A location or process for storing of transitory or temporary data in order to improve application or system performance.

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51
votes
10answers
8k views

Why drop caches in Linux?

In our servers we have a habit of dropping caches at midnight. sync; echo 3 > /proc/sys/vm/drop_caches When I run the code it seems to free up lots of RAM, but do I really need to do that. ...
36
votes
3answers
23k views

Disable caching when serving static files with Nginx (for development)

We are using Nginx to serve static files on a development platform. As it is a development platform, we'd like to disable caching so that each change is propagated to the server. The configuration of ...
30
votes
5answers
22k views

Which PHP (opcode) cache one should use and why?

I keep hearing about some PHP (opcode) caches like - APC, XCache, Memcache, eAccelerator, etc. But I couldn't ever figure out how to go about choosing one. Apart from performance benefit, which a ...
17
votes
3answers
4k views

How effective is LSI CacheCade SSD storage tiering?

LSI offers their CacheCade storage tiering technology, which allows SSD devices to be used as read and write caches to augment traditional RAID arrays. Other vendors have adopted similar ...
15
votes
3answers
6k views

Is there a way to get Cache Hit/Miss ratios for block devices in Linux?

Is it possible to see in Linux how many read and write requests from user space end up causing cache hits and misses for block devices?
13
votes
6answers
8k views

SATA Disks that handle write caching properly?

It's pretty common to see advice to disable the write cache on individual disks used for databases because otherwise some disks will acknowledge writes that haven't yet made it to the disk surface. ...
13
votes
1answer
5k views

deleting linux cached ram [duplicate]

I have a webserver that has 8GB of ram and is running a pretty intensive php site (1 site) that does file manipulation, graphing, emailing, forums, you name it. The environment is far from static ...
13
votes
1answer
4k views

Hardware RAID controller cache battery failure frequency/lifetime?

I'm in an environment that contains many Supermicro servers equipped with Adaptec and LSI MegaRAID hardware RAID controllers. These controllers contain battery-backed cache modules to help boost write ...
12
votes
7answers
5k views

SQL Server - Force DB in memory?

We have a beefy Windows 2008 x64 server (4 x 4 core CPU, 32GB RAM) running SQL Server 2005 64-bit. We have a small (6GB) but very important database that is somewhat slow to access until the pages are ...
12
votes
3answers
4k views

How do I remove a specific bad plan from the SQL Server query cache?

We have one particular SQL Server 2008 query (not a stored proc, but the same SQL string -- executes every 5 minutes) that intermittently caches a very bad query plan. This query normally runs in a ...
12
votes
1answer
8k views

For L2ARC and ZIL: is it better to have one large SSD for both, or two smaller SSDs?

Main references ZFS L2ARC (Brendan Gregg) (2008-07-22) and ZFS and the Hybrid Storage Concept (Anatol Studler's Blog) (2008-11-11) include the following diagram: Question Should I interpret the ...
11
votes
2answers
9k views

Varnish Cache - default TTL?

I have discovered that I can set the TTL in Varnish as follows in my VCL file: sub vcl_fetch { # 1 minute set obj.ttl = 1m; } But what is the default setting (assuming the backend server is ...
11
votes
3answers
5k views

Tuning Linux disk caching behaviour for maximum throughput

I'm running into a maximum throughput issue here and need some advice on which way to tune my knobs. We're running a 10Gbit fileserver for backup distribution. It's a two disk S-ATA2 setup on an LSI ...
9
votes
2answers
2k views

ZFS and cache devices

I'm going to add a SSD drives to my ZFS storages as a cache. Anyone has any experience with this? What if cache device dies, will the any data be affected?
9
votes
1answer
2k views

Managing battery relearn cycles on LSI and similar RAID controllers

How do engineers deal with RAID controller battery "relearn" cycles? As noted in: What's a "battery relearn" on a LSI MegaRaid?, relearn cycle discharges the RAID controller battery ...
8
votes
2answers
3k views

High disk I/O when cache is used?

A few days ago I noticed a disk I/O wait and disk activity drop (which was great). Then I also notice that my cache was full(*) and fragmented. Then I flushed cache. After that, disk latency and disk ...
8
votes
5answers
20k views

Is there a way to turn off client browser caching for specific websites?

This is a browser agnostic question but we're testing with IE9. One of the web apps our users visit is being randomly cached and changes aren't showing up when they should. No other site has this ...
8
votes
1answer
1k views

How does Varnish deal with running out of storage?

I am using Varnish 3.0.3 (the latest as of this writing) with more or less the default install, using the following for storage: # # Cache file location ...
7
votes
1answer
939 views

Vagrant NFS share doesn't show updated file if size doesn't change

When mounting /vagrant over NFS, a changed file on the host is not refresh on the guest if the size doesn't changes. Quick update/typo are not immediately reflected unless I make enough modification ...
7
votes
2answers
825 views

ISP grade Proxy

We are a ISP in Africa (bandwidth is expensive, more than 800 USD per Mbit). Instead of investing in more bandwidth I believe it can be worthy to invest on web proxy appliance. I prefer to use mature ...
7
votes
4answers
16k views

How to solve “ExpiresActive not allowed here” error message in .htaccess file?

I am trying to add Expires headers to the HTTP responses of the site I am working on. The only way for me to control the Apache 1.3 server is by editing my .htaccess file. I tried adding code such as ...
7
votes
5answers
5k views

Squid or Other HTTP Caches with SSD Cache Store?

I'm contemplating setting up a squid (or possibly varnish) cache on a system with SSD drives. The obvious benefit is that these systems have great READ speeds and I expect my hit ratios to be fairly ...
7
votes
3answers
15k views

How do I flush IIS Cache without restarting web server?

I have a web site IIS 6.0 that places data into the cache. Sadly it hasn't had a expiration set on it. Is there a way (utility or command) to force this cache to be cleared without rebooting the ...
7
votes
2answers
2k views

Apache cache serving partial content 206 responses to requests for the full content

We're running Plone 3.3.6 behind Apache 2.2.19 with mod_cache. We've recently noticed that Apache is caching the 206 response to a range request and then serving that partial response when a request ...
7
votes
2answers
1k views

Can enabling a RAID controller's writeback cache harm overall performance?

I have an 8 drive RAID 10 setup connected to an Adaptec 5805Z, running Centos 5.5 and deadline scheduler. A basic dd read test shows 400mb/sec, and a basic dd write test shows about the same. When I ...
7
votes
1answer
177 views

Backup process flushes disk cache

I've got a backup process which reads quite a lot of data from disk, and therefore uses up all memory for disk cache, swapping off apps and other cached data in the process. There is no benefit to ...
6
votes
3answers
5k views

What purpose does the battery serve on a battery-backed caching RAID controller if the server is on an uninterruptible power supply?

Is the battery redundant if the server is on a properly-sized UPS? There is an option to force write-back mode and I want to understand the risk. It is my understanding that it helps against power ...
6
votes
5answers
3k views

Free / Cached / Available memory on Linux

I have read that linux uses free memory for caching, to make system faster. However, both Nagios and Paessler PRTG monitoring system show me that my memory usage is critical. I could change Nagios ...
6
votes
2answers
785 views

Force request to miss cache but still store the response

I have a slow web app that I've placed Varnish in front of. All of the pages are static (they don't vary for a different user), but they need to be updated every 5 minutes so they contain recent data. ...
6
votes
2answers
1k views

Apache: Send pre-packed gzip'ed files

I want Apache to send static files gzip'ed over the wire, but also want Apache to not always gzip them over and over again. So I thought if it wouldn't be possible to deliver an .gz file if it exists. ...
6
votes
2answers
4k views

Squid not caching

I am trying to configure Squid as a caching server. I have a LAN where The webserver (apache) is at 192.168.122.11 squid is at 192.168.122.21 and my client is at 192.168.122.22. The problem is, when I ...
6
votes
2answers
25k views

Clearning Chrome SSL cache?

I have a haproxy / stunnel server that handles SSL for our sites on AWS. During testing I created a self signed cert on this server and hit it from my desktop using Chrome to test that stunnel was ...
6
votes
1answer
4k views

Working Nginx fastcgi_cache php-fpm cache and static file caching configuration?

Nginx wiki is very vague with explanation as to how to properly setup nginx with php-fpm with fastcgi_caching for sites which have cookies i.e. wordpress, drupal, vbulletin etc. I downloaded a ...
6
votes
11answers
751 views

DNS as distributed cache

We have a use case to cache 300+ million pieces of such data each with a unique key. I know this is unorthodox but, it has been suggested at my company that DNS could be used as a fast distributed ...
6
votes
1answer
470 views

Squid 3 reloading makes it stop serving requests

So, we use Squid 3 here (3.0.STABLE8-3+lenny4), pretty standard configuration (no dansguardian or similar) + NTLM authentication with LDAP background, circa 1000 users on a busy day, and our acls ...
6
votes
3answers
3k views

Configuring Windows DNS resolver cache

I asked this question on Stack Overflow several months ago and didn't get any useful answers. Perhaps somebody here has better info. Note that I'm talking about the client DNS resolver cache. This ...
6
votes
2answers
3k views

Can you set a minimum linux disk buffer size?

I have a rather old Linux machine with 2GB of ram, no swap, and it's working very well, with the system using every unused piece of memory for caching with great effect. However, when I'm close to ...
5
votes
6answers
9k views

Does my ISP cache the DNS?

I went to my zoneedit.com, changed mydomain.com to point to a different IP. But changes haven't taken affect yet. Is this because my ISP DNS is caching?
5
votes
3answers
8k views

Configuring Varnish to rewrite Expires/Cache-Control headers for client-side caching

How do I configure Varnish so that all responses to requests matching say "*.css" gets cached in the client's browser for 30 days? What I'm trying to achieve is making Varnish set the correct ...
5
votes
2answers
12k views

How can I cache YouTube videos with Squid Cache?

we're using the Squid cache in our company. Is there any way we can cache YouTube videos? cheers :)
5
votes
1answer
2k views

What is the difference between a cache, a primed cache and an empty cache?

Can someone explain the following concepts to me as the relate to measuring the data transfer of data from my web site. Whats the difference between a cache, a primed cache and an empty cache? Can ...
5
votes
4answers
5k views

How much impact does hard drive cache have on IO performance

How much impact does hard drive cache have on IO performance Are there any statistics or performance tests available that can tell me if there is a difference is 16MB vs 32MB Cache? If it matters, I ...
5
votes
2answers
8k views

Varnish configuration to only cache for non-logged in users

I have a Ruby on Rails application fronted by varnish+nginx. As most of the sites content is static unless you are a logged in user, I want to cache the site heavily with varnish when a user is logged ...
5
votes
2answers
803 views

Linux disable disk cache for a single command

Our server is performing decently, but when backups or other scan processes run it will tank the entire server. Something like clamd will run and scan many files. While we expect slow performance, ...
5
votes
3answers
4k views

Making SATA disk write cache safe

Supposedly (see, e.g., a question about it here), with NCQ enabled drives, the drive write cache is supposed to be safe, as in it doesn't like to the OS about data being committed to the platters when ...
5
votes
1answer
1k views

Linux; What is stripe_cache_size and what does it do?

I am currently building a software RAID under Linux using mdadm utility and I've read a few articles that describe how to increase the stripe_cache_size value for that RAID and how to calculate an ...
5
votes
4answers
3k views

Slow Memcached: Average 10ms memcached `get`

We're using Newrelic to measure our Python/Django application performance. Newrelic is reporting that across our system "Memcached" is taking an average of 12ms to respond to commands. Drilling down ...
5
votes
7answers
3k views

Windows explorer (filename) string corruption when using remote desktop?

Has anyone else experienced this problem? While browsing folders in explorer over a remote desktop connection, sometimes the file name strings will get corrupted, so they display incorrectly in ...
5
votes
1answer
940 views

Use Cherokee Instead of nginx in Front of Varnish to Get HTTP 1.1 Optimizations?

We have been running nginx -> uWSGI, and now we are evaluating putting Varnish as a caching layer between nginx and uWSGI (similar to http://www.heroku.com/how/architecture). But, nginx only supports ...
5
votes
1answer
1k views

Linux buffer cache effect on IO writes?

I'm copying large files (3 x 30G) between 2 filesystems on a Linux server (kernel 2.6.37, 16 cores, 32G RAM) and I'm getting poor performance. I suspect that the usage of the buffer cache is killing ...