Sizing and tuning guide for Rational DOORS Next Generation 6.0.4 (DRAFT)

Authors: Mahesh Gunbote, Lee Byrnes
Build basis: DNG 6.0.4 ifix 6.

Introduction

The 6.0.4 ifix 6 release of IBM® Rational® DOORS® Next Generation (RDNG) introduced several changes to the performance of the overall product architecture and the purpose this is an update the sizing guides for that release.

This 6.0.4 sizing guide focuses on the improvement of the scalability of a deployment (where scalability refers to the maximum throughput/user load which can be achieved for a given repository size without significant response degradation) and it's overall response times.

Standard Disclaimer

The information in this document is distributed AS IS. The use of this information or the implementation of any of these techniques is a customer responsibility and depends on the customer's ability to evaluate and integrate them into the customer's operational environment. While each item may have been reviewed by IBM for accuracy in a specific situation, there is no guarantee that the same or similar results will be obtained elsewhere. Customers attempting to adapt these techniques to their own environments do so at their own risk. Any pointers in this publication to external Web sites are provided for convenience only and do not in any manner serve as an endorsement of these Web sites. Any performance data contained in this document was determined in a controlled environment, and therefore, the results that may be obtained in other operating environments may vary significantly. Users of this document should verify the applicable data for their specific environment.

Performance is based on measurements and projections using standard IBM benchmarks in a controlled environment. The actual throughput or performance that any user will experience will vary depending upon many factors, including considerations such as the number of other applications running in the customer environment, the I/O configuration, the storage configuration, and the workload processed. Therefore, no assurance can be given that an individual user will achieve results similar to those stated here.

This testing was done as a way to compare and characterize the differences in performance between different configurations of the 6.0 product. The results shown here should thus be looked at as a comparison of the contrasting performance between different configurations, and not as an absolute benchmark of performance.

How hardware configurations impact scalability

We conducted a series of tests with different hardware configurations, to assess the impact of memory and disk drives on scalability. These tests cover the same configurations as in the 6.0 sizing guide, with the exception of the SSD tests which are no longer part of the test sequence. We carried out these tests by setting up a specific hardware configuration and repository size, and then slowly increasing the number of simulated users until we started to see increasing response times or we reached the recommeded supported number of users (500).

As a general rule, the system can support more users (and more artifacts) as the amount of RAM on the DNG server increases. The DNG server stores all the data in use in indices local to the RM server and will cache this index in memory if possible, which is why increasing the amount of RAM can improve performance. The amount of RAM available to cache the DNG index is roughly the total amount of RAM minus the maximum size of the JVM heap. If the disk size of the DNG index (in server/conf/rm/indices) is less than that number, then the DNG index will be cached in memory, which will allow for the fastest read access to DNG data. The DNG index will be accessed from the file system when there isn't enough memory to cache the index completely (but also on write operations).

A note on failure modes

What we see in all cases is that the response times slowly increase as the user load increases up to a point - and at that point, there is a sudden, sharp increase in response times. At the same time, the CPU utilization on the DNG server increases to 100%. This is the classic symptom of lock contention in Java. As the load increases, the simulated users start to ask for exclusive access to the same data, and this causes a queue to form. The bottleneck forms around access to the DNG index information. We have observed that the user load at which this happens is not consistent, and so there is a margin of error on the user estimates of +/- 50-100 users.

This failure mode is in part a consequence of the performance simulation itself, which issues a stream of requests against the server at a steady rate, without pause. Our simulated users never take breaks for coffee, or go to meetings, or go to lunch! This represents a worst case scenario, where the server can never catch up. In production usage, it would be common for bursts of operations to be followed by slow periods, during which the server can catch up.

Tuning recommendations for all configurations

JVM nursery sizing: 1/3 of max JVM heap

When allocating memory for the Java Virtual machine for the DNG server, allocate 1/3 of the total heap to the nursery (divide the value of -Xmx by 3, and use that for -Xmn).

The nursery is a section of JVM memory used to efficiently manage short-lived objects, such as those associated with handling an incoming HTTP request. As the number of concurrent DNG users grows, there is more demand on the nursery to process the incoming transactions. If the nursery is too small, memory for those objects will be copied into sections of JVM memory which have more management overhead. By allocating more memory to the nursery, you can improve performance at higher load levels by ensuring that short-lived objects stay in the nursery.

Tuning the configuration management cache

Some information about streams and baselines is cached in memory. The cache size can be changed to improve the performance for higher user loads (with the tradeoff being additional memory usage). You control the cache settings through JVM startup parameters (e.g. through the -D flag or by using custom JVM properties).

The cache stores information which DNG associates with each configuration (where a configuration is a stream, baseline, or change set). For best performance, set the cache size to the number of concurrent users. This supports the worst-case scenario where all active users are working in separate configurations. The default value for this cache is 200.

To set as a JVM startup parameter:

-Dcom.ibm.rdm.configcache.size=400

Assume that each active entry in the cache will consume 2M of RAM.

For additional tuning guidance for the configuration cache, refer to this technote Tuning the configuration cache for IBM Rational DOORS Next Generation

Keeping database statistics up-to-date

Information about streams, baselines, and changesets is stored in tables in the database. The DNG server will query these tables when users work in a DNG project which is enabled for configuration management. For best performance, be sure that the database statistics are kept up to date as the size of the repository grows. This is especially critical when you are first adopting configuration management. Some of the tables will start out empty, and then grow as users work with streams, baselines, and change sets. Keeping the database statistics updated ensures that the queries against those tables will be properly optimized.

Databases generally manage statistics automatically; for example, in a scheduled overnight operation. However, to ensure that the database is fully optimized, you can manually run the statistics as follows. DB2

DB2 REORGCHK UPDATE STATISTICS ON TABLE ALL 

Oracle

EXEC DBMS_STATS.GATHER_DATABASE_STATS

See also Slow server performance and CRRRW7556E on IBM Rational DOORS Next Generation version 6.0.x for further information on keeping databases tuned for configuration management, if you are experiencing performance issues.

Available TCP/IP ports

The default number of TCP/IP ports that are available on AIX and Linux operating systems is too low and must be increased. Windows operating systems have a higher default limit, but that limit might still be too low for large concurrent user loads. Use the following instructions to increase the port range.

• On AIX and Linux systems, set the limit as follows: ulimit -n 65000
• On Windows 2003 Server, follow these steps:
  • Open the registry.
  • Navigate to HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/Tcpip/Parameters and create a dWord named MaxUserPort. Set its value to 65000.
  • Restart the computer.
• On Windows 2008 Server, follow the instructions in this Microsoft support article to change the dynamic port range. For the start port setting, use 2000. Set the number of ports to 63535.

Thread pool size

The WebSphere Application Server thread pool size must be increased from the default of 50 to 0.75 times the expected user load. For example, if you have 400 concurrent users, the thread pool maximum should be set to 300.

More suggestions

In a 3-server topology, where Jazz Team Server and the DNG server are on separate hardware, adjust two settings in the fronting.properties file for loads higher than 200 concurrent users.

• Ensure that com.ibm.rdm.fronting.server.connection.route.max equals the number of users
• Ensure that com.ibm.rdm.fronting.server.connection.max is twice the value of number of users

When you use a proxy or reverse proxy server, you might need to increase the maximum allowed connections on the proxy server, depending on the concurrent user load. For more information, see Tuning IBM HTTP Server to maximize the number of client connections to WebSphere Application Server .

Repositories with up to 500,000 artifacts

The chart below summarizes the results of testing with a repository of 500,000 artifacts, using a standard configuration management workload. Here we looked at the impact of the amount of RAM on the response times and maximum user limit. The system with 32G RAM performed the worst. Given that the 500K repository has a 34G index in DNG 6.0.2, and our 32G system has only 16G or less available for caching, this is not unexpected. Increasing the amount of RAM to 64G allows for most of the index to be cached in memory. Performance for both the 64G and 128G systems are better than the 32GB system and there is a notable improvement in user number support when compared to DNG 6.0.

The maximum user load for the 64G system was again higher than the 128Gb system (700 users vs. 600 for 128G). This is related to the inconsistencies discussed earlier regarding the exact point at which bottleneck around the DNG index forms. We therefore use 600 users as the limit for the 500,000 artifacts, to be conservative.

IMAGE FOR 500 GOES HERE

The following table shows the various hardware configurations with RAM and heap sizes and the maximum number of concurrent users that are supported in each hardware configuration for the DNG 6.0.2 and DNG 6.0.4 releases. Again this is related to the inconsistencies discussed earlier regarding the exact point at which bottleneck around the DNG index forms.

RM server hardware and JVM configuration	Jazz Team Server	DB2 server	Number of users supported in DNG 6.0.2	Number of users supported in DNG 6.0.4	Change in user numbers
32 GB RAM with 16 GB JVM heap	32 GB RAM with 16 GB JVM heap	64 GB RAM	500	500	-0
64 GB RAM with 24 GB JVM heap	32 GB RAM with 16 GB JVM heap	64 GB RAM	500	500	0
128 GB RAM with 24 GB JVM heap	32 GB RAM with 16 GB JVM heap	64 GB RAM	500	500	0

Repositories with up to 1M artifacts

The chart below shows response times as a function of user load for a repository with 1 million artifacts, for a variety of hardware configurations. Here are the main observations:

• More than 32G of RAM is needed to cache the index (68G) associated with 1M artifacts, so the response times and scale limits are lowest in 32G configurations.

IMAGE FOR 1000 GOES HERE
Image for 1000 less 32Gb

The following table shows the various hardware configurations with RAM, heap sizes and the maximum number of concurrent users that are supported in each hardware configuration for the DNG 6.0.2 and DNG 6.0.4 releases. Again this is related to the inconsistencies discussed earlier regarding the exact point at which bottleneck around the DNG index forms.

RM server hardware and JVM configuration	Jazz Team Server	DB2 server	Number of users supported in DNG 6.0	Number of users supported in DNG 6.0.2	Change in user numbers
HDD – 32 GB RAM with 16 GB JVM heap	32 GB RAM with 16 GB JVM heap	64 GB RAM	400	100	-300
HDD – 64 GB RAM with 24 GB JVM heap	32 GB RAM with 16 GB JVM heap	64 GB RAM	500	500	0
HDD – 128 GB RAM with 24 GB JVM heap	32 GB RAM with 16 GB JVM heap	64 GB RAM	500	500	0

Appendix A: Topology

The topology that was used in our testing is based on the standard (E1) Enterprise - Distributed / Linux / DB2 topology

TEST TOPOLOGY GRAPH HERE

Key:

• RM Server: Rational DOORS Next Generation Server
• JTS: Jazz™ Team Server

The performance tests described here did not include linking scenarios, and so the back link indexer and the global configuration application were not deployed into our test environment.

Appendix B: Tested hardware and software configurations

All of the hardware that was tested was 64 bit and supported hyperthreading. The following table shows the server hardware configurations that were used for all of the tests of all repository sizes.

Function	Number of machines	Machine type	Processor/machine	Total processor cores/machines	Memory/machine		Network interface	OS and version
Proxy Server (IBM HTTP Server and WebSphere Plugin)	1	IBM System x3250 M4	1 x Intel Xeon E3-1240v2 3.4 GHz (quad-core)	8	16 GB	Gigabit Ethernet		Red Hat Enterprise Linux Server release 6.3 (Santiago)
Jazz Team Server WebSphere Application Server 8.5.5.1	1	IBM System x3550 M4	2 x Intel Xeon E5-2640 2.5 GHz (six-core)	24	32 GB	Gigabit Ethernet		Red Hat Enterprise Linux Server release 6.3 (Santiago)
RM server WebSphere Application Server 8.5.5.1	1	IBM System x3550 M4	2 x Intel Xeon E5-2640 2.5 GHz (six-core)	24	Varied, depending on the repository size and hard disk type. 32 GB to 128 GB	Gigabit Ethernet		Red Hat Enterprise Linux Server release 6.3 (Santiago)
Database server DB2 10.1.2	1	IBM System x3650 M4	2 x Intel Xeon E5-2640 2.5 GHz (six-core)	24	64 GB	Gigabit Ethernet		Red Hat Enterprise Linux Server release 6.3 (Santiago)
Network switches	N/A	Cisco 2960G-24TC-L	N/A	N/A		Gigabit Ethernet		24 Ethernet 10/100/1000 ports

Appendix C: Test data shape and volume

The test data that was used for these sizing guide tests represents extremely large repositories compared to most environments that are currently deployed. The 6.0 tests used repositories containing 500K and 1 million artifacts. The artifacts, modules, comments, links, and other elements were evenly distributed among the projects. Each project had data as shown in the following table.

Artifact type	Number
Large modules (10,000 artifacts)	2
Medium modules (1500 artifacts)	40
Small modules (500 artifacts)	10
Folders	119
Module artifacts	85000
Non-module artifacts	1181
Comments	260582
Links	304029
Collections	14
Public tags	300
Private tags	50
Views	200
Terms	238
Streams	15
Baselines	15
Change sets	600

Each repository that was tested contained a different number of projects. In each project, the data was distributed as shown in the previous table. The categories of RM artifacts in the repository were evenly distributed among all of the available projects in the repositories.

Artifact type	500,000-artifact repository	1-million-artifact repository	2-million-artifact repository
Projects	6	12	24
Large modules (10,000 artifacts)	12	24	48
Medium modules (1500 artifacts)	240	480	960
Small modules (500 artifacts)	60	120	240
Folders	714	1428	2856
Module artifacts	510,000	1,020,000	2,040,000
Non-module artifacts	7086	14,172	28344
Comments	1,563,492	3,126,984	6,253,968
Links	1,824,174	3,648,348	7,296,696
Collections	84	168	336
Public tags	1800	3600	7200
Private tags	300	600	1200
Views	1200	2400	4800
Terms	1428	2856	5712
Streams	90	180	360
Baselines	90	180	360
Change sets	600	1200	3600
Index size on disk	39 GB	75 GB	157 GB

Appendix D: Workload characterization

IBM® Rational® Performance Tester was used to simulate the workload. A Rational Performance Tester script was created for each use case. The scripts are organized by pages; each page represents a user action. Users were distributed into many user groups and each user group repeatedly runs one script (use case). The RM team used the user load stages in Rational Performance Tester to capture the performance for various user loads.

We started with 100 simulated users, and increased the load by 100 users every 90 minutes. After the 400 user stage, we increased the user load in increments of 50 up until failure.

In each stage, the users set up in 15 minutes. After they log in, they are allowed another 15 minutes to get settled. Then, tests are iterated for 45 minutes. During that time, tests were run with a 1 minute “think time” between operations for each user.

This table shows the use cases and the number of users who were repeatedly running each script. Change sets are created in the default stream.

Use case	Description	Number of users
Edit stream	Select the default configuration. Navigate to the streams, baselines, and change set tabs..	2%
Create stream/baseline	Create a stream and a baseline as children of the default stream. Runs 5 times per hour per user.	1%
Select random baseline	Open the Switch configuration UI; select a random baseline and switch to it.	1%
Select random stream	Open the Switch configuration UI; select a random stream and switch to it.	1%
Copy/Paste/Move/Delete	Create a change set. Open a module that contains 1500 artifacts, select 25 artifacts, move them by using the copy and paste functions, and then delete the copied artifacts. Deliver the change set.	1%
Create an artifact	Create a change set. Create non-module artifacts. Deliver the change set.	3%
Create a collection	Create a change set. Create collections that contain 10 artifacts. Deliver the change set.	4%
Create a module artifact end-to-end scenario	Create a change set. Open a medium module that contains 1500 artifacts, create a module artifact, edit the new artifact, and delete the new artifact. Deliver the change set 75% of the time; discard the change set 25% of the time.	12%
Create a small module artifact end-to-end scenario	create a change set. Open a small module that contains 500 artifacts, create a module artifact, edit that new artifact, and delete the new artifact. Deliver the change set 50% of the time; discard the change set 50% of the time.	6%
Create a comment in a module artifact	Create a change set. Open a medium module that contains 1500 artifacts, open an artifact that is in the module, expand the Comments section of the artifact, and create a comment. Deliver the change set 83% of the time; discard the change set 17% of the time.	18%
Hover over a module artifact and edit it	Create a change set. Open a module that contains 1500 artifacts and hover over an artifact. When the rich hover is displayed, edit the artifact text. Deliver the change set.	2%
Hover over and open a collection	Display all of the collections, hover over a collection, and then open it.	1%
Manage folders	Click “Show Artifacts” to display folder tree and then create a folder. Move the new folder into another folder and then delete the folder that you just created.	1%
Open the project dashboard	Open a dashboard that displays the default dashboard.	5%
Search by ID and string	Open a project, select a folder, search for an artifact by its numeric ID, and click a search result to display an artifact. Search for artifacts by using a generic string search that produces about 50 results.	9%
Scroll 20 pages in a module	Open a module that contains 1500 artifacts and then scroll through 20 pages.	16%
Switch the module view	Open a module that contains 1500 artifacts and then change the view to add columns that display user-defined attributes.	14%
Upload a 4 MB file as a new artifact	Upload a file and create an artifact.	4%

Throughput of tests

As explained in the workload characterization, the test load was aggressive and it simulated the load of very active users. After the users were logged in, they continuously ran the scripts, waiting for only 1 minute before running each page. During the tests, transaction throughput statistics were gathered. Those statistics were the basis for the high-level overview of server activity that is shown in the next table.

Server activity	100 users in 1 hour	100 users in 8 hours	400 users in 8 hours
Number of artifacts created	369	2952	11808
Number of artifacts opened	280	2240	8960
Number of artifacts edited or deleted	308	2464	9856
Display a list of modules	591	4728	18912
Comments created	162	1296	5184
Modules opened	588	4704	18816
Search by ID and open the artifact	133	1064	4256
Search by string	132	1056	4224
Switch module view to filter by attribute	270	2160	8640
Number of module pages scrolled	834	6672	26688
Create stream	8	64	256
Create baseline	8	64	256
Switch to a stream	104	832	3328
Switch to a baseline	80	640	2560
Browse the current configuration	101	808	3232
Create change set	360	2880	11520
Discard change set	68	544	2176
Deliverchange set	290	2320	9280

Appendix E: Server tuning

JVM heap and GC tuning

In general, the team used 50% of the available RAM as the JVM heap size and did not exceed the maximum heap size of 24 GB. Because the Jazz Team Server had 32 GB of RAM, the team used 16 GB for the maximum heap size. The JVM arguments that the team used to set the JVM heap sizes and the GC policy are as follows:

 -Xgcpolicy:gencon –Xmx16g –Xms16g –Xmn4G -Xcompressedrefs -Xgc:preferredHeapBase=0x100000000 

For the DNG server, we used a nursery (-Xmn) of 1/3 the maximum heap size.

Appendix F: Database server hardware

The database server that was used for the testing was IBM DB2 enterprise version 10.1.2. The same hardware and database settings were used for all of the performance tests, irrespective of the repository size.

For a database server, the team used an IBM System x3650 M4 with 2 x Intel Xeon E5-2640 2.5 GHz (six-core) and 64G of total RAM . The total number of processor cores/machines was 24. In the tests, one server was used for both the Jazz Team Server and RM databases. The database server that was used for the testing was IBM DB2 enterprise version 10.1.2. The same hardware and database settings were used for all of the performance tests, irrespective of the repository size.

In our tests, performance bottlenecks always formed first on the DNG server, due to the interactions around the disk-based indices. The database server was not the limited factor. However, the 6.0 release does use the database server more heavily for storing version information, so we expect that a higher end database server with fast disks) will improve performance as the number of versions and configurations increases.

Hard disk capacity and configuration

The database servers should use the RAID 10 configuration with the RAID controller configured with "write back cache." The team observed performance degradation in some use cases when using "write-through" caching. Use a high capacity and high performing hard disk (10K RPM or better).

Repository	Combined hard disk usage of the Jazz Team Server and RM databases	Hard disk size
Up to 500,000 artifacts	~100 GB	300 GB
Up to1 million artifacts	~150 GB	400 GB
Up to 2 million artifacts	~300 GB	700 GB

Appendix G: Proxy server hardware and configuration (for repositories of all sizes)

The team used the same server hardware to test repositories of all sizes. In general, the proxy server does not slow the performance of the RM server.

Processor

The team used IBM System x3250 M4 with 1 x Intel Xeon E3-1240v2 3.4 GHz (quad-core). The total number of processor cores/machines was 8.

IHS tuning

For the IHS systems that were used during the tests, in the server pool regulation section (worker.c) of httpd.conf file, these parameters were configured:

ThreadLimit	25
ServerLimit	100
StartServers	2
MaxClients	2500
SpareThreads	25
MaxSpareThreads	500
ThreadsPerChild	25
MaxRequestsPerChild	0

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External links:

• IBM

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