The following bug has been logged online:

Bug reference: 1362
Logged by:
Email address: vrs0401 (AT) gmail (DOT) com
PostgreSQL version: 7.4.6
Operating system: linux
Description: Storing large object like 35mb files.
Details:

There is problem how to store large files in postgres.Which datatypes
available for storing large file like 35MB.

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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match