Dataset Memory Tag loses data after gateway stop/start


I have a memory tag of 720 rows and 7 columns, [720R x 7C].

When we stop the gateway and start it back up again this memory tag is cut down to 535 rows and 7 columns, [535R x 7C].

This is a big issue and would like to know if this has to do with a limit on the memory tag or if it’s a bug?


It might have something to do with a limit on the size of a column in the internal DB - is there an error in the gateway logs around the same time you try to write the large dataset?

Yes, I get a really long error at Gateway Startup. Its first part looks like the picture below. The rest of the error message appears to be the data within the dataset.

Right, so this issue is known and currently being tracked. It looks like it should be addressed in Ignition 7.8.5.

Is there a size limit for a memory tag set to datatype dataset?

Yes, but not in # of rows or columns, but in the # of bytes in its serialized form. That has to fit in a blob column in the internal database. Newer installs initialize that to a large column, IIRC, but older stuff might still have narrow columns. If you are having trouble with this, support should be able to help.

Do we know what this limit of size is? For a quick project I tried to save images (less than 200KB) into a Dataset tag to dynamically populate an image component (or paintable canvas). Sure enough once you restart the gateway, those tags are cleared or they have an error where the gateway was unable to restore the value from its internal database. Then, I noticed in Ignition 8 there is a new Binary data type and thought this would be the savior…sadly, it also is unable to retain the data after a gateway restart. I had no choice but to add all images into Ignitions built-in Image Management. (Note that for this project I did not have access to use a database…otherwise I would have saved it in a blob format).