Summary:
For now, disable it since the below command indicates it can cause a
failure. Running that command with `-experimental_mempurge_threshold=0`
has been running successfully for several minutes, whereas before it
failed in seconds.
```
$ while rm -rf /dev/shm/single_stress && ./db_stress --clear_column_family_one_in=0 --column_families=1 --db=/dev/shm/single_stress --experimental_mempurge_threshold=5.493146827397074 --flush_one_in=10000 --reopen=0 --write_buffer_size=262144 --value_size_mult=33 --max_write_buffer_number=3 -ops_per_thread=10000; do : ; done
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8958
Reviewed By: ltamasi
Differential Revision: D31187059
Pulled By: ajkr
fbshipit-source-id: 04d5bfb4fcc4f5b66233e691427dfd940c67037f
6d424be910