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[doc][2024.2.1] Added limitations for YSQL Connection Manager #25458

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[doc][2024.2.1] Added limitations for YSQL Connection Manager #25458

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Limitations for conn mgr
rahulb-yb Dec 31, 2024
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rahulb-yb Jan 9, 2025
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rahulb-yb Jan 9, 2025
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rahulb-yb Jan 10, 2025
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Update docs/content/stable/explore/going-beyond-sql/connection-mgr-ys…
ddhodge Jan 10, 2025
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10 changes: 10 additions & 0 deletions docs/content/stable/explore/going-beyond-sql/connection-mgr-ysql.md
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Expand Up @@ -97,3 +97,13 @@ The following table describes YB-TServer flags related to YSQL Connection Manage
| ysql_conn_mgr_server_lifetime | The maximum duration (in seconds) that a backend PostgreSQL connection managed by YSQL Connection Manager can remain open after creation. | 3600 |
| ysql_conn_mgr_log_settings | Comma-separated list of log settings for YSQL Connection Manger. Can include 'log_debug', 'log_config', 'log_session', 'log_query', and 'log_stats'. | "" |
| ysql_conn_mgr_use_auth_backend | Enable the use of the auth-backend for authentication of logical connections. When false, the older auth-passthrough implementation is used. | true |

## Limitations

- Changes to default GUC values for a user or database (ALTER ROLE SET/ALTER DATABASE SET queries) may reflect in other pre-existing active sessions.
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can you be more specific? only flags, not YSQL configuration parameters, are listed above - so what values are you talking about?

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GUC values have nothing to do with anything previously mentioned on this page; this category of session-specific database objects may not have the correct behaviour when using connection manager as per the limitation I have mentioned. I also use the term "may" on this line because trying to explain the scenario(s) where this behaviour can be seen would dive into too many technical details for what is a very rare corner case.

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- Connection Manager can only support upto a total of 10,000 pools to route. This includes pools corresponding to dropped users and databases as well.
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is this simultaneous, or what exactly?

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not simultaneous - Connection Manager can route upto 10,000 unique connection pools over its lifetime as a process. As of now, there is no capability to "clean up" the history of pools for "dead" routes corresponding to users or databases that do not exist

- Prepared statements may be visible to other sessions within the same connection pool. [#24652](https://github.com/yugabyte/yugabyte-db/issues/24652)
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- Attempting to use DEALLOCATE/DEALLOCATE ALL queries can result in unexpected behavior. [#24653](https://github.com/yugabyte/yugabyte-db/issues/24653)
- As of now, Connection Manager does not facilitate custom configurations per pool. All configurations used will apply to every pool that Connection Manager routes through.
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- With connection manager enabled, the backend PID stored using JDBC drivers may not accurate. This does not affect backend-specific functionalities (eg. cancel queries), but this PID should not be used to identify the backend process.
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tracking issue?

- `currval` and `nextval` functions do not work by default with connection manager enabled. They can be supported with the help of the `ysql_conn_mgr_sequence_support_mode` flag.
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@ddhodge ddhodge Jan 5, 2025 •
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- `currval` and `nextval` functions do not work by default with connection manager enabled. They can be supported with the help of the `ysql_conn_mgr_sequence_support_mode` flag.
- By default, `currval` and `nextval` functions do not work when YSQL Connection Manager is enabled. To support these functions, use the `ysql_conn_mgr_sequence_support_mode` flag.

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the ysql_conn_mgr_sequence_support_mode is not a boolean flag, I can try to incorporate this comment in a similar fashion

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I changed the suggested text slightly

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