Get update every from page (#14573)

* Fix warning on conversion unsigned vs int

* For each metric get the update every from the last page stored in the journal

database/engine/datafile.c

@@ -379,8 +379,8 @@ static int scan_data_files_cmp(const void *a, const void *b)
 /* Returns number of datafiles that were loaded or < 0 on error */
 static int scan_data_files(struct rrdengine_instance *ctx)
 {
-    int ret;
-    unsigned tier, no, matched_files, i,failed_to_load;
+    int ret, matched_files, failed_to_load;
+    unsigned tier, no, i;
     uv_fs_t req;
     uv_dirent_t dent;
     struct rrdengine_datafile **datafiles, *datafile;

database/engine/journalfile.c

@@ -894,6 +894,16 @@ static int journalfile_v2_validate(void *data_start, size_t journal_v2_file_size
     return 0;
 }
 
+static inline time_t get_metric_latest_update_every(struct journal_page_header *metric_list_header)
+{
+    struct journal_page_list *metric_page =
+        (struct journal_page_list *)((uint8_t *)metric_list_header + sizeof(*metric_list_header));
+    uint32_t entries = metric_list_header->entries;
+    if (unlikely(!entries))
+        return 0;
+    return (time_t)metric_page[entries - 1].update_every_s;
+}
+
 void journalfile_v2_populate_retention_to_mrg(struct rrdengine_instance *ctx, struct rrdengine_journalfile *journalfile) {
     usec_t started_ut = now_monotonic_usec();
 
@@ -911,7 +921,7 @@ void journalfile_v2_populate_retention_to_mrg(struct rrdengine_instance *ctx, st
     for (size_t i=0; i < entries; i++) {
         time_t start_time_s = header_start_time_s + metric->delta_start_s;
         time_t end_time_s = header_start_time_s + metric->delta_end_s;
-        time_t update_every_s = (metric->entries > 1) ? ((end_time_s - start_time_s) / (entries - 1)) : 0;
+        time_t update_every_s = get_metric_latest_update_every((struct journal_page_header *) (data_start + metric->page_offset));
         update_metric_retention_and_granularity_by_uuid(
                 ctx, &metric->uuid, start_time_s, end_time_s, update_every_s, now_s);