Prevent from DB lock waits on concurrent use of .bvfs_update

Until this change, the HasCache column in the Job table was either 0 or
1, where 0 represents the state bvfs cache does not exist and 1
represents bvfs cache exists. This change introduces -1 representing the
state bvfs cache update in progress. Before starting the bvfs cache
update, it is now checked if HasCache is -1, in that case the
.bvfs_update jobid=n command will return an ERROR: BVFS reported a
problem for 107. This change also prevents from duplicate key violations
that could occur before on the PathHierarchy table.

src/cats/bvfs.c

@@ -248,9 +248,19 @@ static void build_path_hierarchy(JCR *jcr, B_DB *mdb,
             }
             ppathid_cache.insert(pathid);
 
+            /* Prevent from ERROR:  duplicate key value violates unique
+             * constraint "pathhierarchy_pkey" when multiple .bvfs_update
+             * to prevent from unique key violation when multiple .bvfs_update
+             * are run parallel.
+             * The syntax of the following quere works for PostgreSQL, MySQL
+             * and SQLite
+             */
             Mmsg(mdb->cmd,
-                 "INSERT INTO PathHierarchy (PathId, PPathId) "
-                 "VALUES (%s,%lld)",
+                 "INSERT INTO PathHierarchy (PathId,PPathId) "
+                    "SELECT ph.PathId,ph.PPathId FROM "
+                       "(SELECT %s AS PathId, %lld AS PPathId) ph "
+                       "WHERE NOT EXISTS "
+                       "(SELECT 1 FROM PathHierarchy phi WHERE phi.PathId = ph.PathId)",
                  pathid, (uint64_t) parent.PathId);
 
             if (!INSERT_DB(jcr, mdb, mdb->cmd)) {
@@ -300,6 +310,23 @@ static bool update_path_hierarchy_cache(JCR *jcr,
       goto bail_out;
    }
 
+   /* prevent from DB lock waits when already in progress */
+   Mmsg(mdb->cmd, "SELECT 1 FROM Job WHERE JobId = %s AND HasCache=-1", jobid);
+
+   if (!QUERY_DB(jcr, mdb, mdb->cmd) || sql_num_rows(mdb) > 0) {
+      Dmsg1(dbglevel, "already in progress %d\n", (uint32_t)JobId );
+      retval = false;
+      goto bail_out;
+   }
+
+   /* set HasCache to -1 in Job (in progress) */
+   Mmsg(mdb->cmd, "UPDATE Job SET HasCache=-1 WHERE JobId=%s", jobid);
+   UPDATE_DB(jcr, mdb, mdb->cmd);
+
+   /* need to COMMIT here and start a new transaction */
+   db_end_transaction(jcr, mdb);
+   db_start_transaction(jcr, mdb);
+
    /* Inserting path records for JobId */
    Mmsg(mdb->cmd, "INSERT INTO PathVisibility (PathId, JobId) "
                    "SELECT DISTINCT PathId, JobId "
@@ -450,7 +477,7 @@ bool bvfs_update_path_hierarchy_cache(JCR *jcr, B_DB *mdb, char *jobids)
    char *p;
    int status;
    JobId_t JobId;
-   bool retval = false;
+   bool retval = true;
    pathid_cache ppathid_cache;
 
    p = jobids;
@@ -464,13 +491,12 @@ bool bvfs_update_path_hierarchy_cache(JCR *jcr, B_DB *mdb, char *jobids)
          /*
           * We reached the end of the list.
           */
-         retval = true;
          goto bail_out;
       }
 
       Dmsg1(dbglevel, "Updating cache for %lld\n", (uint64_t)JobId);
       if (!update_path_hierarchy_cache(jcr, mdb, ppathid_cache, JobId)) {
-         goto bail_out;
+         retval = false;
       }
    }