From LimeSurvey Manual
Note: 'Survey size' refers to the maximum number of questions (and answers) in your survey - don't confuse this with the number of replies on your survey (there is no limitation on that). Theoretically there would also be no limit on the maximum number of questions/answers in LimeSurvey. But the database engine you are using has several limits. The most important one is the limit on the number of fields(columns) in the result table.
- MySQL ISAM: The sum of the lengths of the VARCHAR and CHAR columns in a table may be up to 64KB.
- MySQL InnoDB: Maximum number of 1000 columns
- MS SQL Server 2000: Maximum number of 1024 columns
- Postgres: Maximum number of 250-1600 columns depending on column types. The maximum number of columns can be quadrupled by increasing the default block size to 32k. See Installation FAQ and PostgreSQL FAQ.