albertogpz commented on code in PR #7861:
URL: https://github.com/apache/geode/pull/7861#discussion_r983280085
##########
geode-docs/developing/data_serialization/PDX_Serialization_Features.html.md.erb:
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@@ -31,6 +31,33 @@ When you serialize an object using PDX,
<%=vars.product_name%> stores the object
This centralization of object type information is advantageous for
client/server installations in which clients and servers are written in
different languages. Clients pass registry information to servers automatically
when they store a PDX serialized object. Clients can run queries and functions
against the data in the servers without compatibility between server and the
stored objects. One client can store data on the server to be retrieved by
another client, with no requirements on the part of the server.
+**Note:**
+There are situations where some of the information in the central registry of
the PDX domain object metadata is lost, e.g. when restoring an old backup with
an outdated central registry.
+
+When that happens, new clients connecting to the cluster for the first time
will get outdated PDX type information from the central registry, but, since
information in the central registry is cached by clients, old clients may have
fresher information about PDX types than the central registry does. That will
result into inconsistent information about PDX types spread across the system:
+
+- old clients have fresh information
+- the central registry has outdated information
+- new clients have outdated information
+
+If old clients write entries of a PDX type they know but the central registry
doesn't, new clients will get "Unknown PDX type" errors when they read those
objects.
+
+To avoid this problem, clients may be configured with the system property in
the table below to clear their PDX type cache when they disconnect from the
cluster. After clearing their cache, old clients will re-generate type
information for all PDX types, including the types the central registry
"forgot". Since new PDX type information will be written in the central
registry before entries of that type are written in the cluster, the central
registry and all clients, old and new, will store consistent PDX type
information.
+
+| Name | Description
| Default |
+|-------------------------------------------|---------------------------------------------------------|---------|
+| `gemfire.ON_DISCONNECT_CLEAR_PDXTYPEIDS` | Clear pdxType ids when client
disconnects from servers. | `false` |
+- In the API, set the System properties before the cache creation call.
Example:
+
+ ``` pre
+ System.setProperty(PoolImpl.ON_DISCONNECT_CLEAR_PDXTYPEIDS, "true");
+ ```
+- At the java command line, pass in System properties using the -D switch.
Example:
+
+ ``` pre
+ java -Dgemfire.ON_DISCONNECT_CLEAR_PDXTYPEIDS=true
+ ```
+
Review Comment:
It would probably be better to add this variable and description to the
corresponding documents of the Java and Native clients:
https://geode.apache.org/docs/geode-native/cpp/115/configuring/sysprops.html
https://geode.apache.org/docs/guide/115/reference/topics/gemfire_properties.html
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