Lock relation used to generate fresh data for RMV.
Lock relation used to generate fresh data for RMV.

The relation should not be accessible to any other process, but it
should be locked for consistency.  Since this is not known to
cause any bug, it will not be back-patch, at least for now.

Per report from Andres Freund

lisakowen/gpdb,xinzweb/gpdb,ovr/postgres-xl,techdragon/Postgres-XL,zeroae/postgres-xl,lisakowen/gpdb,jmcatamney/gpdb,oberstet/postgres-xl,zeroae/postgres-xl,zeroae/postgres-xl,ashwinstar/gpdb,lisakowen/gpdb,oberstet/postgres-xl,lisakowen/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,Postgres-XL/Postgres-XL,adam8157/gpdb,ovr/postgres-xl,greenplum-db/gpdb,50wu/gpdb,pavanvd/postgres-xl,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,xinzweb/gpdb,Postgres-XL/Postgres-XL,ashwinstar/gpdb,ashwinstar/gpdb,xinzweb/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,adam8157/gpdb,yazun/postgres-xl,pavanvd/postgres-xl,yazun/postgres-xl,xinzweb/gpdb,lisakowen/gpdb,lisakowen/gpdb,ashwinstar/gpdb,pavanvd/postgres-xl,pavanvd/postgres-xl,techdragon/Postgres-XL,jmcatamney/gpdb,Postgres-XL/Postgres-XL,techdragon/Postgres-XL,yazun/postgres-xl,oberstet/postgres-xl,50wu/gpdb,ashwinstar/gpdb,techdragon/Postgres-XL,yazun/postgres-xl,50wu/gpdb,adam8157/gpdb,ovr/postgres-xl,jmcatamney/gpdb,ovr/postgres-xl,jmcatamney/gpdb,yazun/postgres-xl,ashwinstar/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,Postgres-XL/Postgres-XL,50wu/gpdb,xinzweb/gpdb,ovr/postgres-xl,adam8157/gpdb,50wu/gpdb,50wu/gpdb,xinzweb/gpdb,jmcatamney/gpdb,oberstet/postgres-xl,xinzweb/gpdb,xinzweb/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,oberstet/postgres-xl,50wu/gpdb,50wu/gpdb,zeroae/postgres-xl,lisakowen/gpdb,techdragon/Postgres-XL,adam8157/gpdb,pavanvd/postgres-xl,adam8157/gpdb,Postgres-XL/Postgres-XL,adam8157/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,zeroae/postgres-xl