我们用来从暂存表中将数据加载到事实表中的简单 "INSERT INTO ... SELECT * FROM" 从需要大约 5 秒变成了需要 20 多分钟。
因此,我放弃了所有预加入投影,并尝试使用数据库设计师来设计特定于查询的投影,但这还不够。即使有了这些投影,一个简单的联接也需要大约 14 秒,而使用预加入投影只需要大约 1 秒。
我的问题是:预加入投影会使数据插入如此缓慢是否正常,如果不是,可能的原因是什么? 如果正常的话,那对我们来说就是个致命问题,有哪些其他技术可以加速联接?
我们在 5 节点集群上运行 Vertica,每个节点都有 2 个四核 CPU 和 32 GB 内存。 我的示例查询中的表分别具有 188,843,085 和 25,712,878 行。
EXPLAIN 输出如下:
EXPLAIN SELECT referer_via_.url as referralPageUrl, COUNT(DISTINCT sessio
n.id) as visits FROM owa_session as session JOIN owa_referer AS referer_vi
a_ ON session.referer_id = referer_via_.id WHERE session.yyyymmdd BETWEEN
'20121123' AND '20121123' AND session.site_id = '49' GROUP BY referer_via_
.url ORDER BY visits DESC LIMIT 250;
Access Path:
+-SELECT LIMIT 250 [Cost: 1M, Rows: 250 (STALE STATISTICS)] (PATH ID: 0)
| Output Only: 250 tuples
| Execute on: Query Initiator
| +---> SORT [Cost: 1M, Rows: 1 (STALE STATISTICS)] (PATH ID: 1)
| | Order: count(DISTINCT "session".id) DESC
| | Output Only: 250 tuples
| | Execute on: All Nodes
| | +---> GROUPBY PIPELINED (RESEGMENT GROUPS) [Cost: 1M, Rows: 1 (STALE
STATISTICS)] (PATH ID: 2)
| | | Aggregates: count(DISTINCT "session".id)
| | | Group By: referer_via_.url
| | | Execute on: All Nodes
| | | +---> GROUPBY HASH (SORT OUTPUT) (RESEGMENT GROUPS) [Cost: 1M, Rows
: 1 (STALE STATISTICS)] (PATH ID: 3)
| | | | Group By: referer_via_.url, "session".id
| | | | Execute on: All Nodes
| | | | +---> JOIN HASH [Cost: 1M, Rows: 1 (STALE STATISTICS)] (PATH ID:
4) Outer (RESEGMENT)
| | | | | Join Cond: ("session".referer_id = referer_via_.id)
| | | | | Execute on: All Nodes
| | | | | +-- Outer -> STORAGE ACCESS for session [Cost: 463, Rows: 1 (ST
ALE STATISTICS)] (PUSHED GROUPING) (PATH ID: 5)
| | | | | | Projection: public.owa_session_projection
| | | | | | Materialize: "session".id, "session".referer_id
| | | | | | Filter: ("session".site_id = '49')
| | | | | | Filter: (("session".yyyymmdd >= 20121123) AND ("session"
.yyyymmdd <= 20121123))
| | | | | | Execute on: All Nodes
| | | | | +-- Inner -> STORAGE ACCESS for referer_via_ [Cost: 293K, Rows:
26M] (PATH ID: 6)
| | | | | | Projection: public.owa_referer_DBD_1_seg_Potency_2012112
2_Potency_20121122
| | | | | | Materialize: referer_via_.id, referer_via_.url
| | | | | | Execute on: All Nodes
(STALE STATISTICS)
这样的提示会让我非常担心。你尝试更新统计信息了吗? - user330315public.owa_referer_DBD_1_seg_Potency_2012112
上缺乏筛选器。我提高查询性能的第一步是确保所有投影都应用了最大数量的筛选器。 - QuinnG