gp数据库vacuum语句长时间执行未结束，导致数据库表一直被锁，数据无法入库

这个情况之前也出现过，当时直接通过pg_cancel_backend把vacuum语句cancel掉了，最近再次出现。

查看两次问题出现时间点的GP库日志发现均有如下的异常信息，想请教一下各位这个异常是什么？是否对vacuum的执行有影响？

2017-11-21 01:06:53.934386 CST,"ossdbuser","utrafficdb",p67297,th1654146848,"127.0.0.1","48822",2017-09-27 17:05:42 CST,0,con39,cmd3254774,seg-1,,,,,"LOG","00000","Migrating all allocated memory chunks to generation 0 due to generation counter exhaustion and QE recycling",,,,,,,0,,"memaccounting.c",1163,