Simplify/speed up assertion cross-check in ginCompressPostingList().

tglsfdc · tglsfdc · commit ea7dace2aa21 · 2020-03-07T13:31:17.000-05:00
I noticed while testing some other stuff that the CHECK_ENCODING_ROUNDTRIP
logic in ginCompressPostingList could account for over 50% of the runtime
of an INSERT with a GIN index.  While that's not relevant to production
performance, it's still kind of annoying in a debug build.  Replacing
the loop around short memcmp's with one long memcmp works just as well
and is significantly faster, at least on my machine.
diff --git a/src/backend/access/gin/ginpostinglist.c b/src/backend/access/gin/ginpostinglist.c
@@ -266,11 +266,9 @@ ginCompressPostingList(const ItemPointer ipd, int nipd, int maxsize,
 	{
 		int			ndecoded;
 		ItemPointer tmp = ginPostingListDecode(result, &ndecoded);
-		int			i;
 
 		Assert(ndecoded == totalpacked);
-		for (i = 0; i < ndecoded; i++)
-			Assert(memcmp(&tmp[i], &ipd[i], sizeof(ItemPointerData)) == 0);
+		Assert(memcmp(tmp, ipd, ndecoded * sizeof(ItemPointerData)) == 0);
 		pfree(tmp);
 	}
 #endif

Original file line number	Diff line number	Diff line change
`@@ -266,11 +266,9 @@ ginCompressPostingList(const ItemPointer ipd, int nipd, int maxsize,`
`266`	`266`	`{`
`267`	`267`	`int ndecoded;`
`268`	`268`	`ItemPointer tmp = ginPostingListDecode(result, &ndecoded);`
`269`		`- int i;`
`270`	`269`
`271`	`270`	`Assert(ndecoded == totalpacked);`
`272`		`- for (i = 0; i < ndecoded; i++)`
`273`		`- Assert(memcmp(&tmp[i], &ipd[i], sizeof(ItemPointerData)) == 0);`
	`271`	`+ Assert(memcmp(tmp, ipd, ndecoded * sizeof(ItemPointerData)) == 0);`
`274`	`272`	`pfree(tmp);`
`275`	`273`	`}`
`276`	`274`	`#endif`