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• Nagios remote monitoring: NRPE Vs. SSH

  - by sam

  We use Nagios to monitor quite a few (~130) servers. We monitor CPU, Disk, RAM and a few other things on each server. I've always used SSH to run the remote commands, purely because it requires little to no additional config on the remote server, just install nagios-plugins, create the nagios user and add the SSH key, all of which I've automated into a shell script. I've never actually considered the performance implications of using SSH over NRPE. I'm not too bothered about the load hit on the Nagios server (It's probably over-speced for what it does, it's never been over 10% CPU), but we run each remote check every 30 seconds and each server has 5 different checks performed. I assume SSH requires more resources for each check but is there a huge difference? (I.E. enough of a difference to warrant the switch to NRPE). If it's any help, we monitor a mix of physical servers (Normally with 8, 12 or 16 physical cores) and Amazon EC2 medium/large instances.

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• MySQL Unions/Subselects not utilizing keys from associated tables

  - by Brett

  I've noticed by doing EXPLAINs that when a MySQL union between two tables is used, mysql creates a temporary table, but the temp table does not use keys, so queries are slowed considerably. Here is an example: SELECT * FROM ( SELECT `part_number`, `part_manufacturer_clean`, `part_number_clean`, `part_heci`, `part_manufacturer`, `part_description` FROM `new_products` AS `a` UNION SELECT `part` as `part_number`, `manulower` as `part_manufacturer_clean`, `partdeluxe` as `part_number_clean`, `heci` as `part_heci`, `manu` as `part_manufacturer`, `description` as `part_description` FROM `warehouse` AS `b` ) AS `c` WHERE `part_manufacturer_clean` = 'adc' EXPLAIN yields this: id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY <derived2> ALL (NULL) (NULL) (NULL) (NULL) 17206 Using where 2 DERIVED a ALL (NULL) (NULL) (NULL) (NULL) 17743 3 UNION b ALL (NULL) (NULL) (NULL) (NULL) 5757 (NULL) UNION RESULT <union2,3> ALL (NULL) (NULL) (NULL) (NULL) (NULL) In this case, part_manufacturer_clean and manulower are keys in both tables. When I don't use the subselects and union, and just use one table, everything works fine. I'm not sure if the issue is with the union or with the subselects. Is there any way to union two tables and still use keys/indexes for performance?

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• High Lock Wait ratio in MySQL

  - by FunkyChicken

  on my site I log every pageview (date,ip,referrer,page,etc) in a simple mysql table. This table gets very little selects (3 per minute), but a lot of inserts. (about 100 per second) Today I changed this table from an InnoDB table to a MEMORY table, this made sense to me to prevent unnecessary hard disk IO. I also prune this table once per minute, to make sure it never get's too big. -- Performance wise, things are running fine. But I noticed that while running tuning-primer, that my Current Lock Wait ratio is quite high. Current Lock Wait ratio = 1 : 561 My question: Should I worry about this Lock Wait Ratio? And is there something I can change in my my.cnf to improve things so that the lock wait ratio isn't so high?

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• need for tcp fine-tuning on heavily used proxy server

  - by Vijay Gharge

  Hi all, I am using squid like Internet proxy server on RHEL 4 update 6 & 8 with quite heavy load i.e. 8k established connections during peak hour. Without depending much on application provider's expertise I want to achieve maximum o/p from linux. W.r.t. that I have certain questions as following: How to find out if there is scope for further tcp fine-tuning (without exhausting available resources) as the benchmark values given by vendor looks poor! Is there any parameter value that is available from OS / network stack that will show me the results. If at all there is scope, how shall I identify & configure OS tcp stack parameters i.e. using sysctl or any specific parameter Post tuning how shall I clearly measure performance enhancement / degradation ?

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• When using RAID10 + BBWC why is it better to separate PostgreSQL data files from OS and transaction logs than to keep them all on the same array?

  - by Vlad

  I've seen the advice everywhere (including here and here): keep your OS partition, DB data files and DB transaction logs on separate discs/arrays. The general recommendation is to use RAID1 for OS, RAID10 for data (or RAID5 if load is very read-biased) and RAID1 for transaction logs. However, considering that you will need at least 6 or 8 drives to build this setup, wouldn't a RAID10 over 6-8 drives with BBWC perform better? What if the drives are SSDs? I'm talking here about internal server drives, not SAN.

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• How can I tell if my live web-server is overloaded?

  - by Nick G

  We have a live webserver which doesn't seem to be performing all that well. It's a Dell PowerEdge machine, a few years old (dual core, 4GB) which is hosting about 20 low-traffic websites. However it doesn't seem to be as fast as it used to be. How can we determine the cause of this? If it's website traffic, I would be expecting high CPU but CPU usage is quite low and hovers around the 15-30% mark except for very brief periods. I'm wondering perhaps, if rather than CPU performance being a problem, perhaps it's disk thrashing due to the constant read/writes of all the small web files and database queries. It has 4x 7200 RPM SATA drives in RAID 5. So is there a way to check that it's not disk thrashing?

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• writting becomes slow after few writes

  - by user1566277

  I am running an embedded Linux on arm with a SD-Card. While writing huge amounts of data I see bizarre effects. E.g, when I dd a 15 MB file few times, it writes the file (normally) in less than 2 Secs. But After lets say 3-4 times it takes sometimes 15 to 30 Seconds to write the same file. If I sync after writing the file, then this does not happen but sync takes long time too. If there is enough gap between writing two files than presumably kernel syncs itself. How can I optimize the whole performance so that write should always finish inside 2 Seconds. The File system I am using is ext3. Any pointers?

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• Postfix smarthost with diffent relayhosts and sender dependant authentication

  - by mattinsalto

  I've setup postfix as smarthost with different relayhosts and sender dependant authentication. Everything works ok, but I have a performance question. Is it better to send all the email corresponding to a domain through only one account? I mean, now I'm sending each message authenticating to the relay host with the sender credentials. Example: If I have 5 email accounts and I send 10 simultaneous messages from each account, How many times is postfix login to the relay host if I have sender dependant authentication? 5 times? once for each sender 50 times? once for each message If I send all the messages corresponding to one realy host through one account, how many times does postfix login to the relay host? only once? Thanks in advance.

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• Poor TCP loopback throughput on Windows

  - by Yodan Tauber

  I measured the throughput of a locally bound TCP socket connection on my computer (Intel Q9550, 64 GB RAM, Windows XP 64 bit) using iperf. I got dissatisfying results (around 1.6 Gbit/s) each time, no matter how I tweaked the TCP settings (buffer length, window size, max segment size, no delay). I got similar results when I tried netperf. Now, I understand (from sources like these) that the average throughput of a loopback connection should be around 5 Gbit/s. What could be the reasons for such poor performance?

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• How fast can a Windows 2008 CIFS client write to SAMBA server using 10Gb NIC?

  - by one_bsd_guy

  We are experiencing a performance problem using Windows 2008 CIFS client. We have a FreeNAS server that delivers 1.3GB/s on ZFS write. We have 10Gb network connecting NAS server and CIFS clients. Using two Linux CIFS clients, we can get around 1.2GB/s. But windows 2008 clients can only give us 400MB/s. Is that the best a Windows 2008 client can deliver or we do have a poorly configured Windows client? Much appreciated.

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• Why won't Windows use the other CPU cores?

  - by revloc02

  In Windows Task Manager the Performance tab shows the first CPU maxed out, the other 7 just idling along with the occasional spike. What gives? More info: I've got 8GB and only 4.5GB are being used. The Processes tab has no indication of any process hogging processing power. In fact System Idle Process is 98-99. When I program stuff and have like 8 to 12 applications going (several directly unrelated to programming of course) my computer slows to a crawl. Sysyem Info: Intel Core i7-2600K Processor (quad-core with hyper-threading), 8GB RAM, Intel BOXDZ68BC LGA 1155 Motherboard, 500GB HDD

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• Enterprise Level Monitoring Solution

  - by Garthmeister J.

  My company is currently looking to replace our current solution used for monitoring our web-based enterprise solutions for both up-time and performance. Please note this is not intended to be a network monitoring-type solution (internally we currently use Nagios). If anyone has a provider that they have had a positive experience with, it would be much appreciated. Here is a list of our requirements: • Must have a large number of probes/agents around the globe to be representative of our customer base • Must have a flexible scripting capability to automate multi-step user actions • 24 hour a day monitoring • Flexible alerting system • Report generation capability • Mimic browser specific monitoring (optional, not a must-have)

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• How do I stop my IIS App Pool making a request to wpad.mydomain.com?

  - by Programming Hero

  As part of some performance troubleshooting, I've monitored the slow startup of a "cold" App Pool (one without an active worker process) in IIS. When using a built-in account, the App Pool starts in sub-second time. When using a custom local account the App Pool takes 30+ seconds to start processing requests. The service appears to be making requests to wpad.mydomain.com, an address it does not have access to, which causes it to wait 30 seconds for a response before eventually timing out. As a workaround, I've added the hostname to the server's hosts file, to direct the traffic to the local machine, which returns much faster (1-2 seconds). What do I need to do to stop IIS making this request when this identity is used for the App Pool?

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• Specific apache + mysql settings for a light-weight site

  - by Good Person

  I have a small website with a Joomla and a Moodle set up. It seems that both of these are very slow. The server (CentOS release 5.5 (Final)) is a virtual dedicated server with about 2GB of ram. I don't expect to ever get more than 10-15 people on at the same time (and if that is high) What settings could I change in either apache, mysql, or even the OS to increase the performance of my site? I'm not concerned about running out of resources if I get too many visitors. If you need more specific data leave a comment and I'll edit the question.

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• Is virtual machine slower than the underlying physical machine?

  - by Michal Illich

  This question is quite general, but most specifically I'm interested in knowing if virtual machine running Ubuntu Enterprise Cloud will be any slower than the same physical machine without any virtualization. How much (1%, 5%, 10%)? Did anyone measure performance difference of web server or db server (virtual VS physical)? If it depends on configuration, let's imagine two quad core processors, 12 GB of memory and a bunch of SSD disks, running 64-bit ubuntu enterprise server. On top of that, just 1 virtual machine allowed to use all resources available.

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• Relating ping to perceived browser GUI response

  - by cvsdave

  We periodically get complaints of poor GUI (browser page) response that we need to explore. I am looking for a quick and cheap first check to see if the issue is network latency, or server performance. Has anyone encountered any discussion of ping time and perceived GUI response? I understand that GUI response is complicated, but it would be nice if we could find or develop a rule of thumb along the lines of "Hmmmm, ping is over 200, it might be network problems". Ideally, this lives in a script on the user's machine so that we can see the latency that they are seeing... (BASH, Linux). A reference to a good discussion page would be a fine answer, as would any recommendation of other source material.

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• Why are browsers so heavy?

  - by Kaivosukeltaja

  Back in 1998 I had a computer with 233MHz Pentium MMX CPU and a GFX card with no 3D acceleration. It was able to run games like Quake II at a decent FPS rate. My current computer has tons more performance and a mid-class GPU, yet struggles to reach 20 FPS when rendering a single model inside a skybox with WebGL. Even regular pages with lots of 2D CSS animations bring many modern computers to their metaphorical knees. As a web developer I understand there's a lot going on in a web page but not what makes it that heavy. Modern browsers compile JavaScript to CPU native machine code before running it and rendering into a canvas element shouldn't trigger DOM rebuilds so theoretically it should be a lot faster than it is. What am I missing here and is it possible to avoid or minimize whatever is making the browsers slow to build more efficient websites?

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• Monitoring disk block access in Linux

  - by VoidPointer

  Is there a way to gather statistics about blocks being accessed on a disk? I have a scenario where a task is both memory and I/O intensive and I need to find a good balance as to how much of the available RAM I can assign to the process and how much I should leave for the system for building its I/O cache for the block device being used. I suspect that most of the I/O that is currently happening is accessing a rather small subset of the device and that performance could be optimized by increasing the RAM that is available for I/O buffering. Ideally, I would be able to create something like a "heat-map" that shows me which parts of the disk are accessed most of the time.

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• Computers with Small Capacity SSD - For caching?

  - by RXC

  Recently, in newsletters from websites, I have been seeing computers for sale from manufacturers that include an HDD and an SSD but the SSD has a small capacity like 24 GBs. I don't know if this still holds true, but I learned that when building a computer, you would want to install your OS on your fastest hard drive. I do a lot of PC gaming, so I install my OS and games on my SSD, because I learned that games and many applications make lots of system calls to the OS and performance can only be as fast as the slowest piece. Why these computers come with small capacity SSDs? Most OS's take up around 20 to 30 GBs of space, so what are the benefits of such a small SSD? Are these small size SSDs for caching? and what exactly does caching mean (what does it do and how does it help)?

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• How does Google manage to serve results so fast?

  - by Quintin Par

  I am building an autocomplete functionality for my site and the Google instant results are my benchmark. When I look at Google, the 50-60 ms response time baffle me. They look insane. In comparison here’s how mine looks like. To give you an idea my results are cached on the load balancer and served from a machine that has httpd slowstart and initcwnd fixed. My site is also behind cloudflare From a server side perspective I don’t think I can do anything more. Can someone help me take this 500 ms response time to 60ms? What more should I be doing to achieve Google level performance?

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• Stale statistics on a newly created temporary table in a stored procedure can lead to poor performance

  - by sqlworkshops

  When you create a temporary table you expect a new table with no past history (statistics based on past existence), this is not true if you have less than 6 updates to the temporary table. This might lead to poor performance of queries which are sensitive to the content of temporary tables.I was optimizing SQL Server Performance at one of my customers who provides search functionality on their website. They use stored procedure with temporary table for the search. The performance of the search depended on who searched what in the past, option (recompile) by itself had no effect. Sometimes a simple search led to timeout because of non-optimal plan usage due to this behavior. This is not a plan caching issue rather temporary table statistics caching issue, which was part of the temporary object caching feature that was introduced in SQL Server 2005 and is also present in SQL Server 2008 and SQL Server 2012. In this customer case we implemented a workaround to avoid this issue (see below for example for workarounds).When temporary tables are cached, the statistics are not newly created rather cached from the past and updated based on automatic update statistics threshold. Caching temporary tables/objects is good for performance, but caching stale statistics from the past is not optimal.We can work around this issue by disabling temporary table caching by explicitly executing a DDL statement on the temporary table. One possibility is to execute an alter table statement, but this can lead to duplicate constraint name error on concurrent stored procedure execution. The other way to work around this is to create an index.I think there might be many customers in such a situation without knowing that stale statistics are being cached along with temporary table leading to poor performance.Ideal solution is to have more aggressive statistics update when the temporary table has less number of rows when temporary table caching is used. I will open a connect item to report this issue.Meanwhile you can mitigate the issue by creating an index on the temporary table. You can monitor active temporary tables using Windows Server Performance Monitor counter: SQL Server: General Statistics->Active Temp Tables. The script to understand the issue and the workaround is listed below:set nocount onset statistics time offset statistics io offdrop table tab7gocreate table tab7 (c1 int primary key clustered, c2 int, c3 char(200))gocreate index test on tab7(c2, c1, c3)gobegin trandeclare @i intset @i = 1while @i <= 50000begininsert into tab7 values (@i, 1, ‘a’)set @i = @i + 1endcommit trangoinsert into tab7 values (50001, 1, ‘a’)gocheckpointgodrop proc test_slowgocreate proc test_slow @i intasbegindeclare @j intcreate table #temp1 (c1 int primary key)insert into #temp1 (c1) select @iselect @j = t7.c1 from tab7 t7 inner join #temp1 t on (t7.c2 = t.c1)endgodbcc dropcleanbuffersset statistics time onset statistics io ongo–high reads as expected for parameter ’1'exec test_slow 1godbcc dropcleanbuffersgo–high reads that are not expected for parameter ’2'exec test_slow 2godrop proc test_with_recompilegocreate proc test_with_recompile @i intasbegindeclare @j intcreate table #temp1 (c1 int primary key)insert into #temp1 (c1) select @iselect @j = t7.c1 from tab7 t7 inner join #temp1 t on (t7.c2 = t.c1)option (recompile)endgodbcc dropcleanbuffersset statistics time onset statistics io ongo–high reads as expected for parameter ’1'exec test_with_recompile 1godbcc dropcleanbuffersgo–high reads that are not expected for parameter ’2'–low reads on 3rd execution as expected for parameter ’2'exec test_with_recompile 2godrop proc test_with_alter_table_recompilegocreate proc test_with_alter_table_recompile @i intasbegindeclare @j intcreate table #temp1 (c1 int primary key)–to avoid caching of temporary tables one can create a constraint–but this might lead to duplicate constraint name error on concurrent usagealter table #temp1 add constraint test123 unique(c1)insert into #temp1 (c1) select @iselect @j = t7.c1 from tab7 t7 inner join #temp1 t on (t7.c2 = t.c1)option (recompile)endgodbcc dropcleanbuffersset statistics time onset statistics io ongo–high reads as expected for parameter ’1'exec test_with_alter_table_recompile 1godbcc dropcleanbuffersgo–low reads as expected for parameter ’2'exec test_with_alter_table_recompile 2godrop proc test_with_index_recompilegocreate proc test_with_index_recompile @i intasbegindeclare @j intcreate table #temp1 (c1 int primary key)–to avoid caching of temporary tables one can create an indexcreate index test on #temp1(c1)insert into #temp1 (c1) select @iselect @j = t7.c1 from tab7 t7 inner join #temp1 t on (t7.c2 = t.c1)option (recompile)endgoset statistics time onset statistics io ondbcc dropcleanbuffersgo–high reads as expected for parameter ’1'exec test_with_index_recompile 1godbcc dropcleanbuffersgo–low reads as expected for parameter ’2'exec test_with_index_recompile 2go

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• Windows system monitoring and profiling

  - by Aris

  I have several dozen 64-bit Windows 2003 servers in a high performance environment with very bursty system utilization. I am looking for a tool (or tools) to monitor and analyze system performance (eg, CPU utilization, bandwidth, etc). This tool can either query servers from a central location (SNMP) or require installation of a component on each server. It should poll on a 1-second interval. It should be able to generate pretty graphs which show trends over time. As a nice-to-have, it should be able to send out emails or IMs when certain thresholds are exceeded. The tools I have investigated so far, including Solarwinds and PRTG, are not designed to poll this frequently. They seem to be designed for a ~30-second interval. Solarwinds wouldn't go lower than 3-sec, and PRTG chokes at 1-sec. They both default to 1-min. All three tools seem more focused on outage monitoring and reporting than metric collection. Given the bursty nature of our applications, such infrequent polling would result in a very inaccurate picture of performance. I am considering rolling my own solution using perfmon. This would be a lot of work, and seems like reinventing the wheel. Are there any tools out there that meet my needs?

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• How to modernize an enormous legacy database?

  - by smayers81

  I have a question, just looking for suggestions here. So, my application is 'modernizing' a desktop application by converting it to the web, with an ICEFaces UI and server side written in Java. However, they are keeping around the same Oracle database, which at current count has about 700-900 tables and probably a billion total records in the tables. Some individual tables have 250 million rows, many have over 25 million. Needless to say, the database is not scaling well. As a result, the performance of the application is looking to be abysmal. The architects / decision makers-that-be have all either refused or are unwilling to restructure the persistence. So, basically we are putting a fresh coat of paint on a functional desktop application that currently serves most user needs and does so with relative ease and quick performance. I am having trouble sleeping at night thinking of how poorly this application is going to perform and how difficult it is going to be for everyday users to do their job. So, my question is, what options do I have to mitigate this impending disaster? Is there some type of intermediate layer I can put in between the database and the Java code to speed up performance while at the same time keeping the database structure intact? Caching is obviously an option, but I don't see that as being a cure-all. Is it possible to layer a NoSQL DB in between or something?

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• Preloading Winforms

  - by msarchet

  I am currently working on a project where we have a couple very control heavy user controls that are being used inside a MDI Controller. This is a Line of Business app and it is very data driven. The problem that we were facing was the aforementioned controls would load very very slowly, we dipped our toes into the waters of multi-threading for the control loading but that was not a solution for a plethora of reasons. Our solution to increasing the performance of the controls ended up being to 'pre-load' the forms onto a hidden window, create a stack of the existing forms, and pop off of the stack as the user requested a form. Now the current issue that I'm seeing that will arise as we push this 'fix' out to our testers, and the ultimately our users is this: Currently the 'hidden' window that contains the preloaded forms is visible in task manager, and can be shut down thus causing all of the controls to be lost. Then you have to create them on the fly losing the performance increase. Secondly, when the user uses up the stack we lose the performance increase (current solution to this is discussed below). For the first problem, is there a way to hide this window from task manager, perhaps by creating a parent form that encapsulates both the main form for the program and the hidden form? Our current solution to the second problem is to have an inactivity timer that when it fires checks the stacks for the forms, and loads a new form onto the stack if it isn't full. However this still has the potential of causing a hang in the UI while it creates the forms. A possible solutions for this would be to put 'used' forms back onto the stack, but I feel like there may be a better way.

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• SQL Server Multi-statement UDF - way to store data temporarily required

  - by Kharlos Dominguez

  Hello, I have a relatively complex query, with several self joins, which works on a rather large table. For that query to perform faster, I thus need to only work with a subset of the data. Said subset of data can range between 12 000 and 120 000 rows depending on the parameters passed. More details can be found here: http://stackoverflow.com/questions/3054843/sql-server-cte-referred-in-self-joins-slow As you can see, I was using a CTE to return the data subset before, which caused some performance problems as SQL Server was re-running the Select statement in the CTE for every join instead of simply being run once and reusing its data set. The alternative, using temporary tables worked much faster (while testing the query in a separate window outside the UDF body). However, when I tried to implement this in a multi-statement UDF, I was harshly reminded by SQL Server that multi-statement UDFs do not support temporary tables for some reason... UDFs do allow table variables however, so I tried that, but the performance is absolutely horrible as it takes 1m40 for my query to complete whereas the the CTE version only took 40minutes. I believe the table variables is slow for reasons listed in this thread: http://stackoverflow.com/questions/1643687/table-variable-poor-performance-on-insert-in-sql-server-stored-procedure Temporary table version takes around 1 seconds, but I can't make it into a function due to the SQL Server restrictions, and I have to return a table back to the caller. Considering that CTE and table variables are both too slow, and that temporary tables are rejected in UDFs, What are my options in order for my UDF to perform quickly? Thanks a lot in advance.

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