jsrrdgraph: Improve performance for graphs in the future

The RRD file has finer details for more recent data points. When looking
for a match for a graph past the last update ("the future"), a RRA would
be picked which has a step size of 1. As we know that no data points are
available, optimise this and return earlier with the full range set to
NaN.

1 files changed, 14 insertions, 2 deletions

diff --git a/js/RrdDataFile.js b/js/RrdDataFile.js
index 08cc3ae..4f96234 100644
--- a/js/RrdDataFile.js
+++ b/js/RrdDataFile.js
@@ -49,6 +49,7 @@ RrdDataFile.prototype = {
                 var rows;
                 var rra;
                 var i, ii;
+                var last_update = rrd.getLastUpdate();
 
                 var cf_idx = gdp.cf;
                 var ds_cnt = rrd.getNrDSs();
@@ -57,12 +58,23 @@ RrdDataFile.prototype = {
                 for (i = 0; i < ds_cnt; i++)
                         gdp.ds_namv[i] = rrd.rrd_header.getDSbyIdx(i).getName();
 
+                /* if the requested graph starts after the last available data point,
+                 * return one big NaN instead of taking the finest (step=1) RRA */
+                if (gdp.start > last_update) {
+                        ft_step = gdp.end - gdp.start;
+                        gdp.ds_cnt = ds_cnt;
+                        gdp.data = [];
+                        for (ii = 0; ii < ds_cnt; ii++)
+                                gdp.data[ii] = Number.NaN;
+                        return ft_step;
+                }
+
                 for (i = 0; i < rra_cnt; i++) {
                         rra = rrd.getRRAInfo(i);
                         if (RrdGraphDesc.cf_conv(rra.getCFName()) === cf_idx) {
                                 /* covered seconds in this RRA */
                                 var range_secs = rra.getStep();
-                                cal_end = rrd.getLastUpdate() - (rrd.getLastUpdate() % range_secs);
+                                cal_end = last_update - (last_update % range_secs);
                                 cal_start = cal_end - (range_secs * rra.row_cnt);
                                 full_match = gdp.end - gdp.start;
 
@@ -101,7 +113,7 @@ RrdDataFile.prototype = {
                 gdp.ds_cnt = ds_cnt;
                 data_ptr = 0;
 
-                var rra_end_time = (rrd.getLastUpdate() - (rrd.getLastUpdate() % ft_step));
+                var rra_end_time = (last_update - (last_update % ft_step));
                 var rra_start_time = (rra_end_time - (ft_step * (rra_info.row_cnt - 1)));
                 /* here's an error by one if we don't be careful */
                 var start_offset = (gdp.start + ft_step - rra_start_time) / ft_step;