq_sendint32(&buf, state->array_type);
+
+	/* nbytes */
+	pq_sendint32(&buf, state->nbytes);
+
+	/* data */
+	pq_sendbytes(&buf, state->data, state->nbytes);
+
+	/* abytes */
+	pq_sendint32(&buf, state->abytes);
+
+	/* aitems */
+	pq_sendint32(&buf, state->aitems);
+
+	/* nullbitmap */
+	if (state->nullbitmap)
+	{
+		Assert(state->aitems > 0);
+		pq_sendbytes(&buf, (char *) state->nullbitmap, (state->aitems + 7) / 8);
+	}
+
+	/* nitems */
+	pq_sendint32(&buf, state->nitems);
+
+	/* ndims */
+	pq_sendint32(&buf, state->ndims);
+
+	/* dims: XXX or should we just send ndim's worth? */
+	pq_sendbytes(&buf, (char *) state->dims, sizeof(state->dims));
+
+	/* lbs */
+	pq_sendbytes(&buf, (char *) state->lbs, sizeof(state->lbs));
+
+	result = pq_endtypsend(&buf);
+
+	PG_RETURN_BYTEA_P(result);
+}
+
+Datum
+array_agg_array_deserialize(PG_FUNCTION_ARGS)
+{
+	bytea		   *sstate;
+	ArrayBuildStateArr *result;
+	StringInfoData	buf;
+	Oid				element_type;
+	Oid				array_type;
+	int				nbytes;
+	const char	   *temp;
+
+	/* cannot be called directly because of internal-type argument */
+	Assert(AggCheckCallContext(fcinfo, NULL));
+
+	sstate = PG_GETARG_BYTEA_PP(0);
+
+	/*
+	 * Copy the bytea into a StringInfo so that we can "receive" it using the
+	 * standard recv-function infrastructure.
+	 */
+	initStringInfo(&buf);
+	appendBinaryStringInfo(&buf,
+						   VARDATA_ANY(sstate), VARSIZE_ANY_EXHDR(sstate));
+
+	/* element_type */
+	element_type = pq_getmsgint(&buf, 4);
+
+	/* array_type */
+	array_type = pq_getmsgint(&buf, 4);
+
+	/* nbytes */
+	nbytes = pq_getmsgint(&buf, 4);
+
+	result  = initArrayResultArr(array_type, element_type,
+								 CurrentMemoryContext, false);
+
+	result->abytes = 1024;
+	while (result->abytes < nbytes)
+		result->abytes *= 2;
+
+	result->data = (char *) palloc(result->abytes);
+
+	/* data */
+	temp = pq_getmsgbytes(&buf, nbytes);
+	memcpy(result->data, temp, nbytes);
+	result->nbytes = nbytes;
+
+	/* abytes */
+	result->abytes = pq_getmsgint(&buf, 4);
+
+	/* aitems: might be 0 */
+	result->aitems = pq_getmsgint(&buf, 4);
+
+	/* nullbitmap */
+	if (result->aitems > 0)
+	{
+		int size = (result->aitems + 7) / 8;
+		result->nullbitmap = (bits8 *) palloc(size);
+		temp = pq_getmsgbytes(&buf, size);
+		memcpy(result->nullbitmap, temp, size);
+	}
+	else
+		result->nullbitmap = NULL;
+
+	/* nitems */
+	result->nitems = pq_getmsgint(&buf, 4);
+
+	/* ndims */
+	result->ndims = pq_getmsgint(&buf, 4);
+
+	/* dims */
+	temp = pq_getmsgbytes(&buf, sizeof(result->dims));
+	memcpy(result->dims, temp, sizeof(result->dims));
+
+	/* lbs */
+	temp = pq_getmsgbytes(&buf, sizeof(result->lbs));
+	memcpy(result->lbs, temp, sizeof(result->lbs));
+
+	pq_getmsgend(&buf);
+	pfree(buf.data);
+
+	PG_RETURN_POINTER(result);
+}
+
 Datum
 array_agg_array_finalfn(PG_FUNCTION_ARGS)
 {
diff --git a/src/backend/utils/adt/arrayfuncs.c b/src/backend/utils/adt/arrayfuncs.c
index 0cbdbe5587e..063182326de 100644
--- a/src/backend/utils/adt/arrayfuncs.c
+++ b/src/backend/utils/adt/arrayfuncs.c
@@ -5001,6 +5001,19 @@ array_insert_slice(ArrayType *destArray,
  */
 ArrayBuildState *
 initArrayResult(Oid element_type, MemoryContext rcontext, bool subcontext)
+{
+	return initArrayResultWithSize(element_type, rcontext, subcontext,
+								   subcontext ? 64 : 8);
+}
+
+/*
+ * initArrayResultWithSize
+ *		As initArrayResult, but allow the initial size of the allocated arrays
+ *		to be specified.
+ */
+ArrayBuildState *
+initArrayResultWithSize(Oid element_type, MemoryContext rcontext,
+						bool subcontext, int initsize)
 {
 	ArrayBuildState *astate;
 	MemoryContext arr_context = rcontext;
@@ -5015,7 +5028,7 @@ initArrayResult(Oid element_type, MemoryContext rcontext, bool subcontext)
 		MemoryContextAlloc(arr_context, sizeof(ArrayBuildState));
 	astate->mcontext = arr_context;
 	astate->private_cxt = subcontext;
-	astate->alen = (subcontext ? 64 : 8);	/* arbitrary starting array size */
+	astate->alen = initsize;
 	astate->dvalues = (Datum *)
 		MemoryContextAlloc(arr_context, astate->alen * sizeof(Datum));
 	astate->dnulls = (bool *)
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 4346410d5a9..e047ba07bbf 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -458,13 +458,30 @@ bytea_string_agg_transfn(PG_FUNCTION_ARGS)
 	{
 		bytea	   *value = PG_GETARG_BYTEA_PP(1);
 
-		/* On the first time through, we ignore the delimiter. */
+		/*
+		 * It's important that we store the delimiter text for all aggregated
+		 * items, even the first one, which at first thought you might think
+		 * could just be discarded.  The reason for this is that if this
+		 * function is being called from a parallel worker, then we'll need
+		 * the first delimiter in order to properly combine the partially
+		 * aggregated state with the states coming from other workers.  In the
+		 * final output, the first delimiter will be stripped off of the final
+		 * aggregate state, but in order to know where the actual first data
+		 * is we must store the position of the first data value somewhere.
+		 * Conveniently, StringInfo has a cursor property which can be used
+		 * to serve our needs here.
+		 */
 		if (state == NULL)
+		{
 			state = makeStringAggState(fcinfo);
-		else if (!PG_ARGISNULL(2))
+
+			if (!PG_ARGISNULL(2))
+				state->cursor = VARSIZE_ANY_EXHDR(PG_GETARG_BYTEA_PP(2));
+		}
+
+		if (!PG_ARGISNULL(2))
 		{
 			bytea	   *delim = PG_GETARG_BYTEA_PP(2);
-
 			appendBinaryStringInfo(state, VARDATA_ANY(delim), VARSIZE_ANY_EXHDR(delim));
 		}
 
@@ -478,6 +495,69 @@ bytea_string_agg_transfn(PG_FUNCTION_ARGS)
 	PG_RETURN_POINTER(state);
 }
 
+Datum
+bytea_string_agg_serialize(PG_FUNCTION_ARGS)
+{
+	StringInfo state;
+	StringInfoData buf;
+	bytea	   *result;
+
+	/* cannot be called directly because of internal-type argument */
+	Assert(AggCheckCallContext(fcinfo, NULL));
+
+	state = (StringInfo) PG_GETARG_POINTER(0);
+
+	pq_begintypsend(&buf);
+
+	/*
+	 * cursor -- we must send this position so we can properly skip past the
+	 * delimiter for the first aggregated string
+	 */
+	pq_sendint(&buf, state->cursor, 4);
+
+	pq_sendbytes(&buf, state->data, state->len);
+
+	result = pq_endtypsend(&buf);
+
+	PG_RETURN_BYTEA_P(result);
+}
+
+Datum
+bytea_string_agg_deserialize(PG_FUNCTION_ARGS)
+{
+	bytea	   *sstate;
+	StringInfo	result;
+	StringInfoData buf;
+	char	   *temp;
+
+	/* cannot be called directly because of internal-type argument */
+	Assert(AggCheckCallContext(fcinfo, NULL));
+
+	sstate = PG_GETARG_BYTEA_PP(0);
+
+	/*
+	 * Copy the bytea into a StringInfo so that we can "receive" it using the
+	 * standard recv-function infrastructure.
+	 */
+	initStringInfo(&buf);
+	appendBinaryStringInfo(&buf,
+						   VARDATA_ANY(sstate), VARSIZE_ANY_EXHDR(sstate));
+
+	result = makeStringAggState(fcinfo);
+
+	/* cursor */
+	result->cursor = pq_getmsgint(&buf, 4);
+
+	/* data */
+	temp = (char *) pq_getmsgbytes(&buf, VARSIZE_ANY_EXHDR(sstate) - 4);
+	appendBinaryStringInfo(result, temp, VARSIZE_ANY_EXHDR(sstate) - 4);
+
+	pq_getmsgend(&buf);
+	pfree(buf.data);
+
+	PG_RETURN_POINTER(result);
+}
+
 Datum
 bytea_string_agg_finalfn(PG_FUNCTION_ARGS)
 {
@@ -492,9 +572,10 @@ bytea_string_agg_finalfn(PG_FUNCTION_ARGS)
 	{
 		bytea	   *result;
 
-		result = (bytea *) palloc(state->len + VARHDRSZ);
-		SET_VARSIZE(result, state->len + VARHDRSZ);
-		memcpy(VARDATA(result), state->data, state->len);
+		result = (bytea *) palloc(state->len - state->cursor + VARHDRSZ);
+		SET_VARSIZE(result, state->len - state->cursor + VARHDRSZ);
+		memcpy(VARDATA(result), &state->data[state->cursor],
+			   state->len - state->cursor);
 		PG_RETURN_BYTEA_P(result);
 	}
 	else
@@ -4656,10 +4737,28 @@ string_agg_transfn(PG_FUNCTION_ARGS)
 	/* Append the value unless null. */
 	if (!PG_ARGISNULL(1))
 	{
-		/* On the first time through, we ignore the delimiter. */
+		/*
+		 * It's important that we store the delimiter text for all aggregated
+		 * items, even the first one, which at first thought you might think
+		 * could just be discarded.  The reason for this is that if this
+		 * function is being called from a parallel worker, then we'll need
+		 * the first delimiter in order to properly combine the partially
+		 * aggregated state with the states coming from other workers.  In the
+		 * final output, the first delimiter will be stripped off of the final
+		 * aggregate state, but in order to know where the actual first data
+		 * is we must store the position of the first data value somewhere.
+		 * Conveniently, StringInfo has a cursor property which can be used
+		 * to serve our needs here.
+		 */
 		if (state == NULL)
+		{
 			state = makeStringAggState(fcinfo);
-		else if (!PG_ARGISNULL(2))
+
+			if (!PG_ARGISNULL(2))
+				state->cursor = VARSIZE_ANY_EXHDR(PG_GETARG_TEXT_PP(2));
+		}
+
+		if (!PG_ARGISNULL(2))
 			appendStringInfoText(state, PG_GETARG_TEXT_PP(2));	/* delimiter */
 
 		appendStringInfoText(state, PG_GETARG_TEXT_PP(1));	/* value */
@@ -4672,6 +4771,108 @@ string_agg_transfn(PG_FUNCTION_ARGS)
 	PG_RETURN_POINTER(state);
 }
 
+/*
+ * string_agg_combine
+ *		Aggregate combine function for string_agg(text) and string_agg(bytea)
+ */
+Datum
+string_agg_combine(PG_FUNCTION_ARGS)
+{
+	StringInfo state1;
+	StringInfo state2;
+	MemoryContext agg_context;
+
+	if (!AggCheckCallContext(fcinfo, &agg_context))
+		elog(ERROR, "aggregate function called in non-aggregate context");
+
+	state1 = PG_ARGISNULL(0) ? NULL : (StringInfo) PG_GETARG_POINTER(0);
+	state2 = PG_ARGISNULL(1) ? NULL : (StringInfo) PG_GETARG_POINTER(1);
+
+	if (state2 == NULL)
+		PG_RETURN_POINTER(state1);
+
+	if (state1 == NULL)
+	{
+		MemoryContext old_context;
+
+		old_context = MemoryContextSwitchTo(agg_context);
+		state1 = makeStringAggState(fcinfo);
+
+		/* The cursor marks the start of the actual data */
+		state1->cursor = state2->cursor;
+
+		appendBinaryStringInfo(state1, state2->data, state2->len);
+
+		MemoryContextSwitchTo(old_context);
+	}
+	else if (state2->len > 0)
+		appendBinaryStringInfo(state1, state2->data, state2->len);
+
+	PG_RETURN_POINTER(state1);
+}
+
+Datum
+string_agg_serialize(PG_FUNCTION_ARGS)
+{
+	StringInfo state;
+	StringInfoData buf;
+	bytea	   *result;
+
+	/* cannot be called directly because of internal-type argument */
+	Assert(AggCheckCallContext(fcinfo, NULL));
+
+	state = (StringInfo) PG_GETARG_POINTER(0);
+
+	pq_begintypsend(&buf);
+
+	/*
+	 * cursor -- we must send this position so we can properly skip past the
+	 * delimiter for the first aggregated string
+	 */
+	pq_sendint(&buf, state->cursor, 4);
+
+	pq_sendtext(&buf, state->data, state->len);
+
+	result = pq_endtypsend(&buf);
+
+	PG_RETURN_BYTEA_P(result);
+}
+
+Datum
+string_agg_deserialize(PG_FUNCTION_ARGS)
+{
+	bytea	   *sstate;
+	StringInfo	result;
+	StringInfoData buf;
+
+	/* cannot be called directly because of internal-type argument */
+	Assert(AggCheckCallContext(fcinfo, NULL));
+
+	sstate = PG_GETARG_BYTEA_PP(0);
+
+	/*
+	 * Copy the bytea into a StringInfo so that we can "receive" it using the
+	 * standard recv-function infrastructure.
+	 */
+	initStringInfo(&buf);
+	appendBinaryStringInfo(&buf,
+						   VARDATA_ANY(sstate), VARSIZE_ANY_EXHDR(sstate));
+
+	result = makeStringAggState(fcinfo);
+
+	/* cursor */
+	result->cursor = pq_getmsgint(&buf, 4);
+
+	/* data: pq_getmsgtext will allocate memory in the required context */
+	result->data = pq_getmsgtext(&buf, VARSIZE_ANY_EXHDR(sstate) - 4,
+								 &result->len);
+
+	pq_getmsgend(&buf);
+	pfree(buf.data);
+
+	PG_RETURN_POINTER(result);
+}
+
 Datum
 string_agg_finalfn(PG_FUNCTION_ARGS)
 {
@@ -4682,8 +4883,13 @@ string_agg_finalfn(PG_FUNCTION_ARGS)
 
 	state = PG_ARGISNULL(0) ? NULL : (StringInfo) PG_GETARG_POINTER(0);
 
+	/*
+	 * Return the text removing the first delimiter text as marked by the
+	 * cursor.
+	 */
 	if (state != NULL)
-		PG_RETURN_TEXT_P(cstring_to_text_with_len(state->data, state->len));
+		PG_RETURN_TEXT_P(cstring_to_text_with_len(&state->data[state->cursor],
+						 state->len - state->cursor));
 	else
 		PG_RETURN_NULL();
 }
diff --git a/src/include/catalog/pg_aggregate.h b/src/include/catalog/pg_aggregate.h
index 125bb5b479d..73f36a0d982 100644
--- a/src/include/catalog/pg_aggregate.h
+++ b/src/include/catalog/pg_aggregate.h
@@ -300,14 +300,14 @@ DATA(insert ( 2243	n 0 bitor		-				bitor	-	-	-				-				-				f f r r 0	1560	0	0
 DATA(insert ( 2901	n 0 xmlconcat2	-				-		-	-	-				-				-				f f r r 0	142		0	0		0	_null_ _null_ ));
 
 /* array */
-DATA(insert ( 2335	n 0 array_agg_transfn		array_agg_finalfn		-	-	-	-		-				-				t f r r 0	2281	0	0		0	_null_ _null_ ));
-DATA(insert ( 4053	n 0 array_agg_array_transfn array_agg_array_finalfn -	-	-	-		-				-				t f r r 0	2281	0	0		0	_null_ _null_ ));
+DATA(insert ( 2335	n 0 array_agg_transfn		array_agg_finalfn		array_agg_combine		array_agg_serialize			array_agg_deserialize		-		-				-				t f r r 0	2281	0	0		0	_null_ _null_ ));
+DATA(insert ( 4053	n 0 array_agg_array_transfn array_agg_array_finalfn array_agg_array_combine	array_agg_array_serialize	array_agg_array_deserialize	-		-				-				t f r r 0	2281	0	0		0	_null_ _null_ ));
 
 /* text */
-DATA(insert ( 3538	n 0 string_agg_transfn	string_agg_finalfn	-	-	-	-				-				-				f f r r 0	2281	0	0		0	_null_ _null_ ));
+DATA(insert ( 3538	n 0 string_agg_transfn	string_agg_finalfn	string_agg_combine	string_agg_serialize	string_agg_deserialize	-				-				-				f f r r 0	2281	0	0		0	_null_ _null_ ));
 
 /* bytea */
-DATA(insert ( 3545	n 0 bytea_string_agg_transfn	bytea_string_agg_finalfn	-	-	-	-				-				-		f f r r 0	2281	0	0		0	_null_ _null_ ));
+DATA(insert ( 3545	n 0 bytea_string_agg_transfn	bytea_string_agg_finalfn	string_agg_combine	bytea_string_agg_serialize	bytea_string_agg_deserialize	-				-				-		f f r r 0	2281	0	0		0	_null_ _null_ ));
 
 /* json */
 DATA(insert ( 3175	n 0 json_agg_transfn	json_agg_finalfn			-	-	-	-				-				-				f f r r 0	2281	0	0		0	_null_ _null_ ));
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index 0fdb42f6397..6efd38fe452 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -942,12 +942,24 @@ DATA(insert OID = 3168 (  array_replace    PGNSP PGUID 12 1 0 0 0 f f f f f i s
 DESCR("replace any occurrences of an element in an array");
 DATA(insert OID = 2333 (  array_agg_transfn   PGNSP PGUID 12 1 0 0 0 f f f f f i s 2 0 2281 "2281 2776" _null_ _null_ _null_ _null_ _null_ array_agg_transfn _null_ _null_ _null_ ));
 DESCR("aggregate transition function");
+DATA(insert OID = 3423 (  array_agg_combine	 PGNSP PGUID 12 1 0 0 0 f f f f f i s 2 0 2281 "2281 2281" _null_ _null_ _null_ _null_ _null_ array_agg_combine _null_ _null_ _null_ ));
+DESCR("aggregate combine function");
+DATA(insert OID = 3424 (  array_agg_serialize    PGNSP PGUID 12 1 0 0 0 f f f t f i s 1 0 17 "2281" _null_ _null_ _null_ _null_ _null_ array_agg_serialize _null_ _null_ _null_ ));
+DESCR("aggregate serial function");
+DATA(insert OID = 3425 (  array_agg_deserialize	 PGNSP PGUID 12 1 0 0 0 f f f t f i s 2 0 2281 "17 2281" _null_ _null_ _null_ _null_ _null_ array_agg_deserialize _null_ _null_ _null_ ));
+DESCR("aggregate deserial function");
 DATA(insert OID = 2334 (  array_agg_finalfn   PGNSP PGUID 12 1 0 0 0 f f f f f i s 2 0 2277 "2281 2776" _null_ _null_ _null_ _null_ _null_ array_agg_finalfn _null_ _null_ _null_ ));
 DESCR("aggregate final function");
 DATA(insert OID = 2335 (  array_agg		   PGNSP PGUID 12 1 0 0 0 a f f f f i s 1 0 2277 "2776" _null_ _null_ _null_ _null_ _null_ aggregate_dummy _null_ _null_ _null_ ));
 DESCR("concatenate aggregate input into an array");
 DATA(insert OID = 4051 (  array_agg_array_transfn	PGNSP PGUID 12 1 0 0 0 f f f f f i s 2 0 2281 "2281 2277" _null_ _null_ _null_ _null_ _null_ array_agg_array_transfn _null_ _null_ _null_ ));
 DESCR("aggregate transition function");
+DATA(insert OID = 3426 (  array_agg_array_combine	 PGNSP PGUID 12 1 0 0 0 f f f f f i s 2 0 2281 "2281 2281" _null_ _null_ _null_ _null_ _null_ array_agg_array_combine _null_ _null_ _null_ ));
+DESCR("aggregate combine function");
+DATA(insert OID = 3427 (  array_agg_array_serialize    PGNSP PGUID 12 1 0 0 0 f f f t f i s 1 0 17 "2281" _null_ _null_ _null_ _null_ _null_ array_agg_array_serialize _null_ _null_ _null_ ));
+DESCR("aggregate serial function");
+DATA(insert OID = 3428 (  array_agg_array_deserialize	 PGNSP PGUID 12 1 0 0 0 f f f t f i s 2 0 2281 "17 2281" _null_ _null_ _null_ _null_ _null_ array_agg_array_deserialize _null_ _null_ _null_ ));
+DESCR("aggregate deserial function");
 DATA(insert OID = 4052 (  array_agg_array_finalfn	PGNSP PGUID 12 1 0 0 0 f f f f f i s 2 0 2277 "2281 2277" _null_ _null_ _null_ _null_ _null_ array_agg_array_finalfn _null_ _null_ _null_ ));
 DESCR("aggregate final function");
 DATA(insert OID = 4053 (  array_agg		   PGNSP PGUID 12 1 0 0 0 a f f f f i s 1 0 2277 "2277" _null_ _null_ _null_ _null_ _null_ aggregate_dummy _null_ _null_ _null_ ));
@@ -2710,12 +2722,23 @@ DESCR("aggregate final function");
 
 DATA(insert OID = 3535 (  string_agg_transfn		PGNSP PGUID 12 1 0 0 0 f f f f f i s 3 0 2281 "2281 25 25" _null_ _null_ _null_ _null_ _null_ string_agg_transfn _null_ _null_ _null_ ));
 DESCR("aggregate transition function");
+DATA(insert OID = 3429 (  string_agg_combine		PGNSP PGUID 12 1 0 0 0 f f f f f i s 2 0 2281 "2281 2281" _null_ _null_ _null_ _null_ _null_ string_agg_combine _null_ _null_ _null_ ));
+DESCR("aggregate combine function");
+DATA(insert OID = 3430 (  string_agg_serialize		PGNSP PGUID 12 1 0 0 0 f f f t f i s 1 0 17 "2281" _null_ _null_ _null_ _null_ _null_ string_agg_serialize _null_ _null_ _null_ ));
+DESCR("aggregate serial function");
+DATA(insert OID = 3431 (  string_agg_deserialize	PGNSP PGUID 12 1 0 0 0 f f f t f i s 2 0 2281 "17 2281" _null_ _null_ _null_ _null_ _null_ string_agg_deserialize _null_ _null_ _null_ ));
+DESCR("aggregate deserial function");
+
 DATA(insert OID = 3536 (  string_agg_finalfn		PGNSP PGUID 12 1 0 0 0 f f f f f i s 1 0 25 "2281" _null_ _null_ _null_ _null_ _null_ string_agg_finalfn _null_ _null_ _null_ ));
 DESCR("aggregate final function");
 DATA(insert OID = 3538 (  string_agg				PGNSP PGUID 12 1 0 0 0 a f f f f i s 2 0 25 "25 25" _null_ _null_ _null_ _null_ _null_ aggregate_dummy _null_ _null_ _null_ ));
 DESCR("concatenate aggregate input into a string");
 DATA(insert OID = 3543 (  bytea_string_agg_transfn	PGNSP PGUID 12 1 0 0 0 f f f f f i s 3 0 2281 "2281 17 17" _null_ _null_ _null_ _null_ _null_ bytea_string_agg_transfn _null_ _null_ _null_ ));
 DESCR("aggregate transition function");
+DATA(insert OID = 3432 (  bytea_string_agg_serialize		PGNSP PGUID 12 1 0 0 0 f f f t f i s 1 0 17 "2281" _null_ _null_ _null_ _null_ _null_ bytea_string_agg_serialize _null_ _null_ _null_ ));
+DESCR("aggregate serial function");
+DATA(insert OID = 3433 (  bytea_string_agg_deserialize	PGNSP PGUID 12 1 0 0 0 f f f t f i s 2 0 2281 "17 2281" _null_ _null_ _null_ _null_ _null_ bytea_string_agg_deserialize _null_ _null_ _null_ ));
+DESCR("aggregate deserial function");
 DATA(insert OID = 3544 (  bytea_string_agg_finalfn	PGNSP PGUID 12 1 0 0 0 f f f f f i s 1 0 17 "2281" _null_ _null_ _null_ _null_ _null_ bytea_string_agg_finalfn _null_ _null_ _null_ ));
 DESCR("aggregate final function");
 DATA(insert OID = 3545 (  string_agg				PGNSP PGUID 12 1 0 0 0 a f f f f i s 2 0 17 "17 17" _null_ _null_ _null_ _null_ _null_ aggregate_dummy _null_ _null_ _null_ ));
diff --git a/src/include/utils/array.h b/src/include/utils/array.h
index afbb532e9c2..f99e05a2584 100644
--- a/src/include/utils/array.h
+++ b/src/include/utils/array.h
@@ -393,6 +393,9 @@ extern bool array_contains_nulls(ArrayType *array);
 
 extern ArrayBuildState *initArrayResult(Oid element_type,
 				MemoryContext rcontext, bool subcontext);
+extern ArrayBuildState *initArrayResultWithSize(Oid element_type,
+						MemoryContext rcontext,
+						bool subcontext, int initsize);
 extern ArrayBuildState *accumArrayResult(ArrayBuildState *astate,
 				 Datum dvalue, bool disnull,
 				 Oid element_type,