FME Memory management

It may be worth checking how FME is calculating ‘virtual memory’ here, as it may not correspond directly to the value shown by Windows. The 255.98 GB could represent available virtual address space rather than the amount the system can actually commit.

I’d suggest that you confirm this with FME support before assuming the figure is used for memory optimisation.

​@sharon_43 Thanks. I was wondering if one of the safe support would be on here :) 

One additional observation suggests that FME isn't just reporting 255.98 GB of virtual memory available and using that value to derive its memory management thresholds:

• Start freeing memory when process exceeds 191.98 GB
• Stop freeing memory when process falls below 143.99 GB

As the same AVD host reports approximately 64 GB RAM and 73.5 GB virtual memory in Windows System Information, FME could be overestimating available memory in a multi-session environment and delaying memory optimisation during large jobs.

Hi ​@andrewj74! Thanks for opening a support case and for sharing those memory-threshold details. We’ll update this thread as soon as we have more information.

Thank you for raising this! 🙂
 

Hey ​@andrewj74. We appreciate your patience. For anyone who has a similar use case, it is currently on our radar and we’ll update you as soon as we have more information. Thanks.

Just an update based on the test:  FME is not actually using the reported 255.98 GB available virtual memory or 191.98 GB memory-release threshold in the way initially assumed. In practice, FME began reporting “Resource Manager: Optimizing Memory Usage” when the process reached around 55–60 GB committed memory, which is consistent with the actual 73.5 GB total virtual memory available on the AVD.

I guess the question is just why FME reports the much higher virtual-memory values, where those values come from and what those figures actually represent. Thanks for looking into this.

I think that Virtual memory value in FME is an uncapped limit that regardless of how much memory is committed FME will not exceed this. It’s 4 times the amount of physical memory. 255.98 GB = 63.99 GB * 4.

• Start freeing memory when process exceeds 191.98 GB = 63.99 * 3
• Stop freeing memory when process falls below 143.99 GB = 63.99 * 3 * 0.75

The important number to look at is the amount of committed vs total available. Total available being your RAM plus the pagefile. 

What I’ve found in practice is that FME (FME 2025) will commit memory until 85% of the total virtual memory is used up at which point it will start Optimizing. From my observations the Optimizing does not actually always reduce the amount of committed memory by much (if at all) compared with the actual working set (that’s based on a handful of observations so it might vary quite a lot between processes).  

I have the situation now where FME has Committed about 30GB or memory in one process, however, it’s actively only using about 8. Other processes are using the remaining 22GB of memory. My machine still have about 30 GB of free RAM but because the % of commited memory is at the limit FME is Optimizing, All other FME processes running at the same time also use the same limit and so also start to Optimize. Even though there is still 30GB of memory available to use.

 

If I were to increase the size of my virtual memory by increasing the pagefile then the amount of committed memory possible will go up and FME would not need to optimize, however, then you run into the risk of overcommitting significantly and Windows has to swap which is probably much worse than FME Optimizing (which is why I assume FME Does it in the first place).

I’m not sure if FME 2026 has different memory management compared with 2026 but it may.