Hard Out Of Memory Error. Bucket "xxx" inusual use of RAM process memcached

Infrastructure
32GB RAM
64GB HDD
2 couchbase nodes version 4.5.1
2 Sync gateway version 1.3.1

recently the console of couchbase display next error
Hard Out Of Memory Error. Bucket “xxx” All memory allocated to this bucket is used for metadata.

i saw the details of server node in RAM section and i detected 18Gb with label Other Data

i went to my linux and typed command top, i sorted by RAM

Questions :

What is the memcached process and why use a lot of RAM?
There is form to reduce consume of RAM ?
does any workaround ?