chimera:optimise db call

Motivation

as it has been suggested in review for the patch https://rb.dcache.org/r/13421/,
using  WHERE NOT EXISTS will use fewer DB round-trips and it doesn't force strong transactional isolation.

Target: master
Acked-by: Tigran Mkrtchyan
Requires-notes: no
Requires-book: no

modules/chimera/src/main/java/org/dcache/chimera/FsSqlDriver.java

@@ -2044,14 +2044,14 @@ void addLabel(FsInode inode, String labelname) throws ChimeraFsException {
                       }, keyHolder);
                 Long label_id = (Long) keyHolder.getKeys().get("label_id");
 
-                //TODO change to WHERE NOT EXISTS
                 _jdbc.update("INSERT INTO t_labels_ref (label_id, inumber) VALUES (?,?)",
                       label_id, inode.ino());
 
             } else {
 
                 Long label_id = getLabel(labelname);
 
+
                 Integer n = _jdbc.queryForObject(
                       "SELECT count(*) FROM t_labels_ref WHERE inumber=? and label_id = ?",
                       Integer.class, inode.ino(), label_id);
@@ -2060,6 +2060,21 @@ void addLabel(FsInode inode, String labelname) throws ChimeraFsException {
                     _jdbc.update("INSERT INTO t_labels_ref (label_id, inumber) VALUES (?,?)",
                           label_id, inode.ino());
                 }
+
+                _jdbc.update(
+                      "INSERT INTO t_labels_ref (label_id, inumber) (SELECT * FROM (VALUES (?,?)) v  WHERE NOT EXISTS "
+                            +
+                            "(SELECT label_id FROM t_labels_ref WHERE label_id = ?  and inumber=?))",
+                      ps -> {
+                          ps.setLong(1, label_id);
+                          ps.setLong(2, inode.ino());
+                          ps.setLong(3, label_id);
+                          ps.setLong(4, inode.ino());
+
+                      });
+
+
+
             }
 
         } catch (EmptyResultDataAccessException e) {

modules/chimera/src/main/java/org/dcache/chimera/PgSQL95FsSqlDriver.java

@@ -19,7 +19,9 @@
 import com.google.common.base.Throwables;
 import java.io.File;
 import java.net.SocketException;
+import java.sql.PreparedStatement;
 import java.sql.ResultSet;
+import java.sql.Statement;
 import java.sql.Timestamp;
 import java.util.ArrayList;
 import java.util.Collections;
@@ -34,7 +36,10 @@
 import org.slf4j.LoggerFactory;
 import org.springframework.dao.DataAccessException;
 import org.springframework.dao.DuplicateKeyException;
+import org.springframework.dao.EmptyResultDataAccessException;
 import org.springframework.dao.IncorrectUpdateSemanticsDataAccessException;
+import org.springframework.jdbc.support.GeneratedKeyHolder;
+import org.springframework.jdbc.support.KeyHolder;
 
 /**
  * PostgreSQL 9.5 and later specific
@@ -312,6 +317,61 @@ void addInodeLocation(FsInode inode, int type, String location) {
               });
     }
 
+
+    /**
+     * Attache a given label to  a given file system object.
+     *
+     * @param inode     file system object.
+     * @param labelname label name.
+     * @throws ChimeraFsException
+     */
+    void addLabel(FsInode inode, String labelname) throws ChimeraFsException {
+
+        KeyHolder keyHolder = new GeneratedKeyHolder();
+        try {
+
+            int n = _jdbc.update(
+                  con -> {
+                      PreparedStatement ps = con.prepareStatement(
+                            "INSERT INTO t_labels ( labelname) VALUES (?)"
+                                  + "ON CONFLICT ON CONSTRAINT labelname DO NOTHING",
+                            Statement.RETURN_GENERATED_KEYS);
+                      ps.setString(1, labelname);
+
+                      return ps;
+                  }, keyHolder);
+            if (n != 0) {
+                Long label_id = (Long) keyHolder.getKeys().get("label_id");
+
+                _jdbc.update("INSERT INTO t_labels_ref (label_id, inumber) VALUES (?,?)",
+                      label_id, inode.ino());
+
+            } else {
+
+
+                Long label_id = getLabel(labelname);
+
+                _jdbc.update(
+                      "INSERT INTO t_labels_ref (label_id, inumber) (SELECT * FROM (VALUES (?,?)) "
+                            + "ON CONFLICT ON CONSTRAINT i_label_pkey DO NOTHING",
+
+                      ps -> {
+                          ps.setLong(1, label_id);
+                          ps.setLong(2, inode.ino());
+                          ps.setLong(3, label_id);
+                          ps.setLong(4, inode.ino());
+
+                      });
+
+
+            }
+
+        } catch (EmptyResultDataAccessException e) {
+            throw new NoLabelChimeraException(labelname);
+        }
+
+    }
+
     @Override
     void copyTags(FsInode orign, FsInode destination) {
         _jdbc.queryForList(