From f8eb0537e2ce89ddec9327a6942540332b61ce6b Mon Sep 17 00:00:00 2001
From: Nils Dijk <nils@citusdata.com>
Date: Fri, 18 Jun 2021 16:32:13 +0200
Subject: [PATCH] apply visibility during reads

---
 src/backend/columnar/columnar_metadata.c | 38 ++++++++++++++++++++++++
 src/backend/columnar/columnar_reader.c   | 12 ++++++++
 src/include/columnar/columnar.h          |  2 ++
 3 files changed, 52 insertions(+)

diff --git a/src/backend/columnar/columnar_metadata.c b/src/backend/columnar/columnar_metadata.c
index e1cab2f19..8833943af 100644
--- a/src/backend/columnar/columnar_metadata.c
+++ b/src/backend/columnar/columnar_metadata.c
@@ -1367,6 +1367,44 @@ ColumnarVisibilityRelationId(void)
 }
 
 
+Bitmapset *
+ReadDeletedTuplesForStripe(RelFileNode relfilenode, uint64 stripenum, Snapshot snapshot)
+{
+	Bitmapset *deletedTuples = NULL;
+
+	uint64 storageId = LookupStorageId(relfilenode);
+	ScanKeyData scanKey[2];
+	ScanKeyInit(&scanKey[0], Anum_columnar_visibility_storage_id,
+				BTEqualStrategyNumber, F_OIDEQ, UInt64GetDatum(storageId));
+	ScanKeyInit(&scanKey[1], Anum_columnar_visibility_stripe_num,
+				BTEqualStrategyNumber, F_OIDEQ, UInt64GetDatum(stripenum));
+
+	Relation columnarVisibility = table_open(ColumnarVisibilityRelationId(),
+											 AccessShareLock);
+	Relation index = index_open(ColumnarVisibilityIndexRelationId(), AccessShareLock);
+	SysScanDesc scanDescriptor = systable_beginscan_ordered(columnarVisibility, index,
+															snapshot, 2, scanKey);
+	HeapTuple heapTuple = NULL;
+	while (HeapTupleIsValid(heapTuple = systable_getnext(scanDescriptor)))
+	{
+		TupleDesc tupleDescriptor = RelationGetDescr(columnarVisibility);
+		Datum datumArray[Natts_columnar_visibility];
+		bool isNullArray[Natts_columnar_visibility];
+		heap_deform_tuple(heapTuple, tupleDescriptor, datumArray, isNullArray);
+
+		uint64 rownum = DatumGetUInt64(datumArray[Anum_columnar_visibility_row_num - 1]);
+
+		deletedTuples = bms_add_member(deletedTuples, (int) rownum);
+	}
+
+	systable_endscan_ordered(scanDescriptor);
+	index_close(index, AccessShareLock);
+	table_close(columnarVisibility, AccessShareLock);
+
+	return deletedTuples;
+}
+
+
 /*
  * ColumnarVisibilityIndexRelationId returns relation id of columnar.visibility_pkey.
  */
diff --git a/src/backend/columnar/columnar_reader.c b/src/backend/columnar/columnar_reader.c
index 0fc3e370d..77e17cd94 100644
--- a/src/backend/columnar/columnar_reader.c
+++ b/src/backend/columnar/columnar_reader.c
@@ -60,6 +60,8 @@ typedef struct StripeReadState
 	StripeBuffers *stripeBuffers;   /* allocated in stripeReadContext */
 	List *projectedColumnList;      /* borrowed reference */
 	ChunkGroupReadState *chunkGroupReadState; /* owned */
+
+	Bitmapset *deletedTuples;
 } StripeReadState;
 
 struct ColumnarReadState
@@ -428,6 +430,9 @@ BeginStripeRead(StripeMetadata *stripeMetadata, Relation rel, TupleDesc tupleDes
 
 	stripeReadState->rowCount = stripeReadState->stripeBuffers->rowCount;
 
+	stripeReadState->deletedTuples = ReadDeletedTuplesForStripe(rel->rd_node,
+																stripeMetadata->id, NULL);
+
 	MemoryContextSwitchTo(oldContext);
 
 
@@ -506,6 +511,13 @@ ReadStripeNextRow(StripeReadState *stripeReadState, Datum *columnValues,
 			continue;
 		}
 
+		/* check if tuple has been removed earlier, read next if that has happened */
+		if (bms_is_member(stripeReadState->currentRow, stripeReadState->deletedTuples))
+		{
+			stripeReadState->currentRow++;
+			continue;
+		}
+
 		stripeReadState->currentRow++;
 		return true;
 	}
diff --git a/src/include/columnar/columnar.h b/src/include/columnar/columnar.h
index cef822e1b..5c1618489 100644
--- a/src/include/columnar/columnar.h
+++ b/src/include/columnar/columnar.h
@@ -262,6 +262,8 @@ extern StripeMetadata * FindStripeByRowNumber(RelFileNode relfilenode, uint64 ro
 											  Snapshot snapshot);
 extern StripeMetadata * FindStripeWithHighestRowNumber(Relation relation,
 													   Snapshot snapshot);
+extern Bitmapset * ReadDeletedTuplesForStripe(RelFileNode relfilenode, uint64 stripenum,
+											  Snapshot snapshot);
 extern Datum columnar_relation_storageid(PG_FUNCTION_ARGS);