BUG #15032: Segmentation fault when running a particular query

The following bug has been logged on the website:

Bug reference: 15032
Logged by: Guo Xiang Tan
Email address: gxtan1990(at)gmail(dot)com
PostgreSQL version: 10.1
Operating system: Ubuntu 14.04.4 LTS
Description:

## `SELECT version()`

`PostgreSQL 10.1 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu
5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609, 64-bit`

## Query that results in segmentation fault

```
UPDATE posts
SET avg_time = (x.gmean / 1000)
FROM (SELECT post_timings.topic_id,
post_timings.post_number,
round(exp(avg(CASE WHEN msecs > 0 THEN ln(msecs) ELSE 0 END)))
AS gmean
FROM post_timings
INNER JOIN posts AS p2
ON p2.post_number = post_timings.post_number
AND p2.topic_id = post_timings.topic_id
AND p2.user_id <> post_timings.user_id
GROUP BY post_timings.topic_id, post_timings.post_number) AS x
WHERE (x.topic_id = posts.topic_id
AND x.post_number = posts.post_number
AND (posts.avg_time <> (x.gmean / 1000)::int OR posts.avg_time IS
NULL));
```

## Error in PostgreSQL log file

```
[163]: [15-1] LOG: server process (PID 1983) was terminated by signal 11:
Segmentation fault
[163]: [16-1] DETAIL: Failed process was running: UPDATE posts
SET avg_time = (x.gmean / 1000)
FROM (SELECT post_timings.topic_id,
post_timings.post_number,
round(exp(avg(CASE WHEN msecs > 0 THEN ln(msecs) ELSE 0 END)))
AS gmean
FROM post_timings
INNER JOIN posts AS p2
ON p2.post_number = post_timings.post_number
AND p2.topic_id = post_timings.topic_id
AND p2.user_id <> post_timings.user_id
GROUP BY post_timings.topic_id, post_timings.post_number) AS x
WHERE (x.topic_id = posts.topic_id
AND x.post_number = posts.post_number
AND (posts.avg_time <> (x.gmean / 1000)::int OR posts.avg_time IS
NULL))
;
[163]: [17-1] LOG: terminating any other active server processes
[2003]: [4-1] WARNING: terminating connection because of crash of another
server process
[2003]: [5-1] DETAIL: The postmaster has commanded this server process to
roll back the current transaction and exit, because another server process
exited abnormally and possibly corrupted shared memory.
[2003]: [6-1] HINT: In a moment you should be able to reconnect to the
database and repeat your command.
[2015]: [4-1] WARNING: terminating connection because of crash of another
server process
[2015]: [5-1] DETAIL: The postmaster has commanded this server process to
roll back the current transaction and exit, because another server process
exited abnormally and possibly corrupted shared memory.
```

## pg_dump for relevant tables

```
--
-- PostgreSQL database dump
--

-- Dumped from database version 10.1
-- Dumped by pg_dump version 10.1

SET statement_timeout = 0;
SET lock_timeout = 0;
SET idle_in_transaction_session_timeout = 0;
SET client_encoding = 'UTF8';
SET standard_conforming_strings = on;
SET check_function_bodies = false;
SET client_min_messages = warning;
SET row_security = off;

SET search_path = public, pg_catalog;

SET default_tablespace = '';

SET default_with_oids = false;

--
-- Name: posts; Type: TABLE; Schema: public; Owner: -
--

CREATE TABLE posts (
id integer NOT NULL,
user_id integer,
topic_id integer NOT NULL,
post_number integer NOT NULL,
raw text NOT NULL,
cooked text NOT NULL,
created_at timestamp without time zone NOT NULL,
updated_at timestamp without time zone NOT NULL,
reply_to_post_number integer,
reply_count integer DEFAULT 0 NOT NULL,
quote_count integer DEFAULT 0 NOT NULL,
deleted_at timestamp without time zone,
off_topic_count integer DEFAULT 0 NOT NULL,
like_count integer DEFAULT 0 NOT NULL,
incoming_link_count integer DEFAULT 0 NOT NULL,
bookmark_count integer DEFAULT 0 NOT NULL,
avg_time integer,
score double precision,
reads integer DEFAULT 0 NOT NULL,
post_type integer DEFAULT 1 NOT NULL,
vote_count integer DEFAULT 0 NOT NULL,
sort_order integer,
last_editor_id integer,
hidden boolean DEFAULT false NOT NULL,
hidden_reason_id integer,
notify_moderators_count integer DEFAULT 0 NOT NULL,
spam_count integer DEFAULT 0 NOT NULL,
illegal_count integer DEFAULT 0 NOT NULL,
inappropriate_count integer DEFAULT 0 NOT NULL,
last_version_at timestamp without time zone NOT NULL,
user_deleted boolean DEFAULT false NOT NULL,
reply_to_user_id integer,
percent_rank double precision DEFAULT 1.0,
notify_user_count integer DEFAULT 0 NOT NULL,
like_score integer DEFAULT 0 NOT NULL,
deleted_by_id integer,
edit_reason character varying(255),
word_count integer,
version integer DEFAULT 1 NOT NULL,
cook_method integer DEFAULT 1 NOT NULL,
wiki boolean DEFAULT false NOT NULL,
baked_at timestamp without time zone,
baked_version integer,
hidden_at timestamp without time zone,
self_edits integer DEFAULT 0 NOT NULL,
reply_quoted boolean DEFAULT false NOT NULL,
via_email boolean DEFAULT false NOT NULL,
raw_email text,
public_version integer DEFAULT 1 NOT NULL,
action_code character varying(255),
image_url character varying
);

--
-- Name: TABLE posts; Type: COMMENT; Schema: public; Owner: -
--

COMMENT ON TABLE posts IS 'If you want to query public posts only, use the
badge_posts view.';

--
-- Name: COLUMN posts.post_number; Type: COMMENT; Schema: public; Owner: -
--

COMMENT ON COLUMN posts.post_number IS 'The position of this post in the
topic. The pair (topic_id, post_number) forms a natural key on the posts
table.';

--
-- Name: COLUMN posts.raw; Type: COMMENT; Schema: public; Owner: -
--

COMMENT ON COLUMN posts.raw IS 'The raw Markdown that the user entered into
the composer.';

--
-- Name: COLUMN posts.cooked; Type: COMMENT; Schema: public; Owner: -
--

COMMENT ON COLUMN posts.cooked IS 'The processed HTML that is presented in a
topic.';

--
-- Name: COLUMN posts.reply_to_post_number; Type: COMMENT; Schema: public;
Owner: -
--

COMMENT ON COLUMN posts.reply_to_post_number IS 'If this post is a reply to
another, this column is the post_number of the post it''s replying to. [FKEY
posts.topic_id, posts.post_number]';

--
-- Name: COLUMN posts.reply_quoted; Type: COMMENT; Schema: public; Owner:
-
--

COMMENT ON COLUMN posts.reply_quoted IS 'This column is true if the post
contains a quote-reply, which causes the in-reply-to indicator to be
absent.';

--
-- Name: topics; Type: TABLE; Schema: public; Owner: -
--

CREATE TABLE topics (
id integer NOT NULL,
title character varying(255) NOT NULL,
last_posted_at timestamp without time zone,
created_at timestamp without time zone NOT NULL,
updated_at timestamp without time zone NOT NULL,
views integer DEFAULT 0 NOT NULL,
posts_count integer DEFAULT 0 NOT NULL,
user_id integer,
last_post_user_id integer NOT NULL,
reply_count integer DEFAULT 0 NOT NULL,
featured_user1_id integer,
featured_user2_id integer,
featured_user3_id integer,
avg_time integer,
deleted_at timestamp without time zone,
highest_post_number integer DEFAULT 0 NOT NULL,
image_url character varying(255),
like_count integer DEFAULT 0 NOT NULL,
incoming_link_count integer DEFAULT 0 NOT NULL,
category_id integer,
visible boolean DEFAULT true NOT NULL,
moderator_posts_count integer DEFAULT 0 NOT NULL,
closed boolean DEFAULT false NOT NULL,
archived boolean DEFAULT false NOT NULL,
bumped_at timestamp without time zone NOT NULL,
has_summary boolean DEFAULT false NOT NULL,
vote_count integer DEFAULT 0 NOT NULL,
archetype character varying(255) DEFAULT 'regular'::character varying
NOT NULL,
featured_user4_id integer,
notify_moderators_count integer DEFAULT 0 NOT NULL,
spam_count integer DEFAULT 0 NOT NULL,
pinned_at timestamp without time zone,
score double precision,
percent_rank double precision DEFAULT 1.0 NOT NULL,
subtype character varying(255),
slug character varying(255),
deleted_by_id integer,
participant_count integer DEFAULT 1,
word_count integer,
excerpt character varying(1000),
pinned_globally boolean DEFAULT false NOT NULL,
pinned_until timestamp without time zone,
fancy_title character varying(400),
highest_staff_post_number integer DEFAULT 0 NOT NULL,
featured_link character varying,
CONSTRAINT has_category_id CHECK (((category_id IS NOT NULL) OR
((archetype)::text <> 'regular'::text))),
CONSTRAINT pm_has_no_category CHECK (((category_id IS NULL) OR
((archetype)::text <> 'private_message'::text)))
);

--
-- Name: TABLE topics; Type: COMMENT; Schema: public; Owner: -
--

COMMENT ON TABLE topics IS 'To query public topics only: SELECT ... FROM
topics t LEFT INNER JOIN categories c ON (t.category_id = c.id AND
c.read_restricted = false)';

--
-- Name: post_timings; Type: TABLE; Schema: public; Owner: -
--

CREATE TABLE post_timings (
topic_id integer NOT NULL,
post_number integer NOT NULL,
user_id integer NOT NULL,
msecs integer NOT NULL
);

--
-- Name: posts_id_seq; Type: SEQUENCE; Schema: public; Owner: -
--

CREATE SEQUENCE posts_id_seq
START WITH 1
INCREMENT BY 1
NO MINVALUE
NO MAXVALUE
CACHE 1;

--
-- Name: posts_id_seq; Type: SEQUENCE OWNED BY; Schema: public; Owner: -
--

ALTER SEQUENCE posts_id_seq OWNED BY posts.id;

--
-- Name: topics_id_seq; Type: SEQUENCE; Schema: public; Owner: -
--

CREATE SEQUENCE topics_id_seq
START WITH 1
INCREMENT BY 1
NO MINVALUE
NO MAXVALUE
CACHE 1;

--
-- Name: topics_id_seq; Type: SEQUENCE OWNED BY; Schema: public; Owner: -
--

ALTER SEQUENCE topics_id_seq OWNED BY topics.id;

--
-- Name: posts id; Type: DEFAULT; Schema: public; Owner: -
--

ALTER TABLE ONLY posts ALTER COLUMN id SET DEFAULT
nextval('posts_id_seq'::regclass);

--
-- Name: topics id; Type: DEFAULT; Schema: public; Owner: -
--

ALTER TABLE ONLY topics ALTER COLUMN id SET DEFAULT
nextval('topics_id_seq'::regclass);

--
-- Name: topics forum_threads_pkey; Type: CONSTRAINT; Schema: public; Owner:
-
--

ALTER TABLE ONLY topics
ADD CONSTRAINT forum_threads_pkey PRIMARY KEY (id);

--
-- Name: posts posts_pkey; Type: CONSTRAINT; Schema: public; Owner: -
--

ALTER TABLE ONLY posts
ADD CONSTRAINT posts_pkey PRIMARY KEY (id);

--
-- Name: idx_posts_created_at_topic_id; Type: INDEX; Schema: public; Owner:
-
--

CREATE INDEX idx_posts_created_at_topic_id ON posts USING btree (created_at,
topic_id) WHERE (deleted_at IS NULL);

--
-- Name: idx_posts_deleted_posts; Type: INDEX; Schema: public; Owner: -
--

CREATE INDEX idx_posts_deleted_posts ON posts USING btree (topic_id,
post_number) WHERE (deleted_at IS NOT NULL);

--
-- Name: idx_posts_user_id_deleted_at; Type: INDEX; Schema: public; Owner:
-
--

CREATE INDEX idx_posts_user_id_deleted_at ON posts USING btree (user_id)
WHERE (deleted_at IS NULL);

--
-- Name: idx_topics_front_page; Type: INDEX; Schema: public; Owner: -
--

CREATE INDEX idx_topics_front_page ON topics USING btree (deleted_at,
visible, archetype, category_id, id);

--
-- Name: idx_topics_user_id_deleted_at; Type: INDEX; Schema: public; Owner:
-
--

CREATE INDEX idx_topics_user_id_deleted_at ON topics USING btree (user_id)
WHERE (deleted_at IS NULL);

--
-- Name: idxtopicslug; Type: INDEX; Schema: public; Owner: -
--

CREATE INDEX idxtopicslug ON topics USING btree (slug) WHERE ((deleted_at IS
NULL) AND (slug IS NOT NULL));

--
-- Name: index_forum_threads_on_bumped_at; Type: INDEX; Schema: public;
Owner: -
--

CREATE INDEX index_forum_threads_on_bumped_at ON topics USING btree
(bumped_at DESC);

--
-- Name: index_post_timings_on_user_id; Type: INDEX; Schema: public; Owner:
-
--

CREATE INDEX index_post_timings_on_user_id ON post_timings USING btree
(user_id);

--
-- Name: index_posts_on_reply_to_post_number; Type: INDEX; Schema: public;
Owner: -
--

CREATE INDEX index_posts_on_reply_to_post_number ON posts USING btree
(reply_to_post_number);

--
-- Name: index_posts_on_topic_id_and_post_number; Type: INDEX; Schema:
public; Owner: -
--

CREATE UNIQUE INDEX index_posts_on_topic_id_and_post_number ON posts USING
btree (topic_id, post_number);

--
-- Name: index_posts_on_user_id_and_created_at; Type: INDEX; Schema: public;
Owner: -
--

CREATE INDEX index_posts_on_user_id_and_created_at ON posts USING btree
(user_id, created_at);

--
-- Name: index_topics_on_created_at_and_visible; Type: INDEX; Schema:
public; Owner: -
--

CREATE INDEX index_topics_on_created_at_and_visible ON topics USING btree
(created_at, visible) WHERE ((deleted_at IS NULL) AND ((archetype)::text <>
'private_message'::text));

--
-- Name: index_topics_on_id_and_deleted_at; Type: INDEX; Schema: public;
Owner: -
--

CREATE INDEX index_topics_on_id_and_deleted_at ON topics USING btree (id,
deleted_at);

--
-- Name: index_topics_on_lower_title; Type: INDEX; Schema: public; Owner:
-
--

CREATE INDEX index_topics_on_lower_title ON topics USING btree
(lower((title)::text));

--
-- Name: index_topics_on_pinned_at; Type: INDEX; Schema: public; Owner: -
--

CREATE INDEX index_topics_on_pinned_at ON topics USING btree (pinned_at)
WHERE (pinned_at IS NOT NULL);

--
-- Name: index_topics_on_pinned_globally; Type: INDEX; Schema: public;
Owner: -
--

CREATE INDEX index_topics_on_pinned_globally ON topics USING btree
(pinned_globally) WHERE pinned_globally;

--
-- Name: post_timings_summary; Type: INDEX; Schema: public; Owner: -
--

CREATE INDEX post_timings_summary ON post_timings USING btree (topic_id,
post_number);

--
-- Name: post_timings_unique; Type: INDEX; Schema: public; Owner: -
--

CREATE UNIQUE INDEX post_timings_unique ON post_timings USING btree
(topic_id, post_number, user_id);

--
-- PostgreSQL database dump complete
--
```

## Stack trace after following
https://wiki.edubuntu.org/DebuggingProgramCrash

```
Program received signal SIGSEGV, Segmentation fault.
index_markpos (scan=0x0) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/access/index/indexam.c:373
373 /build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/access/index/indexam.c:
No such file or directory.

(gdb) bt
#0 index_markpos (scan=0x0) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/access/index/indexam.c:373
#1 0x000055a812746c68 in ExecMergeJoin (pstate=0x55a8131bc778) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/nodeMergejoin.c:1188
#2 0x000055a81272cf3f in ExecProcNode (node=0x55a8131bc778) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/include/executor/executor.h:250
#3 EvalPlanQualNext (epqstate=epqstate(at)entry=0x55a81318c518) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/execMain.c:3005
#4 0x000055a81272d342 in EvalPlanQual (estate=estate(at)entry=0x55a81318c018,
epqstate=epqstate(at)entry=0x55a81318c518,
relation=relation(at)entry=0x7f4e4e25ab68, rti=1, lockmode=<optimized out>,
tid=tid(at)entry=0x7ffd54492330, priorXmax=8959603) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/execMain.c:2521
#5 0x000055a812747af7 in ExecUpdate (mtstate=mtstate(at)entry=0x55a81318c468,
tupleid=tupleid(at)entry=0x7ffd54492450, oldtuple=oldtuple(at)entry=0x0,
slot=<optimized out>, slot(at)entry=0x55a8131a2f08,
planSlot=planSlot(at)entry=0x55a81319db60,
epqstate=epqstate(at)entry=0x55a81318c518, estate=0x55a81318c018, canSetTag=1
'\001') at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/nodeModifyTable.c:1113
#6 0x000055a8127480c5 in ExecModifyTable (pstate=0x55a81318c468) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/nodeModifyTable.c:1770
#7 0x000055a81272a28b in ExecProcNode (node=0x55a81318c468) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/include/executor/executor.h:250
#8 ExecutePlan (execute_once=<optimized out>, dest=0x7f4e4e18d7a8,
direction=<optimized out>, numberTuples=0, sendTuples=<optimized out>,
operation=CMD_UPDATE, use_parallel_mode=<optimized out>,
planstate=0x55a81318c468, estate=0x55a81318c018) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/execMain.c:1722
#9 standard_ExecutorRun (queryDesc=0x55a813156838, direction=<optimized
out>, count=0, execute_once=<optimized out>) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/execMain.c:363
#10 0x000055a812864f05 in ProcessQuery (plan=<optimized out>,
sourceText=0x55a8130f3b08 "UPDATE posts\n", ' ' <repeats 24 times>, "SET
avg_time = (x.gmean / 1000)\n", ' ' <repeats 24 times>, "FROM (SELECT
post_timings.topic_id,\n", ' ' <repeats 37 times>,
"post_timings.post_number,\n "..., params=0x0, queryEnv=0x0,
dest=0x7f4e4e18d7a8, completionTag=0x7ffd544927f0 "") at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/tcop/pquery.c:161
#11 0x000055a81286515b in PortalRunMulti
(portal=portal(at)entry=0x55a81318a008, isTopLevel=isTopLevel(at)entry=1 '\001',
setHoldSnapshot=setHoldSnapshot(at)entry=0 '\000',
dest=dest(at)entry=0x7f4e4e18d7a8, altdest=altdest(at)entry=0x7f4e4e18d7a8,
completionTag=completionTag(at)entry=0x7ffd544927f0 "") at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/tcop/pquery.c:1286
#12 0x000055a812865e04 in PortalRun (portal=portal(at)entry=0x55a81318a008,
count=count(at)entry=9223372036854775807, isTopLevel=isTopLevel(at)entry=1 '\001',
run_once=run_once(at)entry=1 '\001', dest=dest(at)entry=0x7f4e4e18d7a8,
altdest=altdest(at)entry=0x7f4e4e18d7a8, completionTag=0x7ffd544927f0 "") at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/tcop/pquery.c:799
#13 0x000055a8128618dc in exec_simple_query (query_string=0x55a8130f3b08
"UPDATE posts\n", ' ' <repeats 24 times>, "SET avg_time = (x.gmean /
1000)\n", ' ' <repeats 24 times>, "FROM (SELECT post_timings.topic_id,\n", '
' <repeats 37 times>, "post_timings.post_number,\n "...) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/tcop/postgres.c:1099
#14 0x000055a812862df6 in PostgresMain (argc=<optimized out>,
argv=argv(at)entry=0x55a81309b738, dbname=0x55a813053b78
"boingboing_discourse", username=<optimized out>) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/tcop/postgres.c:4088
#15 0x000055a81259cfe9 in BackendRun (port=0x55a813092c70) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/postmaster/postmaster.c:4357
#16 BackendStartup (port=0x55a813092c70) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/postmaster/postmaster.c:4029
#17 ServerLoop () at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/postmaster/postmaster.c:1753
#18 0x000055a8127f236b in PostmasterMain (argc=3, argv=<optimized out>) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/postmaster/postmaster.c:1361
#19 0x000055a81259e3e5 in main (argc=3, argv=0x55a813051a90) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/main/main.c:228

(gdb) bt full
#0 index_markpos (scan=0x0) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/access/index/indexam.c:373
__func__ = "index_markpos"
#1 0x000055a812746c68 in ExecMergeJoin (pstate=0x55a8131bc778) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/nodeMergejoin.c:1188
node = 0x55a8131bc778
joinqual = 0x55a8131bcac8
otherqual = 0x0
qualResult = <optimized out>
compareResult = <optimized out>
innerPlan = 0x55a8131c8958
innerTupleSlot = <optimized out>
outerPlan = 0x55a8131bdd60
outerTupleSlot = <optimized out>
econtext = 0x55a8131bc888
doFillOuter = 0 '\000'
doFillInner = 0 '\000'
__func__ = "ExecMergeJoin"
#2 0x000055a81272cf3f in ExecProcNode (node=0x55a8131bc778) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/include/executor/executor.h:250
No locals.
#3 EvalPlanQualNext (epqstate=epqstate(at)entry=0x55a81318c518) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/execMain.c:3005
oldcontext = 0x55a813146198
#4 0x000055a81272d342 in EvalPlanQual (estate=estate(at)entry=0x55a81318c018,
epqstate=epqstate(at)entry=0x55a81318c518,
relation=relation(at)entry=0x7f4e4e25ab68, rti=1, lockmode=<optimized out>,
tid=tid(at)entry=0x7ffd54492330, priorXmax=8959603) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/execMain.c:2521
slot = <optimized out>
copyTuple = 0x7f4e4e167d68
#5 0x000055a812747af7 in ExecUpdate (mtstate=mtstate(at)entry=0x55a81318c468,
tupleid=tupleid(at)entry=0x7ffd54492450, oldtuple=oldtuple(at)entry=0x0,
slot=<optimized out>, slot(at)entry=0x55a8131a2f08,
planSlot=planSlot(at)entry=0x55a81319db60,
epqstate=epqstate(at)entry=0x55a81318c518, estate=0x55a81318c018, canSetTag=1
'\001') at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/nodeModifyTable.c:1113
epqslot = <optimized out>
lockmode = LockTupleNoKeyExclusive
tuple = <optimized out>
resultRelInfo = 0x55a81318c2b8
resultRelationDesc = 0x7f4e4e25ab68
result = <optimized out>
hufd = {ctid = {ip_blkid = {bi_hi = 2, bi_lo = 29090}, ip_posid =
7}, xmax = 8959603, cmax = 4294967295}
recheckIndexes = 0x0
__func__ = "ExecUpdate"
#6 0x000055a8127480c5 in ExecModifyTable (pstate=0x55a81318c468) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/nodeModifyTable.c:1770
node = 0x55a81318c468
estate = 0x55a81318c018
operation = CMD_UPDATE
saved_resultRelInfo = 0x0
resultRelInfo = 0x55a81318c2b8
subplanstate = 0x55a81318d238
junkfilter = 0x55a8131a50a8
slot = 0x55a8131a2f08
tupleid = 0x7ffd54492450
tuple_ctid = {ip_blkid = {bi_hi = 2, bi_lo = 29090}, ip_posid =
11}
oldtupdata = {t_len = 0, t_self = {ip_blkid = {bi_hi = 0, bi_lo =
0}, ip_posid = 26680}, t_tableOid = 21928, t_data = 0x55a81318c018}
oldtuple = 0x0
__func__ = "ExecModifyTable"
#7 0x000055a81272a28b in ExecProcNode (node=0x55a81318c468) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/include/executor/executor.h:250
No locals.
#8 ExecutePlan (execute_once=<optimized out>, dest=0x7f4e4e18d7a8,
direction=<optimized out>, numberTuples=0, sendTuples=<optimized out>,
operation=CMD_UPDATE, use_parallel_mode=<optimized out>,
planstate=0x55a81318c468, estate=0x55a81318c018) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/execMain.c:1722
slot = <optimized out>
current_tuple_count = 0
#9 standard_ExecutorRun (queryDesc=0x55a813156838, direction=<optimized
out>, count=0, execute_once=<optimized out>) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/executor/execMain.c:363
estate = 0x55a81318c018
operation = CMD_UPDATE
dest = 0x7f4e4e18d7a8
sendTuples = <optimized out>
__func__ = "standard_ExecutorRun"
#10 0x000055a812864f05 in ProcessQuery (plan=<optimized out>,
sourceText=0x55a8130f3b08 "UPDATE posts\n", ' ' <repeats 24 times>, "SET
avg_time = (x.gmean / 1000)\n", ' ' <repeats 24 times>, "FROM (SELECT
post_timings.topic_id,\n", ' ' <repeats 37 times>,
"post_timings.post_number,\n "..., params=0x0, queryEnv=0x0,
dest=0x7f4e4e18d7a8, completionTag=0x7ffd544927f0 "") at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/tcop/pquery.c:161
queryDesc = 0x55a813156838
#11 0x000055a81286515b in PortalRunMulti
(portal=portal(at)entry=0x55a81318a008, isTopLevel=isTopLevel(at)entry=1 '\001',
setHoldSnapshot=setHoldSnapshot(at)entry=0 '\000',
dest=dest(at)entry=0x7f4e4e18d7a8, altdest=altdest(at)entry=0x7f4e4e18d7a8,
completionTag=completionTag(at)entry=0x7ffd544927f0 "") at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/tcop/pquery.c:1286
pstmt = 0x7f4e4e18d6c8
active_snapshot_set = 1 '\001'
stmtlist_item = 0x7f4e4e18d758
#12 0x000055a812865e04 in PortalRun (portal=portal(at)entry=0x55a81318a008,
count=count(at)entry=9223372036854775807, isTopLevel=isTopLevel(at)entry=1 '\001',
run_once=run_once(at)entry=1 '\001', dest=dest(at)entry=0x7f4e4e18d7a8,
altdest=altdest(at)entry=0x7f4e4e18d7a8, completionTag=0x7ffd544927f0 "") at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/tcop/pquery.c:799
save_exception_stack = 0x7ffd54492a20
save_context_stack = 0x0
local_sigjmp_buf = {{__jmpbuf = {1, -2410647209184299319,
94180362802640, 140726017533936, 94180363247624, 94180362802688,
-2410647209169619255, -8493467030827796791}, __mask_was_saved = 0,
__saved_mask = {__val = {8192, 0, 0, 12099560782854432544, 0,
94180356443286, 64, 140726017533776, 94180363247624, 88, 94180362802640, 2,
139974294427512, 140726017533808, 94180354932849, 2}}}}
result = <optimized out>
nprocessed = <optimized out>
saveTopTransactionResourceOwner = 0x55a8130a1938
saveTopTransactionContext = 0x55a8130a1bd8
saveActivePortal = 0x0
saveResourceOwner = 0x55a8130a1938
savePortalContext = 0x0
saveMemoryContext = 0x55a8130a1bd8
__func__ = "PortalRun"
#13 0x000055a8128618dc in exec_simple_query (query_string=0x55a8130f3b08
"UPDATE posts\n", ' ' <repeats 24 times>, "SET avg_time = (x.gmean /
1000)\n", ' ' <repeats 24 times>, "FROM (SELECT post_timings.topic_id,\n", '
' <repeats 37 times>, "post_timings.post_number,\n "...) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/tcop/postgres.c:1099
parsetree = 0x55a81311d5d0
portal = 0x55a81318a008
snapshot_set = <optimized out>
commandTag = <optimized out>
completionTag =
"\000(IT\375\177\000\000\001u\230\022\250U\000\000\060(IT\375\177\000\000(\022\346\022\001\000\000\000\234$\336\022\250U\000\000\234$\336\022\250U\000\000\b;\017\023\250U\000\000\001\000\000\000\000\000\000"
querytree_list = <optimized out>
plantree_list = <optimized out>
receiver = 0x7f4e4e18d7a8
format = 0
dest = DestRemote
parsetree_list = 0x55a81311d620
parsetree_item = 0x55a81311d600
save_log_statement_stats = 0 '\000'
was_logged = 0 '\000'
isTopLevel = 1 '\001'
msec_str =
"\000(IT\375\177\000\000\001u\230\022\250U\000\000\060(IT\375\177\000\000(\022\346\022\001\000\000"
__func__ = "exec_simple_query"
#14 0x000055a812862df6 in PostgresMain (argc=<optimized out>,
argv=argv(at)entry=0x55a81309b738, dbname=0x55a813053b78
"boingboing_discourse", username=<optimized out>) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/tcop/postgres.c:4088
query_string = 0x55a8130f3b08 "UPDATE posts\n", ' ' <repeats 24
times>, "SET avg_time = (x.gmean / 1000)\n", ' ' <repeats 24 times>, "FROM
(SELECT post_timings.topic_id,\n", ' ' <repeats 37 times>,
"post_timings.post_number,\n "...
firstchar = 81
input_message = {data = 0x55a8130f3b08 "UPDATE posts\n", ' '
<repeats 24 times>, "SET avg_time = (x.gmean / 1000)\n", ' ' <repeats 24
times>, "FROM (SELECT post_timings.topic_id,\n", ' ' <repeats 37 times>,
"post_timings.post_number,\n "..., len = 942, maxlen = 1024, cursor =
942}
local_sigjmp_buf = {{__jmpbuf = {140726017534400,
-2410647209056373047, 94180362270520, 1, 94180362270200, 94180362234992,
-2410647208949418295, -8493467028741261623}, __mask_was_saved = 1,
__saved_mask = {__val = {0, 140726017534704, 94180352583639, 94180359415580,
140726017534620, 94180359731456, 94180356159802, 140726017534928, 686, 0,
94180359927584, 94180362234992, 139974255290296, 94180359464352,
206158430256, 140726017534912}}}}
send_ready_for_query = 0 '\000'
disable_idle_in_transaction_timeout = <optimized out>
__func__ = "PostgresMain"
#15 0x000055a81259cfe9 in BackendRun (port=0x55a813092c70) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/postmaster/postmaster.c:4357
ac = 1
secs = 570264982
usecs = 174473
i = 1
av = 0x55a81309b738
maxac = <optimized out>
#16 BackendStartup (port=0x55a813092c70) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/postmaster/postmaster.c:4029
bn = <optimized out>
pid = <optimized out>
#17 ServerLoop () at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/postmaster/postmaster.c:1753
rmask = {fds_bits = {64, 0 <repeats 15 times>}}
selres = <optimized out>
now = <optimized out>
readmask = {fds_bits = {112, 0 <repeats 15 times>}}
last_lockfile_recheck_time = 1516949750
last_touch_time = 1516949630
__func__ = "ServerLoop"
#18 0x000055a8127f236b in PostmasterMain (argc=3, argv=<optimized out>) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/postmaster/postmaster.c:1361
opt = <optimized out>
status = <optimized out>
userDoption = <optimized out>
listen_addr_saved = 1 '\001'
i = <optimized out>
output_config_variable = <optimized out>
__func__ = "PostmasterMain"
#19 0x000055a81259e3e5 in main (argc=3, argv=0x55a813051a90) at
/build/postgresql-10-qAeTPy/postgresql-10-10.1/build/../src/backend/main/main.c:228
No locals.
```

## Configuration changes

```
shared_buffers = "1GB"
work_mem = "16MB"
maintenance_work_mem = "16MB"
```

Do feel free to let me know if I'm required to provide more information and
I'll be happy to do so.