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Follow up on #2755 (#3137)

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- don't register secondaries with `noloadbalance` tag.
- mention in the documentation that secondaries are also registered in `pg_dist_node`.
- update docker/kubernetes README files to include examples with secondaries being registered in `pg_dist_node`.
This commit is contained in:
Alexander Kukushkin
2024-08-27 09:34:12 +02:00
committed by GitHub
parent 6d65aa311a
commit 8cdb0c25d9
5 changed files with 172 additions and 135 deletions
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docs/citus.rst
+15 -6
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@@ -138,7 +138,7 @@ An example of :ref:`patronictl_switchover` on the worker cluster::
Citus group: 2
Primary [work2-2]:
Candidate ['work2-1'] []:
When should the switchover take place (e.g. 2022-12-22T08:02 ) [now]:
When should the switchover take place (e.g. 2024-08-26T08:02 ) [now]:
Current cluster topology
+ Citus cluster: demo (group: 2, 7179854924063375386) -+-----------+
| Member | Host | Role | State | TL | Lag in MB |
@@ -147,7 +147,7 @@ An example of :ref:`patronictl_switchover` on the worker cluster::
| work2-2 | 172.27.0.7 | Leader | running | 1 | |
+---------+------------+----------------+---------+----+-----------+
Are you sure you want to switchover cluster demo, demoting current primary work2-2? [y/N]: y
2022-12-22 07:02:40.33003 Successfully switched over to "work2-1"
2024-08-26 07:02:40.33003 Successfully switched over to "work2-1"
+ Citus cluster: demo (group: 2, 7179854924063375386) ------+
| Member | Host | Role | State | TL | Lag in MB |
+---------+------------+---------+---------+----+-----------+
@@ -171,17 +171,26 @@ An example of :ref:`patronictl_switchover` on the worker cluster::
And this is how it looks on the coordinator side::
# The worker primary notifies the coordinator that it is going to execute "pg_ctl stop".
2022-12-22 07:02:38,636 DEBUG: query("BEGIN")
2022-12-22 07:02:38,636 DEBUG: query("SELECT pg_catalog.citus_update_node(3, '172.27.0.7-demoted', 5432, true, 10000)")
2024-08-26 07:02:38,636 DEBUG: query(BEGIN, ())
2024-08-26 07:02:38,636 DEBUG: query(SELECT pg_catalog.citus_update_node(%s, %s, %s, true, %s), (3, '172.19.0.7-demoted', 5432, 10000))
# From this moment all application traffic on the coordinator to the worker group 2 is paused.
# The old worker primary is assiged as a secondary.
2024-08-26 07:02:40,084 DEBUG: query(SELECT pg_catalog.citus_update_node(%s, %s, %s, true, %s), (7, '172.19.0.7', 5432, 10000))
# The future worker primary notifies the coordinator that it acquired the leader lock in DCS and about to run "pg_ctl promote".
2022-12-22 07:02:40,085 DEBUG: query("SELECT pg_catalog.citus_update_node(3, '172.27.0.5', 5432)")
2024-08-26 07:02:40,085 DEBUG: query(SELECT pg_catalog.citus_update_node(%s, %s, %s, true, %s), (3, '172.19.0.5', 5432, 10000))
# The new worker primary just finished promote and notifies coordinator that it is ready to accept read-write traffic.
2022-12-22 07:02:41,485 DEBUG: query("COMMIT")
2024-08-26 07:02:41,485 DEBUG: query(COMMIT, ())
# From this moment the application traffic on the coordinator to the worker group 2 is unblocked.
Secondary nodes
---------------
Starting from Patroni v4.0.0 Citus secondary nodes without ``noloadbalance`` :ref:`tag <tags_settings>` are also registered in ``pg_dist_node``.
However, to use secondary nodes for read-only queries applications need to change `citus.use_secondary_nodes <https://docs.citusdata.com/en/latest/develop/api_guc.html#citus-use-secondary-nodes-enum>`__ GUC.
Peek into DCS
-------------