Step 3:
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Preserve worker pool information on either STOP SLAVE/Error. In case STOP
SLAVE is executed worker threads will be gone, hence worker threads will be
unavailable. Querying the table at this stage will give empty rows. To
address this case when worker threads are about to stop, due to an error or
forced stop, create a backup pool and preserve the data which is relevant to
populate performance schema table. Clear the backup pool upon slave start.
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