Reduce memory usage when indexing Hypercore TAM

When building indexes over a table using Hypercore TAM, some memory
for decompressing data wasn't released until the index build
completes. This change optimizes the memory usage during index builds
to release memory after every compressed batch has been processed.

tsl/src/hypercore/hypercore_handler.c

@@ -2790,6 +2790,7 @@ typedef struct IndexBuildCallbackState
 	Bitmapset *orderby_cols;
 	bool is_segmentby_index;
 	MemoryContext decompression_mcxt;
+	MemoryContext batch_mcxt;
 	ArrowArray **arrow_columns;
 } IndexBuildCallbackState;
 
@@ -2829,6 +2830,9 @@ hypercore_index_build_callback(Relation index, ItemPointer tid, Datum *values, b
 									   * the actual number of rows to indexing
 									   * only one row per segment. */
 
+	MemoryContext old_mcxt = MemoryContextSwitchTo(icstate->batch_mcxt);
+	MemoryContextReset(icstate->batch_mcxt);
+
 	/* Update ntuples for accurate statistics. When building the index, the
 	 * relation's reltuples is updated based on this count. */
 	if (tupleIsAlive)
@@ -2878,7 +2882,7 @@ hypercore_index_build_callback(Relation index, ItemPointer tid, Datum *values, b
 					TupleDescAttr(tupdesc, AttrNumberGetAttrOffset(attno));
 				icstate->arrow_columns[i] = arrow_from_compressed(values[i],
 																  attr->atttypid,
-																  CurrentMemoryContext,
+																  icstate->batch_mcxt,
 																  icstate->decompression_mcxt);
 
 				/* The number of elements in the arrow array should be the
@@ -2911,7 +2915,7 @@ hypercore_index_build_callback(Relation index, ItemPointer tid, Datum *values, b
 		/* The slot is a table slot, not index slot. But we only fill in the
 		 * columns needed for the index and predicate checks. Therefore, make sure
 		 * other columns are initialized to "null" */
-		memset(slot->tts_isnull, true, sizeof(bool) * slot->tts_tupleDescriptor->natts);
+		MemSet(slot->tts_isnull, true, sizeof(bool) * slot->tts_tupleDescriptor->natts);
 		ExecClearTuple(slot);
 
 		for (int colnum = 0; colnum < natts; colnum++)
@@ -2950,6 +2954,9 @@ hypercore_index_build_callback(Relation index, ItemPointer tid, Datum *values, b
 		hypercore_tid_encode(&index_tid, tid, rownum + 1);
 		Assert(!icstate->is_segmentby_index || rownum == 0);
 
+		/* Reset memory for predicate checks */
+		MemoryContextReset(icstate->econtext->ecxt_per_tuple_memory);
+
 		/*
 		 * In a partial index, discard tuples that don't satisfy the
 		 * predicate.
@@ -2963,8 +2970,13 @@ hypercore_index_build_callback(Relation index, ItemPointer tid, Datum *values, b
 				continue;
 		}
 
+		/* Call the original callback on the original memory context */
+		MemoryContextSwitchTo(old_mcxt);
 		icstate->callback(index, &index_tid, values, isnull, tupleIsAlive, icstate->orig_state);
+		MemoryContextSwitchTo(icstate->batch_mcxt);
 	}
+
+	MemoryContextSwitchTo(old_mcxt);
 }
 
 /*
@@ -3125,8 +3137,11 @@ hypercore_index_build_range_scan(Relation relation, Relation indexRelation, Inde
 		.index_info = indexInfo,
 		.tuple_index = -1,
 		.ntuples = 0,
+		.batch_mcxt = AllocSetContextCreate(CurrentMemoryContext,
+											"Compressed batch for index build",
+											ALLOCSET_DEFAULT_SIZES),
 		.decompression_mcxt = AllocSetContextCreate(CurrentMemoryContext,
-													"bulk decompression",
+													"Bulk decompression for index build",
 													/* minContextSize = */ 0,
 													/* initBlockSize = */ 64 * 1024,
 													/* maxBlockSize = */ 64 * 1024),
@@ -3265,6 +3280,7 @@ hypercore_index_build_range_scan(Relation relation, Relation indexRelation, Inde
 	FreeExecutorState(icstate.estate);
 	ExecDropSingleTupleTableSlot(icstate.slot);
 	MemoryContextDelete(icstate.decompression_mcxt);
+	MemoryContextDelete(icstate.batch_mcxt);
 	pfree((void *) icstate.arrow_columns);
 	bms_free(icstate.segmentby_cols);
 	bms_free(icstate.orderby_cols);