We are facing severe memory issues on MySQL instance, running on Azure Database for MySQL flexible server.

Question

We are facing severe memory issues on MySQL instance, running on Azure Database for MySQL flexible server.

Seva Zagorodniy 25

Good day.
We are having memory consumption issues with our MySql Production instance.

Issue details:

Our Server memory consumption grows steadily, and approximately every 20 days Server runs out of memory.

Originally this behavior caused OOM restarts of the server, now we are restarting it manually when the threshold of >95% is reached.

Originally (with default configuration, which was using innodb_buffer_pool_size = 2Gb) it was restarting each 7 days.

The actual problem is that according to all the configuration settings -Server should not require that much memory. And according to all diagnostics of the Server - memory consumption of Database Components does not require these 4 Gigabytes in any way, which ran out regardless of anything, during this 20 days period.

Problem:

We cannot identify what causes that memory consumption, and cannot reproduce same issues on other environments that we have, even of the same Tier.
We need some advisory for identifying, and fixing the root cause for that behavior.

According to our understanding we are facing some memory leakage in components, not directly related to MySql, but rather connected to Azure SaaS. Reason for that assumption is that all MySQL metrics are showing proper memory consumption, which is configured to consume about 70% of the actual memory (now much less, as we have modified innodb pool size).

Details
Instance details:

Deployed on Azure Database for MySQL flexible server
Version: 8.0
Tier: Burstable, B2s, 2 vCores, 4 GiB RAM, 20 storage, 360 IOPS

**Configuration details:
**Pretty much all of the parameters are left as they where configured by the Azure. Including Dynamic. The only notable exception is innodb_buffer_pool_size, which was lowered to 1Gb from the default 2Gb.

tmp_table_size
- 16777216 (16Mb)
innodb_buffer_pool_size
- 1073741824 (1024Mb)
- Actual usage always stays within 1Gb (usually even when server goes OOM it is still around 1010.X Mb)
max_connections
- 341.
- Typically Service is having about 5-20 simultaneous connections opened. 5 for common usage, and about 20 during heaviest ETLs.

Additional details:

Our tables are relying on InnoDB engine.

We do not have locks problems.
We do not have issues with "stalled" transactions.

We do have quite complex queries involved in the Database. But this should be completely irrelevant, as configuration of all related subservices of MySql is such, that it should not consume memory without releasing it anyways.

We have ETLs, which are flushing notable amount of data into that Database, working each hour, and each 12-hour period. We can clearly see the effect of those on InnoDb pages amount, but it acts completely healthy (consumes some pages, then clears some of them). According the available metrics - impact is completely manageable.

Thanks in advance.

Br, Seva.
P.S. This is quite a serious issue for us, as it affects our Prod.

Kalyani Kondavaradala 4,595 Reputation points Microsoft External Staff Moderator

2025-12-02T09:21:48.5166667+00:00
Hi Seva Zagorodniy,

Can you please clarify following things.

Have you observed any specific periods where memory usage spikes?

Are there particular queries or ETL processes that consistently seem to coincide with high memory usage?

What’s the current total number of connections during peak usage, and has that fluctuated recently?

could you please provide the requested details over private messaging to investigate further.

Reference document:

https://learn.microsoft.com/en-us/azure/mysql/flexible-server/how-to-troubleshoot-low-memory-issues
Seva Zagorodniy 25 Reputation points

2025-12-02T12:41:37.1233333+00:00
Good day.

Have you observed any specific periods where memory usage spikes?

No. There are small memory reservation gains during most heaviest ETL runs, which is usually about 0,5-1%. Once a day.
Otherwise memory just steadily grows without any apparent reason.

Are there particular queries or ETL processes that consistently seem to coincide with high memory usage?

No.

What’s the current total number of connections during peak usage,

Quoting:

max_connections

341.

Typically Service is having about 5-20 simultaneous connections opened. 5 for common usage, and about 20 during heaviest ETLs.

and has that fluctuated recently?

No.
We had one huge spike of sessions once, but that was one-time event, and was connected to our API issues. This issue took place only once, and our memory issue is taking place for few months already. Thus - it should not be correlated.

Reference document: https://learn.microsoft.com/en-us/azure/mysql/flexible-server/how-to-troubleshoot-low-memory-issues

We have educated ourselves with that document of course, and have ran all relevant diagnostics mentioned in that document.

As I mentioned before:

According to metrics of MySQL engine - all memory consumption is in check.

According to metrics we do not have problems with connections, or locks, or temp tables.

According to metrics of InnoDb engine (which we use for our Tables) - memory consumption is limited to 25% of total memory of the Instance. And it stays there.

We had though, some problems with bin_files. When this issue first presented itself we had quite high number of those. But after Server restart - this issue went away, but memory issue still persisted.

Br, Seva.
Kalyani Kondavaradala 4,595 Reputation points Microsoft External Staff Moderator

2025-12-02T13:17:06.63+00:00
Hi Seva Zagorodniy,

We had one huge spike of sessions once, but that was one-time event, and was connected to our API issues. This issue took place only once, and our memory issue is taking place for few months already

Could you please help us with:

What was the exact timestamp (including the minute) of the one-time, huge session spike?

The most recent occurrences of the memory issue or any restarts?

Its great that you have already followed the document, can you please provide the requested details over Private messaging.

2 answers

Your answer

Kalyani Kondavaradala 4,595 Reputation points Microsoft External Staff Moderator

2025-12-02T09:21:48.5166667+00:00

Hi Seva Zagorodniy,

Can you please clarify following things.

Have you observed any specific periods where memory usage spikes?

Are there particular queries or ETL processes that consistently seem to coincide with high memory usage?

What’s the current total number of connections during peak usage, and has that fluctuated recently?

could you please provide the requested details over private messaging to investigate further.

Reference document:

https://learn.microsoft.com/en-us/azure/mysql/flexible-server/how-to-troubleshoot-low-memory-issues
Seva Zagorodniy 25 Reputation points

2025-12-02T12:41:37.1233333+00:00

Good day.

Have you observed any specific periods where memory usage spikes?

No. There are small memory reservation gains during most heaviest ETL runs, which is usually about 0,5-1%. Once a day.
Otherwise memory just steadily grows without any apparent reason.

Are there particular queries or ETL processes that consistently seem to coincide with high memory usage?

No.

What’s the current total number of connections during peak usage,

Quoting:

max_connections

341.

Typically Service is having about 5-20 simultaneous connections opened. 5 for common usage, and about 20 during heaviest ETLs.

and has that fluctuated recently?

No.
We had one huge spike of sessions once, but that was one-time event, and was connected to our API issues. This issue took place only once, and our memory issue is taking place for few months already. Thus - it should not be correlated.

Reference document: https://learn.microsoft.com/en-us/azure/mysql/flexible-server/how-to-troubleshoot-low-memory-issues

We have educated ourselves with that document of course, and have ran all relevant diagnostics mentioned in that document.

As I mentioned before:

According to metrics of MySQL engine - all memory consumption is in check.

According to metrics we do not have problems with connections, or locks, or temp tables.

According to metrics of InnoDb engine (which we use for our Tables) - memory consumption is limited to 25% of total memory of the Instance. And it stays there.

We had though, some problems with bin_files. When this issue first presented itself we had quite high number of those. But after Server restart - this issue went away, but memory issue still persisted.

Br, Seva.
Kalyani Kondavaradala 4,595 Reputation points Microsoft External Staff Moderator

2025-12-02T13:17:06.63+00:00

Hi Seva Zagorodniy,

We had one huge spike of sessions once, but that was one-time event, and was connected to our API issues. This issue took place only once, and our memory issue is taking place for few months already

Could you please help us with:

What was the exact timestamp (including the minute) of the one-time, huge session spike?

The most recent occurrences of the memory issue or any restarts?

Its great that you have already followed the document, can you please provide the requested details over Private messaging.

Answer 1

Hi Seva Zagorodniy,

Following upon our discussion over Private messaging

While investigating on the issue, we have identified a high number of slow-running queries (500 to 1000). These queries are significantly contributing to the increased memory consumption and overall performance degradation.

We would also like to highlight that the current server configuration is a burstable SKU, which is generally recommended only for non-production or light workloads. For stable performance in production environments, especially under consistent or heavy load, we recommend upgrading to a General Purpose edition. This will help prevent performance issues and ensure smoother operation of your workload.

Reference document:

Service Tiers - Azure Database for MySQL | Microsoft Learn

User's image I hope this has been helpful!

Kindly consider upvoting and accepting the answer if the given information answers your query. If you still have questions, please let us know what is needed in the comments so the question can be answered

Thanks,

Kalyani

Kalyani Kondavaradala 4,595 Reputation points Microsoft External Staff Moderator

2025-12-05T09:42:57.3833333+00:00

Hi Seva Zagorodniy,

Just checking to see if you have a chance to check my previous response and helped, do let me know if you have any further questions on this.

Answer 2

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We are facing severe memory issues on MySQL instance, running on Azure Database for MySQL flexible server.

2 answers

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