This patch optimizes the md5_text() function (which is used to

implement the md5() SQL-level function). The old code did the
following:

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.

2 files changed, 11 insertions, 5 deletions

diff --git a/src/backend/libpq/md5.c b/src/backend/libpq/md5.c
index c0405199f9..8855905e6b 100644
--- a/src/backend/libpq/md5.c
+++ b/src/backend/libpq/md5.c
@@ -289,8 +289,8 @@ bytesToHex(uint8 b[16], char *s)
  *						  characters.  you thus need to provide an array
  *						  of 33 characters, including the trailing '\0'.
  *
- *	RETURNS		  0 on failure (out of memory for internal buffers) or
- *				  non-zero on success.
+ *	RETURNS		  false on failure (out of memory for internal buffers) or
+ *				  true on success.
  *
  *	STANDARDS	  MD5 is described in RFC 1321.
  *
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 66c9a6a16c..d2b674477c 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -2310,16 +2310,22 @@ to_hex64(PG_FUNCTION_ARGS)
 Datum
 md5_text(PG_FUNCTION_ARGS)
 {
-	char	   *buff = PG_TEXT_GET_STR(PG_GETARG_TEXT_P(0));
-	size_t		len = strlen(buff);
+	text	   *in_text = PG_GETARG_TEXT_P(0);
+	size_t		len;
 	char	   *hexsum;
 	text	   *result_text;
 
+	/* Calculate the length of the buffer using varlena metadata */
+	len = VARSIZE(in_text) - VARHDRSZ;
+
 	/* leave room for the terminating '\0' */
 	hexsum = (char *) palloc(MD5_HASH_LEN + 1);
 
 	/* get the hash result */
-	md5_hash((void *) buff, len, hexsum);
+	if (md5_hash(VARDATA(in_text), len, hexsum) == false)
+		ereport(ERROR,
+				(errcode(ERRCODE_OUT_OF_MEMORY),
+				 errmsg("out of memory")));
 
 	/* convert to text and return it */
 	result_text = PG_STR_GET_TEXT(hexsum);