# VTM writer used with Catalyst and large number of processes fails due to excessive memory usage

**URL:** https://discourse.paraview.org/t/vtm-writer-used-with-catalyst-and-large-number-of-processes-fails-due-to-excessive-memory-usage/15629
**Category:** Development
**Tags:** catalyst
**Created:** [October 24, 2024, 1:57pm UTC](https://discourse.paraview.org/t/vtm-writer-used-with-catalyst-and-large-number-of-processes-fails-due-to-excessive-memory-usage/15629 "2024-10-24T13:57:08Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![cmorsbach](https://discourse.paraview.org/user_avatar/discourse.paraview.org/cmorsbach/32/10016_2.png) [@cmorsbach](https://discourse.paraview.org/u/cmorsbach)
#### Post date: [October 24, 2024, 1:57pm UTC](https://discourse.paraview.org/t/vtm-writer-used-with-catalyst-and-large-number-of-processes-fails-due-to-excessive-memory-usage/15629/1 "2024-10-24T13:57:08Z")

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Hi all,  
I’ve been running some strong scaling tests with our CFD code, which has in-situ functionality using ParaView Catalyst V1. The data, we pass to the co-processor is a vtkMultiBlockDataset where only one vtkUnstructuredGrid is populated per MPI process.

I have a simple pipeline, which just writes this dataset as a VTM file. When I scale to a large number of processes (\> 16k), the memory used per process when the pipeline is executed grows with the number of processes until I run out of memory on my compute nodes, although the problem size remains the same.

This does not happen if I use a pipeline where I use a MergeBlocks filter on the dataset and write as PVTU.

In my opinion, this seems as if there is a problem with the VTM writer in ParaView 5.11.2 and 5.12.1. I couldn’t test 5.13.1, yet.

Might be related to [https://gitlab.kitware.com/paraview/paraview/-/issues/22671](https://gitlab.kitware.com/paraview/paraview/-/issues/22671).