Aestiva H2O Web Site

Installation:
  Free Downloads
  The H2O Family
  Install Notes

Programming:
  Prerequisites
  H2O Whitepaper
  Online Manual
  Code Examples
  H2O Free Support

What's H2O?
H2O is programming made for the web.

What's it like?
H2O is English-like. If you know some Perl, VB, ASP, or PhP you'll be immediately productive in H2O. It runs on Linux, Mac, Unix, and Windows.

How do I try it?
Download H2O for free. Get it from hosting providers. Or buy on-line.

Where does H2O come from?
The language was invented by Aestiva. H2O stands for:
   HTML with
   HTML/OS
   Overlays.

HTML/OS CACHING

Introduction
This document gives a general description of HTML/OS caching. It describes how it works, and gives tips on optimizing performance.

HTML/OS caching is used by the HTML/OS engine to store temporary user data. The caching technique used by HTML/OS is called "On-demand Caching." This means that cache files are cleared away as needed, not when they expire. On-demand Caching has the advantage that it's very fast and takes minimum overhead away from the web server or your apps. This is unlike Browser caching techniques which make users wait as periodic maintenance is done. On-demand Caching does have a disadvantage of using more hard disk space than abolutely necessary.

How HTML/OS caching works?
In the Control Panel of HTML/OS the administrator is allowed to set up one or more "cache" folders (up to 99 folders may be specified). The more access to a site, the more folders needed. As a rule the administrator should set up one folder for every "200 new users per hour".

These folders are used to store temporary user information. When a new user is created a new user session ID is issued to the user. That ID is used to access user-specific information.

The cache for HTML/OS starts off holding data for IDs between 1 and 300. If HTML/OS encounters more than 300 users at one time the cache adjusts itself to hold data for IDs 1 to the last highest user ID.

Helpful tips and behaviors regarding the HTML/OS cache:
-- The default "timeout" for an inactive user is 100 minutes. Depending on the number of users, if the timeout is increased the size of the cache directory may become larger. The larger the cache directory, the more disk space used, resulting in slower caching. The reason for this happening is as follows. The inactive user is not increasing the size of the cache directory, but they do take up their existing space until their time expires. During this time period, the active user's file size may grow larger, and files may be added to the cache directory by new users. Hence the larger the hard disk usage. The timeout for an inactve user can be adjusted in the HTML/OS Control Panel under menu item User Timeout.

-- HTML/OS reserves a minimum of 300 ID sets. There will not be much clean up until there are more than 1,500 files in the caching folder.

-- When writing code keep the HTML/OS variables under 50K each (in other words, set large variables to "ERROR" before the end of a page if the variable is 50K or more.) For example, if there is a 500K variable and many users, then 300 users saved in cache would eat up 150 Meg. While this may not be a lot of hard disk space on a dedicated server, on hosted servers with disk quotas this can be a problem. For more information about clearing variables, read the article Clearing Variables.

-- Do not use telnet or ftp to delete files in the cache directory except in emergency situations where all the files need to be deleted (which is okay). If using a command line
program running from "cron" to delete files, call the CLEANCACHE tag to clean the cache folders.

-- If a site uses full "start" links to go from page to page, it will generate new user session files for each link. One way to avoid that, is to use the "nosession" URL. This feature can be used on pages that do not contain hypertext links and HTML forms that refer to HTML/OS pages or Overlays. This option can be used with Start-links that push images or stand-alone documents. Using the "nosession" URL prevents unnecessary files from being created. See the HTML/OS control panel for help on that topic.

Summary
Understanding how HTML/OS caching works, helps the programmer to write better code. With this knowledge code can be written to run faster and more efficiently. Having fast and efficient code makes a much better environment for the end user.