[Enhancement]tune default virtual node to be more friendly to cache (#38270)

Signed-off-by: zombee0 <[email protected]>

Author: zombee0

fe/fe-core/src/main/java/com/starrocks/qe/HDFSBackendSelector.java

@@ -86,7 +86,7 @@ public class HDFSBackendSelector implements BackendSelector {
     // After testing, this value can ensure that the scan range size assigned to each BE is as uniform as possible,
     // and the largest scan data is not more than 1.1 times of the average value
     private final double kMaxImbalanceRatio = 1.1;
-    public static final int CONSISTENT_HASH_RING_VIRTUAL_NUMBER = 128;
+    public static final int CONSISTENT_HASH_RING_VIRTUAL_NUMBER = 256;
 
     class HdfsScanRangeHasher {
         String basePath;

fe/fe-core/src/main/java/com/starrocks/qe/SessionVariable.java

@@ -1226,7 +1226,7 @@ public static MaterializedViewRewriteMode parse(String str) {
     private String hdfsBackendSelectorHashAlgorithm = "consistent";
 
     @VariableMgr.VarAttr(name = CONSISTENT_HASH_VIRTUAL_NUMBER, flag = VariableMgr.INVISIBLE)
-    private int consistentHashVirtualNodeNum = 128;
+    private int consistentHashVirtualNodeNum = 256;
 
     // binary, json, compact,
     @VarAttr(name = THRIFT_PLAN_PROTOCOL)