19cd1cf4b68faff2e29bc2fa884c480e4644cdb4 本次提交变更很多，以Merge PG 12为主。本次提交合并了PG的Disk-based Hash Aggregation功能。

38d88155520790b268b1a380caa9a2d9508edc66 这次提交对pg_stat_activity进行了调整。该修订在GPDB的master分支上，6.X分支没有该修订。

修订说明如下：

pg_stat_activity view gained new 'wait_event' and 'wait_event_type' fields.If a backend is waiting for a lock, disk activity, or some other suchthing, the field shows the reason for the wait. That can be very useful whenanalysing performance issues.
These new fields replace Greenplum's old field, pg_stat_activity.waiting_reason,which was serving a similar purpose. If a backend is waiting for a resourcequeue or group, it is shown in the new wait event fields.

但是，没有说明删除rsgqueueduration字段的原因，比较突兀。