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Add comments from code walkthrough

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commit c39d74bbfd6a5c420ff38826674f7332b43b955e 1 parent de6f1c6
Noah Gibbs noahgibbs authored
Showing with 13 additions and 0 deletions.
  1. +13 −0 lib/hastur-server/api/helpers.rb
13 lib/hastur-server/api/helpers.rb
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@@ -305,6 +305,15 @@ def query_hastur_by_labels(params)
data = Hastur::Cassandra.lookup_label_timestamps(cass_client, data, must_not.keys,
start_ts, end_ts)
+ # This is the very final row-key/column-key query to Cassandra. When you add a "count"
+ # type that can be returned, you'll stop really doing this query and just count the
+ # column keys.
+ #
+ # Also, this is why getting a big chunk of data distributed randomly throughout your
+ # total dataset is really, really slow. This is not an operation Cassandra does
+ # quickly. If you want that, you'll need to get *all* data and filter out the wanted
+ # columns for yourself -- which will also be slow, naturally.
+ #
result = query_row_col_from_cassandra(data, start_ts, end_ts)
end
@@ -406,6 +415,7 @@ def uuid_or_hostname_to_uuids(nodes)
# node registration is daily, bucket the lookup on day boundary if unspecified
day_start_ts, day_end_ts = get_start_end :one_day
+ # You know, this could be sped up a *lot* by caching. Just sayin'.
uuid_lookup = Hastur::Cassandra.lookup_by_key(cass_client, "host-uuid", day_start_ts, day_end_ts)
nodes.flatten.map do |maybe_uuid|
@@ -472,6 +482,9 @@ def deserialize_json_messages(data)
end
# MultiJson gets really upset if you ask it to decode a ruby Hash that ends up
# being stringified - TODO(al,2012-06-21) figure out why hashes are appearing in this data
+
+ # Hashes are appearing in this data when you request *both* a rollup and normal data
+ # together. The right answer is probably not to do that (i.e. change the API).
unless value.kind_of? String
logger.debug "BUG: Got a ruby #{value.class} where a JSON string was expected: #{value.inspect}"
next
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