On Apr 9, 2009, at 1:52 AM, Sergiu Dumitriu
wrote:
  Hi devs,
 While trying to fix XWIKI-1480, the following question was raised:  What
 to do with large values placed inside a StringProperty?
 StringProperties are defined to hold at most 255 characters (which are
 actually bytes in mysql). Some databases automatically ignore this
 limit
 (this is the case with hsql, which is the default database for our
 standalone package), while others throw exceptions when trying to
 commit
 the transaction (mysql does this).
 Currently, we don't handle this exception at all, so it bubbles up to
 the UI in the form of a stack trace. XWIKI-1480 is about fixing this
 error.
 What can be done:
 1. Always trim the content to 255 bytes. This is a regression from the
 point of view of hsql users, which will suddenly notice that their  data
 gets truncated.
 2. If the data is larger than 255 bytes, silently ignore this new
 value,
 and continue using the previous one. This is also bad, since users
 won't
 understand why doesn't the value get saved, and is a regression on
 hsql.
 3. Try to use this value, but if an exception is thrown, truncate the
 data and commit again. This fixes the regression part, but might still
 be surprising to users.
 4. Continue as before, but catch the exception and display a nice
 warning message to the user. This looks like the safest approach,
 but it
 fails when manipulating data from outside the UI, like scripts and
 XmlRpc connections.
 So, what is the best approach? 
 Do we have to store string properties in such small types? Would it
 be  detrimental to performances a lot to use a large DB types to
 store  string properties? 
 I for one don't think that making the field larger is a problem. The
 only downside I see is that it will be harder to make an index on it.
 Maybe our sysadmins can say more about how they optimize databases.