Update libmetrics docs to cover some recent questions and issues.
Review URL: http://codereview.chromium.org/2828017
diff --git a/metrics/README b/metrics/README
index 4219379..677e6b7 100644
--- a/metrics/README
+++ b/metrics/README
@@ -116,3 +116,36 @@
daemon. Then the metrics daemon needs to monitor for the relevant
events and take appropriate action -- for example, aggregate data and
send the histogram samples.
+
+
+================================================================================
+FAQ
+================================================================================
+
+Q. What should my histogram's |min| and |max| values be set at?
+
+A. You should set the values to a range that covers the vast majority
+ of samples that would appear in the field. Note that samples below
+ the |min| will still be collected in the underflow bucket and
+ samples above the |max| will end up in the overflow bucket. Also,
+ the reported mean of the data will be correct regardless of the
+ range.
+
+Q. How many buckets should I use in my histogram?
+
+A. You should allocate as many buckets as necessary to perform proper
+ analysis on the collected data. Note, however, that the memory
+ allocated in Chrome for each histogram is proportional to the
+ number of buckets. Therefore, it is strongly recommended to keep
+ this number low (e.g., 50 is normal, while 100 is probably high).
+
+Q. When should I use an enumeration (linear) histogram vs. a regular
+ (exponential) histogram?
+
+A. Enumeration histograms should really be used only for sampling
+ enumerated events and, in some cases, percentages. Normally, you
+ should use a regular histogram with exponential bucket layout that
+ provides higher resolution at the low end of the range and lower
+ resolution at the high end. Regular histograms are generally used
+ for collecting performance data (e.g., timing, memory usage, power)
+ as well as aggregated event counts.