# 一、功能

## Disk-based Hash Aggregation

[19cd1cf4b68faff2e29bc2fa884c480e4644cdb4](https://github.com/greenplum-db/gpdb/commit/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。

# 二、疑问

## pg_stat_activity为何删除rsgqueueduration字段

[38d88155520790b268b1a380caa9a2d9508edc66](https://github.com/greenplum-db/gpdb/commit/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 such
> thing, the field shows the reason for the wait. That can be very useful when
> analysing 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 resource
> queue 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。