About Management of Extended Data Memory Use (AutoLISP)

Extended data is limited to 16K per entity.

Because the xdata of an entity can be created and maintained by multiple applications, problems can result when the size of the xdata approaches its limit. The following functions can be used to help manage the memory that xdata occupies.

The xdsize function can be slow when reading a large extended data list, so it is not recommended that you call it frequently. A better approach is to use it (in conjunction with xdroom) in an error handler. If a call to entmod fails, you can use xdsize and xdroom to find out whether the call failed because the entity did not have enough room for the xdata.