This patch optimizes the md5_text() function (which is used to
implement the md5() SQL-level function). The old code did the
1. de-toast the datum
2. convert it to a cstring via textout()
3. get the length of the cstring via strlen()
Since we are treating the datum context as a blob of binary data,
the latter two steps are unnecessary. Once the data has been
detoasted, we can just use it as-is, and derive its length from
the varlena metadata.
This patch improves some run-of-the-mill md5() computations by
just under 10% in my limited tests, and passes the regression tests.
I also noticed that md5_text() wasn't checking the return value
of md5_hash(); encountering OOM at precisely the right moment
could result in returning a random md5 hash. This patch corrects
that. A better fix would be to make md5_hash() only return on
success (and/or allocate via palloc()), but since it's used in
the frontend as well I don't see an easy way to do that.
md5.c (r1.27 -> r1.28)
varlena.c (r1.118 -> r1.119)
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