Cluster re-sync causes much lock

Hello,

We have a 3-nodes Percona Xtradb Cluster running 5.7.x version with a 300 Go dataset.
We had a crash this afternoon but this is not the issue.

We restarted the whole cluster with single node (boostrap mode), that works.

Then when the second node joins (xtrabackup-v2 method), everything goes fine during the first 200 GB, then the running node stops serving queries and piles-up INSERTS/UPDATE against certain tables (InnoDB) with this state :

wsrep: initiating pre-commit for write set (2493327) 

Is that expected behaviour? How to prevent that and maintain MySQL service available during resync?

config :

wsrep_provider=/usr/lib/galera3/libgalera_smm.so
wsrep_cluster_address=gcomm://
wsrep_slave_threads=16
wsrep_log_conflicts
wsrep_node_address=xxxx
wsrep_sst_donor=xxxx
wsrep_cluster_name=xxxx
#If wsrep_node_name is not specified,  then system hostname will be used
#wsrep_node_name=
wsrep_sst_method=xtrabackup-v2
wsrep_sst_auth="sstuser:xxxx"
wsrep_replicate_myisam=ON

Thanks,

Gaëtan

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