Here's a sound approach - drop the .gif files. Use .png files instead. PNG files were invented as a free alternative to replace GIF files as the GIF files have proprietary LZW compression algorithm.

Here's one algorithm I can think of -

Step 1 - Get most recent data from DB
Step 2 - Compute MD5 hash of data, or CRC32
Step 3 - Compare it with previous MD5 hash stored, together with timestamp
Step 4 - If hash values differ, new data found
and so on...

Here's a more efficient approach I can think of, if your database supports triggers -

Step 1 Implement database triggers on insert, delete and updates
Step 2 Update the modified flag in a user defined table, say, DATABASE_STATUS, that has two columns, modified_flag and last_modify_time.
Step 3 CGI script checks for the MODIFIED_FLAG in the database
Step 4 Generate new excel & PNG image if necessary by looking at the timestamp and modified_flag.
Step 5 Clear the modified_flag, and set the last_modify_time.


In reply to Re: Strategies for temporary image files in CGI by Roger
in thread Strategies for temporary image files in CGI by Itatsumaki

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