BUG #14404: High row estimates when query uses master inherited tables

The following bug has been logged on the website:

Bug reference: 14404
Logged by: Clinton Adams
Email address: clinton(dot)adams(at)gmail(dot)com
PostgreSQL version: 9.6.1
Operating system: centos 7, 4.3.0-1.el7.elrepo.x86_64 #1 SMP Tue Nov
Description:

Row estimates are way off (406484054678631 vs 38) when using master
partition tables. If I change the query to go directly against one child
table, estimates and query time are in line with what I expect.

Issue occurs on 9.6.1, all tables analyzed. Row counts per child table
(sensorcore8, coredetail8, etc) are 126340588 each.

Issue does not occur on 9.4.6 (do not have 9.5 handy to test atm).

--
-- Plan with high estimate
--
EXPLAIN
SELECT core.sensorcoreid
FROM sensor.sensorcore core

JOIN sensor.coredetail cored ON cored.typeid = core.typeid AND
cored.sensorcoreid = core.sensorcoreid
JOIN sensor.corefilldetail corefd ON corefd.typeid = core.typeid AND
corefd.sensorcoreid = core.sensorcoreid
WHERE
core.typeid = 8 AND core.sensorid = 1814821;
QUERY PLAN

-----------------------------------------------------------------------------------------------------------------------------------
Merge Join (cost=5.62..57175008.37 rows=406484054678631 width=4)
Merge Cond: (corefd.sensorcoreid = cored.sensorcoreid)
-> Merge Append (cost=2.81..28268953.91 rows=126340593 width=8)
Sort Key: corefd.sensorcoreid
-> Index Scan using ix_corefilldetail on corefilldetail corefd
(cost=0.50..3.59 rows=1 width=8)
Filter: (typeid = 8)
-> Index Scan using ix_corefilldetail8 on corefilldetail8 corefd_1
(cost=2.27..21951920.63 rows=126340592 width=8)
Filter: (typeid = 8)
-> Materialize (cost=2.81..16349690.36 rows=125477313 width=12)
-> Nested Loop (cost=2.81..15094917.23 rows=125477313 width=12)
-> Merge Append (cost=2.81..15094701.36 rows=39 width=8)
Sort Key: core.sensorcoreid
-> Index Scan using pk_sensorcore on sensorcore core
(cost=0.50..3.60 rows=1 width=8)
Filter: ((typeid = 8) AND (sensorid = 1814821))
-> Index Scan using sensor_sensorcore8_pkey on
sensorcore8 core_1 (cost=2.27..15094695.77 rows=38 width=8)
Filter: ((typeid = 8) AND (sensorid = 1814821))
-> Append (cost=0.00..5.38 rows=2 width=8)
-> Seq Scan on coredetail cored (cost=0.00..0.00
rows=1 width=8)
Filter: ((typeid = 8) AND (core.sensorcoreid =
sensorcoreid))
-> Index Scan using ix_coredetail8 on coredetail8
cored_1 (cost=2.27..5.38 rows=1 width=8)
Index Cond: (sensorcoreid = core.sensorcoreid)
Filter: (typeid = 8)

--
-- Plan using child partition
--
EXPLAIN
SELECT core.sensorcoreid
FROM sensor.sensorcore8 core
JOIN sensor.coredetail cored ON cored.typeid = core.typeid AND
cored.sensorcoreid = core.sensorcoreid
JOIN sensor.corefilldetail corefd ON corefd.typeid = core.typeid AND
corefd.sensorcoreid = core.sensorcoreid
WHERE
core.typeid = 8 AND core.sensorid = 1814821;
QUERY PLAN

----------------------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=2.27..415.58 rows=38 width=4)
Join Filter: (core.sensorcoreid = cored.sensorcoreid)
-> Nested Loop (cost=2.27..227.03 rows=38 width=12)
-> Index Scan using ix_sensorcore8 on sensorcore8 core
(cost=2.27..54.20 rows=38 width=8)
Index Cond: (sensorid = 1814821)
Filter: (typeid = 8)
-> Append (cost=0.00..4.39 rows=2 width=8)
-> Seq Scan on corefilldetail corefd (cost=0.00..0.00
rows=1 width=8)
Filter: ((typeid = 8) AND (core.sensorcoreid =
sensorcoreid))
-> Index Only Scan using
corefilldetail8_typeid_sensorcoreid_idx on corefilldetail8 corefd_1
(cost=2.27..4.39 rows=1 width=8)
Index Cond: ((typeid = 8) AND (sensorcoreid =
core.sensorcoreid))
-> Append (cost=0.00..4.78 rows=2 width=8)
-> Seq Scan on coredetail cored (cost=0.00..0.00 rows=1
width=8)
Filter: ((typeid = 8) AND (corefd.sensorcoreid =
sensorcoreid))
-> Index Scan using ix_coredetail8 on coredetail8 cored_1
(cost=2.27..4.78 rows=1 width=8)
Index Cond: (sensorcoreid = corefd.sensorcoreid)
Filter: (typeid = 8)