job-list: read from sqlite if necessary

Problem: Now that inactive jobs are stored to an sqlite database,
it is possible to retrieve additional job information that is no
longer stored in memory.

Solution: When possible, read from sqlite to get additional job
information about inactive jobs.

src/modules/job-list/job_data.c

@@ -38,10 +38,12 @@ void job_destroy (void *data)
         hostlist_destroy (job->nodelist_hl);
         json_decref (job->annotations);
         grudgeset_destroy (job->dependencies);
+        json_decref (job->dependencies_db);
         json_decref (job->jobspec);
         json_decref (job->R);
         free (job->eventlog);
         json_decref (job->exception_context);
+        json_decref (job->job_dbdata);
         free (job);
         errno = save_errno;
     }

src/modules/job-list/job_data.h

@@ -65,7 +65,11 @@ struct job {
     const char *exception_note;
     flux_job_result_t result;
     json_t *annotations;
+    /* dependencies - built up
+     * dependencies_db - recovered from db
+     */
     struct grudgeset *dependencies;
+    json_t *dependencies_db;
 
     /* cache of job information */
     json_t *jobspec;
@@ -74,6 +78,9 @@ struct job {
     size_t eventlog_len;
     json_t *exception_context;
 
+    /* all job data from db */
+    json_t *job_dbdata;
+
     /* Track which states we have seen and have completed transition
      * to.  States we've processed via the states_mask and states seen
      * via events stream in states_events_mask.

src/modules/job-list/job_util.c

@@ -205,7 +205,10 @@ static int store_attr (struct job *job,
     else if (streq (attr, "dependencies")) {
         if (!job->dependencies)
             return 0;
-        val = json_incref (grudgeset_tojson (job->dependencies));
+        if (job->dependencies_db)
+            val = json_incref (job->dependencies_db);
+        else
+            val = json_incref (grudgeset_tojson (job->dependencies));
     }
     else {
         errprintf (errp, "%s is not a valid attribute", attr);