This is an automated cherry-pick of pingcap#2740

Signed-off-by: ti-chi-bot <ti-community-prow-bot@tidb.io>

Author: shiyuhang0

core/src/test/scala/org/apache/spark/sql/IssueTestSuite.scala

@@ -21,6 +21,47 @@ import org.apache.spark.sql.functions.{col, sum}
 
 class IssueTestSuite extends BaseTiSparkTest {
 
+<<<<<<< HEAD
+=======
+  test("test tiflash overflow in unsigned bigint") {
+    if (!enableTiFlashTest) {
+      cancel("tiflash test not enabled")
+    }
+    val dbTable = "tispark_test.tiflash_overflow"
+    tidbStmt.execute(s"drop table if exists $dbTable")
+    tidbStmt.execute(
+      s"CREATE TABLE $dbTable (`a` bigint(20) UNSIGNED NOT NULL,`b` bigint(20) UNSIGNED NOT NULL)")
+    tidbStmt.execute(s"insert into $dbTable values(16717361816800086255, 16717361816800086255)")
+    tidbStmt.execute(s"ALTER TABLE $dbTable SET TIFLASH REPLICA 1")
+
+    Thread.sleep(5 * 1000)
+
+    val prev = spark.conf.getOption(TiConfigConst.ISOLATION_READ_ENGINES)
+    try {
+      spark.conf
+        .set(TiConfigConst.ISOLATION_READ_ENGINES, TiConfigConst.TIFLASH_STORAGE_ENGINE)
+      val df = spark.sql(s"select * from $dbTable")
+      val row = Row(BigDecimal("16717361816800086255"), BigDecimal("16717361816800086255"))
+      checkAnswer(df, Seq(row))
+    } finally {
+      spark.conf.set(
+        TiConfigConst.ISOLATION_READ_ENGINES,
+        prev.getOrElse(TiConfigConst.DEFAULT_STORAGE_ENGINES))
+    }
+  }
+
+  test("test issue 2649") {
+    val dbTable = "tispark_test.mutil_uniq"
+    tidbStmt.execute(s"drop table if exists $dbTable")
+    tidbStmt.execute(
+      s"CREATE TABLE $dbTable (`a` int(5) NOT NULL,`b` int(5) NOT NULL,UNIQUE KEY `idx_ab` (`a`,`b`))")
+    tidbStmt.execute(s"insert into $dbTable values(0, 0),(1,1)")
+    val df = spark.sql(s"select * from $dbTable where a=1")
+    val row1 = Row(1, 1)
+    checkAnswer(df, Seq(row1))
+  }
+
+>>>>>>> 044630939 (Fix TiFlash overflow (#2740))
   //https://github.com/pingcap/tispark/issues/2268
   test("show rowid in commonhandle") {
     spark.sqlContext.setConf(TiConfigConst.SHOW_ROWID, "true")

tikv-client/src/main/java/com/pingcap/tikv/columnar/TiBlockColumnVector.java

@@ -17,13 +17,18 @@
 
 import static com.pingcap.tikv.util.MemoryUtil.EMPTY_BYTE_BUFFER_DIRECT;
 
+<<<<<<< HEAD
 import com.pingcap.tikv.ExtendedDateTime;
+=======
+import com.google.common.primitives.UnsignedLong;
+>>>>>>> 044630939 (Fix TiFlash overflow (#2740))
 import com.pingcap.tikv.codec.Codec.DateCodec;
 import com.pingcap.tikv.codec.Codec.DateTimeCodec;
 import com.pingcap.tikv.columnar.datatypes.CHType;
 import com.pingcap.tikv.types.AbstractDateTimeType;
 import com.pingcap.tikv.types.BytesType;
 import com.pingcap.tikv.types.DateType;
+import com.pingcap.tikv.types.DecimalType;
 import com.pingcap.tikv.util.MemoryUtil;
 import java.math.BigDecimal;
 import java.nio.ByteBuffer;
@@ -236,6 +241,10 @@ public double getDouble(int rowId) {
   @Override
   public BigDecimal getDecimal(int rowId, int precision, int scale) {
     long rowIdAddr = (long) rowId * fixedLength + dataAddr;
+    // avoid unsigned long overflow here
+    if (type == DecimalType.BIG_INT_DECIMAL) {
+      return new BigDecimal(UnsignedLong.fromLongBits(this.getLong(rowId)).bigIntegerValue());
+    }
     if (fixedLength == 4) {
       return MemoryUtil.getDecimal32(rowIdAddr, scale);
     } else if (fixedLength == 8) {