deniskuzZ commented on a change in pull request #2266:
URL: https://github.com/apache/hive/pull/2266#discussion_r636228265



##########
File path: 
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/txn/TxnHandler.java
##########
@@ -5390,6 +5406,493 @@ public void countOpenTxns() throws MetaException {
     }
   }
 
+  private void cleanOldStatsFromPartColStatTable(Map<String, PartitionInfo> 
statsPartInfoMap,
+                                                 Map<String, ColumnStatistics> 
newStatsMap,
+                                                 Connection dbConn) throws 
SQLException {
+    PreparedStatement statementDelete = null;
+    int numRows = 0;
+    int maxNumRows = MetastoreConf.getIntVar(conf, 
ConfVars.DIRECT_SQL_MAX_ELEMENTS_VALUES_CLAUSE);
+    String delete = "DELETE FROM \"PART_COL_STATS\" where \"PART_ID\" = ? AND 
\"COLUMN_NAME\" = ?";
+
+    try {
+      statementDelete = dbConn.prepareStatement(delete);
+      for (Map.Entry entry : newStatsMap.entrySet()) {
+        // If the partition does not exist (deleted/removed by some other 
task), no need to update the stats.
+        if (!statsPartInfoMap.containsKey(entry.getKey())) {
+          continue;
+        }
+
+        ColumnStatistics colStats = (ColumnStatistics) entry.getValue();
+        for (ColumnStatisticsObj statisticsObj : colStats.getStatsObj()) {
+          statementDelete.setLong(1, 
statsPartInfoMap.get(entry.getKey()).partitionId);
+          statementDelete.setString(2, statisticsObj.getColName());
+          numRows++;
+          statementDelete.addBatch();
+          if (numRows == maxNumRows) {
+            statementDelete.executeBatch();
+            numRows = 0;
+            LOG.info("Executed delete " + delete + " for numRows " + numRows);
+          }
+        }
+      }
+
+      if (numRows != 0) {
+        statementDelete.executeBatch();
+      }
+    } finally {
+      closeStmt(statementDelete);
+    }
+  }
+
+  private long getMaxCSId(Connection dbConn) throws SQLException {
+    Statement stmtInt = null;
+    ResultSet rsInt = null;
+    long maxCsId = 0;
+    try {
+      stmtInt = dbConn.createStatement();
+      while (maxCsId == 0) {
+        String query = "SELECT \"NEXT_VAL\" FROM \"SEQUENCE_TABLE\" WHERE 
\"SEQUENCE_NAME\"= "

Review comment:
       that would create lock on SEQUENCE_TABLE for the duration of the whole 
stats update operation. Won't it interfere with the regular flow? 
   




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