Re: [HACKERS] [PATCH v1] Add and report the new "in_hot_standby" GUC pseudo-variable.
| От | Melanie Plageman |
|---|---|
| Тема | Re: [HACKERS] [PATCH v1] Add and report the new "in_hot_standby" GUC pseudo-variable. |
| Дата | |
| Msg-id | CAAKRu_ad5BYjMi8Qrinp8kih5++AXxOSvB8wMy8Jt8pBd-wNTg@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: [HACKERS] [PATCH v1] Add and report the new "in_hot_standby" GUC pseudo-variable. (Melanie Plageman <melanieplageman@gmail.com>) |
| Ответы |
Re: [HACKERS] [PATCH v1] Add and report the new "in_hot_standby" GUC pseudo-variable.
|
| Список | pgsql-hackers |
On Tue, Sep 19, 2017 at 4:15 PM, Melanie Plageman <melanieplageman@gmail.com> wrote:
Hi Elvis,The latest patch applies cleanly and builds (I am also seeing the failing TAP tests), however, I have a concern. With a single server set up, when I attempt to make a connection with target_session_attrs=read-write, I get the message psql: could not make a suitable connection to server "localhost:5432"Whereas, when I attempt to make a connection with target_session_attrs=read-only, it is successful. I might be missing something, but this seems somewhat counter-intuitive. I would expect to specify read-write as target_session_attrs and successfully connect to a server on which read and write operations are permitted. I see this behavior implemented in src/interfaces/libpq/fe-connect.c Is there a reason to reject a connection to a primary server when I specify 'read-write'? Is this intentional?
Making an assumption about the intended functionality mentioned above, I swapped the 'not' to the following lines of src/interfaces/libpq/fe-connect.c ~ line 3005
if (conn->target_session_attrs != NULL &&
((strcmp(conn->target_session_attrs, "read-write") == 0 && conn->session_read_only) ||
(strcmp(conn->target_session_attrs, "read-only") == 0 && !conn->session_read_only)))
I rebased and built with this change locally.
The review below is based on the patch with that change.
Also, the following comment has what looks like a copy-paste error and the first line should be deleted
in src/backend/utils/misc/guc.c ~ line 10078
assign_default_transaction_read_only
+assign_default_transaction_read_only(bool newval, void *extra)
...
+ /*
- * We clamp manually-set values to at least 1MB. Since
+ * Also set the session read-only parameter. We only need
+ * to set the correct value in processes that have database
+ * sessions, but there's no mechanism to know that there's
patch applies cleanly: yes
installcheck: passed
installcheck-world: passed
feature works as expected: yes (details follow)
With two servers, one configured as the primary and one configured to run in Hot Standby mode, I was able to observe that the value of session_read_only changed after triggering failover once the standby server exited recovery
When attempting to connect to a primary server with target_session_attrs=read-write, I was successful and when attempting to connect with target_session_attrs=read-only, the connection was closed and the expected message was produced
Thanks!
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