garrensmith commented on a change in pull request #2410: Mango metrics
URL: https://github.com/apache/couchdb/pull/2410#discussion_r364260299
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File path: src/mango/src/mango_cursor.erl
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@@ -146,44 +146,87 @@ group_indexes_by_type(Indexes) ->
end, ?CURSOR_MODULES).
-maybe_add_warning(UserFun, #cursor{index = Index, opts = Opts}, UserAcc) ->
- NoIndexWarning = case Index#idx.type of
- <<"special">> ->
- <<"no matching index found, create an index to optimize query
time">>;
+% warn if the _all_docs index was used to fulfil a query
+no_index_warning(#idx{type = Type}) when Type =:= <<"special">> ->
+ couch_stats:increment_counter([mango, unindexed_queries]),
+ [<<"No matching index found, create an index to optimize query time.">>];
+no_index_warning(_) ->
+ [].
+
+
+% warn if user specified an index which doesn't exist or isn't valid
+% for the selector.
+% In this scenario, Mango will ignore the index hint and auto-select an index.
+invalid_index_warning(Index, Opts) ->
+ UseIndex = lists:keyfind(use_index, 1, Opts),
+ invalid_index_warning_int(Index, UseIndex).
+
+
+invalid_index_warning_int(Index, {use_index, [DesignId]}) ->
+ case filter_indexes([Index], DesignId) of
+ [] ->
+ couch_stats:increment_counter([mango, query_invalid_index]),
+ Reason = fmt("_design/~s was not used because it does not contain
a valid index for this query.",
+ [ddoc_name(DesignId)]),
+ [Reason];
_ ->
- ok
- end,
+ []
+ end;
+invalid_index_warning_int(Index, {use_index, [DesignId, ViewName]}) ->
+ case filter_indexes([Index], DesignId, ViewName) of
+ [] ->
+ couch_stats:increment_counter([mango, query_invalid_index]),
+ Reason = fmt("_design/~s, ~s was not used because it is not a
valid index for this query.",
+ [ddoc_name(DesignId), ViewName]),
+ [Reason];
+ _ ->
+ []
+ end;
+invalid_index_warning_int(_, _) ->
+ [].
- UseIndexInvalidWarning = case lists:keyfind(use_index, 1, Opts) of
- {use_index, []} ->
- NoIndexWarning;
- {use_index, [DesignId]} ->
- case filter_indexes([Index], DesignId) of
- [] ->
- fmt("_design/~s was not used because it does not contain a
valid index for this query.",
- [ddoc_name(DesignId)]);
- _ ->
- NoIndexWarning
- end;
- {use_index, [DesignId, ViewName]} ->
- case filter_indexes([Index], DesignId, ViewName) of
- [] ->
- fmt("_design/~s, ~s was not used because it is not a valid
index for this query.",
- [ddoc_name(DesignId), ViewName]);
- _ ->
- NoIndexWarning
- end
- end,
- maybe_add_warning_int(UseIndexInvalidWarning, UserFun, UserAcc).
+% warn if a large number of documents needed to be scanned per result
+% returned, implying a lot of in-memory filtering
+index_scan_warning(#execution_stats {
+ totalDocsExamined = Docs,
+ totalQuorumDocsExamined = DocsQuorum,
+ resultsReturned = ResultCount
+ }) ->
+ % Docs and DocsQuorum are mutually exclusive so it's safe to sum them
+ DocsScanned = Docs + DocsQuorum,
+ Ratio = index_scan_ratio(DocsScanned, ResultCount),
+ Threshold = config:get("mango", "index_scan_warning_threshold", 10),
+ index_scan_warning_int(Threshold, Ratio).
-maybe_add_warning_int(ok, _, UserAcc) ->
- UserAcc;
+index_scan_ratio(DocsScanned, 0) ->
+ DocsScanned;
+index_scan_ratio(DocsScanned, ResultCount) ->
+ DocsScanned / ResultCount.
-maybe_add_warning_int(Warning, UserFun, UserAcc) ->
- couch_stats:increment_counter([mango, unindexed_queries]),
- Arg = {add_key, warning, Warning},
+
+index_scan_warning_int(Threshold, Ratio) when is_integer(Threshold), Threshold
> 0, Ratio > Threshold ->
+ couch_stats:increment_counter([mango, too_many_docs_scanned]),
+ Reason = <<"The number of documents examined is high in proportion to the
number of results returned. Consider adding a more specific index to improve
this.">>,
+ [Reason];
+index_scan_warning_int(_, _) ->
+ [].
+
+
+maybe_add_warning(UserFun, #cursor{index = Index, opts = Opts}, Stats,
UserAcc) ->
+ W0 = invalid_index_warning(Index, Opts),
+ W1 = no_index_warning(Index),
+ W2 = index_scan_warning(Stats),
+ Warnings = lists:append([W0, W1, W2]),
+ maybe_add_warning_int(Warnings, UserFun, UserAcc).
+
+
+maybe_add_warning_int([], _, UserAcc) ->
Review comment:
Can you move this function above all the functions that it calls. That makes
it easier to follow.
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