Summary:

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This feature supply a way to monitor thd or query memory usage.

Memory_used display current thread memory that allocated.

Query_memory_used display current thd->query() memory that allocated.

Notes:

  Memory_used is added when malloc and substracted when free.

  Query_memory_used is added when malloc and reset when query end.

Usage:

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1. show status like '%memory_used%'

2. show full processlist;