# C++ driver, exceptions, logs, metrics and timeouts

**URL:** <https://forum.scylladb.com/t/c-driver-exceptions-logs-metrics-and-timeouts/4806>\
**Category:** ScyllaDB\
**Tags:** drivers, troubleshooting, logging, timeout, cplusplus\
**Created:** [May 5, 2025, 3:34am UTC](https://forum.scylladb.com/t/c-driver-exceptions-logs-metrics-and-timeouts/4806 "2025-05-05T03:34:12Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Guy](https://sea2.discourse-cdn.com/flex016/user_avatar/forum.scylladb.com/guy/32/9_2.png) [@Guy](https://forum.scylladb.com/u/Guy)\
**Post date:** [May 5, 2025, 3:34am UTC](https://forum.scylladb.com/t/c-driver-exceptions-logs-metrics-and-timeouts/4806/1 "2025-05-05T03:34:12Z")

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> [@](#):
>
> [**Originally from the User Slack**](https://slack.scylladb.com/)
> 
> ![Nick_Vladiceanu](https://us1.discourse-cdn.com/flex016/uploads/scylladb/original/2X/0/059db617d110231ced9a984559a6da500b22c526.png) **@Nick\_Vladiceanu:** Hey folks  
> we started to observe C++ exceptions in our cluster (Scylla version 5.2), resulting in errors on the clients. Where should we look first, and how can we find the C++ exceptions? Any help appreciated  
> The only unusual logs I find on some of the nodes is
> 
> ```auto
> INFO 2025-04-22 18:13:44,548 [shard 0] reader_concurrency_semaphore - (rate limiting dropped 8931 similar messages) Semaphore _read_concurrency_sem with 36/100 count and 1467312/146381209 memory resources: timed out, dumping permit diagnostics:
> permits	count	memory	table/description/state
> 11	11	496K	system_schema.columns/shard-reader/inactive
> 14	14	470K	system_schema.tables/shard-reader/inactive
> 8	8	360K	system_schema.columns/shard-reader/active/used
> 3	3	102K	system_schema.tables/shard-reader/active/used
> 2	0	5K	system_schema.columns/multishard-mutation-query/active/unused
> 
> ```
> 
> Thanks
> 
> ![avi](https://us1.discourse-cdn.com/flex016/uploads/scylladb/original/1X/b5e08becda8d9df1abff1d3a2d9ffe1126ac3fc6.jpeg) **@avi:** 5.2 is long out of support, please upgrade to a supported version
> 
> ![Nick_Vladiceanu](https://us1.discourse-cdn.com/flex016/uploads/scylladb/original/2X/0/059db617d110231ced9a984559a6da500b22c526.png) **@Nick\_Vladiceanu:** I guess this is a more generic question: where the C++ exceptions can be found? among regular logs?
> 
> ![avi](https://us1.discourse-cdn.com/flex016/uploads/scylladb/original/1X/b5e08becda8d9df1abff1d3a2d9ffe1126ac3fc6.jpeg) **@avi:** Some C++ exceptions (e.g. timeouts) are swallowed by the code and converted into metrics (e.g. timeout metrics). The rest are in the logs.
> 
> ![Nick_Vladiceanu](https://us1.discourse-cdn.com/flex016/uploads/scylladb/original/2X/0/059db617d110231ced9a984559a6da500b22c526.png) **@Nick\_Vladiceanu:** would they appear in the logs for the log level WARN, or require a lower log level? It was a bit difficult to understand what those C++ exceptions were about, no exceptions in the logs.
> 
> ![avi](https://us1.discourse-cdn.com/flex016/uploads/scylladb/original/1X/b5e08becda8d9df1abff1d3a2d9ffe1126ac3fc6.jpeg) **@avi:** WARN or ERROR. They’re likely timeouts. Check the dedicated timeout metrics.