doc.FAQ.WhatDoesMaxLongDataLengthDo

"Max Long Data Length" controls the maximum length of SQL LONGVARCHAR and SQL_LONGVARBINARY data returned when deferred fetching of long data is off. When off, this setting limits the amount of memory which must be allocated for a dataset cell to hold the retrieved value - the value is truncated to this length. The default limit is 60000 bytes.

When deferred fetching is enabled, the complete SQL LONGVARCHAR or SQL_LONGVARBINARY value can be fetched. Note that any value set via SQLSetStmtAttr (SQL_ATTR_MAX_LENGTH) takes precedence over the 'Max Long Data Length' value.