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semijoin with empty right bat does not return immediately #6237

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monetdb-team opened this issue Nov 30, 2020 · 0 comments
Closed

semijoin with empty right bat does not return immediately #6237

monetdb-team opened this issue Nov 30, 2020 · 0 comments

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@monetdb-team monetdb-team commented Nov 30, 2020

Date: 2017-03-01 16:52:32 +0100
From: @swingbit
To: GDK devs <>
Version: 11.25.5 (Dec2016-SP1)

Last updated: 2017-03-31 13:28:43 +0200

Comment 25075

Date: 2017-03-01 16:52:32 +0100
From: @swingbit

User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36
Build Identifier:

The following trace line looked strange to me:

| 312749 | C_161=<tmp_2405>[0]:bat[:oid] := algebra.subinter(X_131=<tmp_2344>[30395024]:bat[:oid],X_160=<tmp_2407>[0]:bat[:oid],nil:BAT,nil:BAT,false:bit,nil:lng);

312 milliseconds for a no-op (right bat is empty)

Looking at the code, I have the impression that joininitresults does not handle this case properly, i.e. it returns a result size equal to the count of the left bat. Hence, it allocates a result bat for 30395024 tuples, for nothing.

I didn't check carefully whether the actual join also misses an early-exit condition.

Reproducible: Always

$ mserver5 --version
MonetDB 5 server v11.25.10 (64-bit, 128-bit integers)
This is an unreleased version
Copyright (c) 1993-July 2008 CWI
Copyright (c) August 2008-2017 MonetDB B.V., all rights reserved
Visit http://www.monetdb.org/ for further information
Found 15.6GiB available memory, 8 available cpu cores
Libraries:
libpcre: 8.40 2017-01-11 (compiled with 8.40)
openssl: OpenSSL 1.0.2j 26 Sep 2016 (compiled with OpenSSL 1.0.2j-fips 26 Sep 2016)
libxml2: 2.9.3 (compiled with 2.9.3)
Compiled by: roberto@photon.hq.spinque.com (x86_64-unknown-linux-gnu)
Compilation: gcc -g -Werror -Wall -Wextra -W -Werror-implicit-function-declaration -Wpointer-arith -Wdeclaration-after-statement -Wundef -Wformat=2 -Wno-format-nonliteral -Winit-self -Winvalid-pch -Wmissing-declarations -Wmissing-format-attribute -Wmissing-prototypes -Wold-style-definition -Wpacked -Wunknown-pragmas -Wvariadic-macros -fstack-protector-all -Wstack-protector -Wpacked-bitfield-compat -Wsync-nand -Wjump-misses-init -Wmissing-include-dirs -Wlogical-op -Wunreachable-code
Linking : /usr/bin/ld -m elf_x86_64

Comment 25076

Date: 2017-03-01 17:37:15 +0100
From: MonetDB Mercurial Repository <>

Changeset 310b7a4f966d made by Sjoerd Mullender sjoerd@acm.org in the MonetDB repo, refers to this bug.

For complete details, see http//devmonetdborg/hg/MonetDB?cmd=changeset;node=310b7a4f966d

Changeset description:

Better check to see whether join result is empty.

This fixes bug #6237.
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