DBPE-14965: Don't mix indexing static and non-static rows

An index on static column indexes static rows only,
an index on non-static column indexes regular rows only.

Because the partition key is always present in static rows,
before this patch,
an index on partition key received both static and non-static
rows which could lead to duplicates under some circumstances.

src/java/org/apache/cassandra/index/sai/disk/v1/SSTableIndexWriter.java

@@ -105,6 +105,12 @@ public void addRow(PrimaryKey key, Row row, long sstableRowId) throws IOExceptio
         if (maybeAbort())
             return;
 
+        // This is to avoid duplicates (and also reduce space taken by indexes on static columns).
+        // An index on a static column indexes static rows only.
+        // An index on a non-static column indexes regular rows only.
+        if (indexContext.getDefinition().isStatic() != row.isStatic())
+            return;
+
         if (indexContext.isNonFrozenCollection())
         {
             Iterator<ByteBuffer> valueIterator = indexContext.getValuesOf(row, nowInSec);

test/unit/org/apache/cassandra/index/sai/cql/DBPE14965Test.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright DataStax, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.cassandra.index.sai.cql;
+
+import org.junit.Test;
+
+import org.apache.cassandra.index.sai.SAITester;
+import org.assertj.core.api.Assertions;
+
+public class DBPE14965Test extends SAITester
+{
+    @Test
+    public void testDBPE14965()
+    {
+        createTable("CREATE TABLE %s (" +
+                    "    pk1 int," +
+                    "    pk2 int," +
+                    "    ck int," +
+                    "    r int," +
+                    "    s int static," +
+                    "    PRIMARY KEY ((pk1, pk2), ck))");
+
+        createIndex("CREATE CUSTOM INDEX ON %s (pk1) USING 'StorageAttachedIndex'");
+
+        disableCompaction();
+        execute("INSERT INTO %s (pk1, pk2, ck, r, s) VALUES (0, ?, ?, ?, ?)", 1, 1, 1, 1);
+        flush();
+        compact();
+
+        Assertions.assertThat(execute("SELECT * FROM %s WHERE pk1=0").size()).isEqualTo(1); // finds 2!!
+    }
+}