Everyone in that thread knows what a partial write is. That's why the patch author saw this error message:

    > 2011-07-31 22:13:35 EST postgres postgres [local] LOG: connection authorized: user=postgres database=postgres
    > 2011-07-31 22:13:35 EST ERROR: could not write block 1 of relation global/2671: wrote only 4096 of 8192 bytes
    > 2011-07-31 22:13:35 EST HINT: Check free disk space.
    > 2011-07-31 22:13:35 EST CONTEXT: writing block 1 of relation global/2671
    > 2011-07-31 22:13:35 EST [unknown] [unknown] LOG: connection received: host=[local]

If they didn't know what a partial write was, they wouldn't have identified it specifically as an error case with its own informative error message.

The proposed patch retries rather than throwing an error.