This ticket will modify test_backup26.py so that the 'long' version of the test will take into account the RAM size of the instance it is being run on. Currently the test uses 10,000 tables in 'long' mode, and 500 normally. The 'long' test regularly fails on instances with 32Gb of RAM (eg ubuntu2004-arm-large), and passes on those with 64Gb - see WT-11415 for details.

Testing with 32Gb of RAM indicates that 2500 tables is ok, but 5000 is not.

The test will be modified to use psutil to detect the RAM size, and then use 10,000 tables if there is >32Gb, and 2500 otherwise. This change will mean that the test's behaviour is effectively unchanged on 64Gb instances where it is currently working, and the test can be enabled again on 32Gb instances.

Once a new ubuntu2004-arm instance type with 64b of RAM is available (requested in BUILD-17805), we'll switch to using that instead, and test_backup26 will automatically revert to using 10,000 tables for ubuntu2004-arm.

The ubuntu2004-arm-large instance type has been changed to a 4xlarge to be consistent with ubuntu2004-large and amazon2-arm64-large, meaning all three now have 16 vCPUs and 64Gb of RAM. This means that the change proposed in this ticket to make test_backup26.py adjust itself to the RAM size is now a nice-to-have, not required, so I've reduced the priority to P4.