EasyIndex can generate thumbnails as it needs them. That is, if a correctly sized thumbnail doesn't exist when an index is displayed, EasyIndex will generate it and save it to the server disk so it won't need to be generated again. This works just fine when there's only one or two thumbnails to be generated (like when you have just added a new post) but when EasyIndex displays an index for the very first time, there may be dozens, or even hundreds of thumbnails to be generated. In that case, the index page might appear to stall for minutes while the thumbnails are generated.
To stop this from happening, you can tell EasyIndex to generate all the thumbnails required for an index before you publish it. You can do that by clicking the "Generate Thumbnails" button above the "Publish" button when you create an index.
There are two ways the thumbnail generator works. The first is to start the generation in the server background and process all the thumbnails in a batch. The second method generates the thumbnails a few at a time.
This is by far the quickest way to generate thumbnails. When you click the Generate Thumbnails button, a message is sent to your server which starts the background process running. Every 2 seconds after that, the index create/edit page queries the server to get the status of the generation and updates the progress on your screen. Unfortunately, some web hosts are unable to handle the way background tasks are initiated, and in this case, you'll need to use the alternative method. You can test if your server can process in background by clicking the "Test" button on the General tab of the EasyIndex settings page. Background generation is only available in the Plus version of EasyIndex.
In this mode, when you click the "Generate Thumbnails" button a message is sent to the server to generate as many thumbnails as it can in a short period of time. After the time limit expires, the generator stops what it's doing and returns a message to the create/edit page which updates the progress bar before calling the generator again to process more. The reason it can only run for a relatively short period is that if it was allowed to run to completion, the Index create/edit page in your browser would likely "time out" (i.e. think the server was unresponsive) and give up. Also, there would be no indication of the progress of the generator if it ran uninterrupted for long periods.
To prevent the generator running forever and to detect situations where the generator terminates abnormally, there is a time limit on how long it can run. You specify this on the General tab of the EasyIndex settings page.
For background generation, we'd suggest 5 minutes should be ample, but if your server is underpowered and/or you have a huge number of thumbnails to generate, more time may be needed. If the generator does time out but otherwise runs normally, you can click the "Generate Thumbnails" button again and the generator will pick up where it left off.
For the alternative generation method, we'd recommend you use around 5 seconds for the "timeout". In this case, the generator will generate as many thumbs as it can in that time and then return to the Index create/edit page so it can update the run progress before calling the generator again.
Making thumbnails can use a significant amount of PHP memory on your server. You can set the amount of memory EasyIndex will reserve before creating thumbnails in the Thumbnail memory option on the EasyIndex settings page.