tonysun83 commented on a change in pull request #1432: Support callback module
data provider
URL: https://github.com/apache/couchdb/pull/1432#discussion_r202256855
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File path: src/couch_epi/README.md
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@@ -65,6 +66,38 @@ There are also additional functions to get the same data in
various formats
- `couch_epi:keys(Handle)` - returns list of configured keys
- `couch_epi:subscribers(Handle)` - return list of known subscribers
+The difference between `static_module` and `callback_module` providers is in
how
+couch_epi detects the changes. `static_module` is designed for the cases when
you
+have your data hardcoded in the module. For example you might have the
following:
+
+```
+-export([data/0]).
+
+data() ->
+ [
+ {[complex, key, 2], [
+ {type, counter},
+ {desc, bar}
+ ]},
+ {[complex, key, 1], [
+ {type, counter},
+ {desc, updated_foo}
+ ]}
+ ].
+```
+
+The changes are detected by relying on `vsn` module attribute. Therefore we
+would notice the change only when data source module is recompiled.
+
+The `callback_module` provider uses the return value from `data/0` to detect
+changes and it is useful for cases when the data term is constructed
dynamically.
+For example to cache values of CouchDB config one could use the following:
+
+```
+-export([data/0]).
+data() ->
+ config:get("dreyfus").
Review comment:
change this to ```config:get("dreyfus", "foo")```?
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