Hello Michael,

From my experience, all "write" request executed concurrently always end with concurrency conflict. I'm talking of heavey request during several minutes, so it's easy to get concurrent access. Since i only use monetdb with a single process, stability was greatly improved.

Regards Guillaume BASSOT Web Developer +33 (0)1 55 48 02 82 gbassot@inbox.fr 30, rue Vincent Moris 92240 Malakoff - France Fax : +33 (0)1 55 48 02 79 2015-06-30 10:09 GMT+02:00 :

Hi all,

It’s a pity that no one answered the question I asked a few weeks ago about crashes of MonetDB 5 server under windows 64 Bit.

So I think I offer more information about a scenario where the databases crashes. Hopefully someone could give me a hint how to improve stability of MonetDB under Windows 64 Bit with concurrent client connections.

We are using Monet DB for a couple of months and facing some graved issues with concurrent queries.

The problem is, when we query the database with two or more clients in a parallel, the database crashes!

These are the facts:

MonetDB server version: v11.19.9

================================

# MonetDB 5 server v11.19.9 "Oct2014-SP2"

# Serving database 'uniserv', using 2 threads

# Compiled for x86_64-pc-winnt/64bit with 64bit OIDs dynamically linked

# Found 8.000 GiB available main-memory.

# Copyright (c) 1993-July 2008 CWI.

# Copyright (c) August 2008-2015 MonetDB B.V., all rights reserved

# Visit http://www.monetdb.org/ for further information

# Listening for connection requests on mapi:monetdb://QADQSHWIN:50000/

# MonetDB/SQL module loaded

Server crashes also occur on versions v11.19.8 and v11.19.7.

Operation system:

=================

Microsoft Windows Server 2008 R2 Datacenter

Version 6.1.7601 Service Pack 1 Build 7601

hosted on VMWare Virtual Platform

x64-based PC

2x Processor Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz, 2800 Mhz, 1 Core(s), 1 Logical Processor(s)

Installed Physical Memory (RAM) 8,00 GB

Available Physical Memory 5,25 GB

Total Virtual Memory 16,0 GB

Server installation folder:

===========================

E:\Program Files\MonetDB\MonetDB5

Server startup script M5server.bat:

===================================

@REM Copyright August 2008-2014 MonetDB B.V.

@REM All Rights Reserved.

@echo off

setlocal

rem figure out the folder name

set MONETDB=%~dp0

rem remove the final backslash from the path

set MONETDB=%MONETDB:~0,-1%

rem extend the search path with our EXE and DLL folders

set PATH=%MONETDB%\bin;%MONETDB%\lib;%MONETDB%\lib\MonetDB5;%PATH%

rem prepare the arguments to mserver5 to tell it where to put the dbfarm

REM Uniserv: Don't use APPDATA, so set APPDATA to empty String.

set APPDATA=

if "%APPDATA%" == "" goto usevar

rem if the APPDATA variable does exist, put the database there

set MONETDBDIR=%APPDATA%\MonetDB5

set MONETDBFARM="--dbpath=%MONETDBDIR%\dbfarm\demo"

goto skipusevar

:usevar

rem if the APPDATA variable does not exist, put the database in the

rem installation folder (i.e. default location, so no command line argument)

REM Uniserv: Specify the DB installation folder

rem set MONETDBDIR=%MONETDB%\var\MonetDB5

set MONETDBDIR=%MONETDB%\db

set MONETDBFARM="--dbpath=%MONETDBDIR%\dbfarm\uniserv"

:skipusevar

rem the SQL log directory used to be in %MONETDBDIR%, but we now

rem prefer it inside the dbfarm, so move it there

if not exist "%MONETDBDIR%\sql_logs" goto skipmove

for /d %%i in ("%MONETDBDIR%"\sql_logs\*) do move "%%i" "%MONETDBDIR%\dbfarm"\%%~ni\sql_logs

rmdir "%MONETDBDIR%\sql_logs"

:skipmove

rem start the real server

"%MONETDB%\bin\mserver5.exe" --set "prefix=%MONETDB%" --set mapi_open=true --set mapi_port=50000 --set max_clients=1000 --set "exec_prefix=%MONETDB%" %MONETDBFARM% %*

if ERRORLEVEL 1 pause

endlocal

MonetDB JDBC Client:

================

We query the database via the latest MonetDB JDBC driver loaded from the central Maven repository:

<groupId>monetdb</groupId>

<artifactId>monetdb-jdbc</artifactId>

<version>2.14</version>

Database tables:

================

We create tables called "rule_result_<n>"

CREATE TABLE "dq_scorecard"."rule_results_1" ("id" BIGINT NOT NULL PRIMARY KEY AUTO_INCREMENT, "record_id" VARCHAR(1024), "rule_1" INT, "rule_2" INT, ...);

Each table has about 50+ INT columns.

Query scenarios:

================

We have concurrent read access via JDBC driver and Spring Data Access Objects,

the query look like that:

*Client 1: 50 aggregate queries on 50 different columns on one database table like that:

SELECT AVG("rule_n") FROM "dq_scorecard"."rule_results_1" WHERE "rule_n"

...

= 0

*Client 2: 50 aggregate queries on 50 different columns on another database table like that:

SELECT AVG("rule_n") FROM "dq_scorecard"."rule_results_2" WHERE "rule_n"

...

= 0

*Client 3: 50 aggregate queries on 50 different columns on another database table like that:

SELECT AVG("rule_n") FROM "dq_scorecard"."rule_results_3" WHERE "rule_n"

...

= 0

All clients run concurrently, at the moment we don't use a connection pool and create a connection for every query.

During concurrent access the M5server crashes.

The server crashes when each table has 100 records! Our production tables can have up to 50. 000. 000 of records!

Kind regards,

Michael

*From:* users-list [mailto:users-list-bounces+michael.witt= uniserv.com@monetdb.org] *On Behalf Of *michael.witt@uniserv.com *Sent:* Donnerstag, 28. Mai 2015 14:32 *To:* users-list@monetdb.org *Subject:* Concurrency test causes crash of MonetDB 5 server

Hi,

we experience a crash of MonetDB 5 server during tests of a multi-threaded client access via JDBC-Driver and MapiSocket:

The application is already optimized to avoid “concurrency conflicts” because of the “Optimistic Concurrency Control” concept.

The test simulates client access via two threads.

All update operations (INSERT, UPDATE, DELETE, DROP TABLE, CREATE TABLE) are done in serial.

All read operations are done in parallel to other read operations or to update operations.

The test causes a crash of mserver5.exe after a few minutes.

If the test uses just one thread, all read and update operations are done in serial and the server does not crash.

What is the rule of thumb to avoid crashes when using several client threads?

*Crash details:*

*Problem signature:*

Problem Event Name: APPCRASH

Application Name: mserver5.exe

Application Version: 0.0.0.0

Application Timestamp: 55389f58

Fault Module Name: StackHash_8ec6

Fault Module Version: 6.1.7601.18247

Fault Module Timestamp: 521eaf24

Exception Code: c0000374

Exception Offset: 00000000000c4102

OS Version: 6.1.7601.2.1.0.144.8

Locale ID: 1031

Additional Information 1: 8ec6

Additional Information 2: 8ec62499039d1d8234b025a62c725eb7

Additional Information 3: f8f3

Additional Information 4: f8f3e520847c0684b15d4080171779ef

# MonetDB 5 server v11.19.9 "Oct2014-SP2"

# Serving database 'uniserv', using 4 threads

# Compiled for x86_64-pc-winnt/64bit with 64bit OIDs dynamically linked

# Found 10.000 GiB available main-memory.

..

# MonetDB/SQL module loaded

Michael Witt

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