Re: Fillfactor for GIN indexes

On Thu, Jul 9, 2015 at 10:33 PM, Alexander Korotkov wrote:
> [...]

+     /* Caclculate max data size on page according to fillfactor */
s/Caclculate/Calculate

When creating a simple gin index, I am seeing that GinGetMaxDataSize gets called with ginEntryInsert:
  * frame #0: 0x000000010a49d72e postgres`GinGetMaxDataSize(index=0x0000000114168378, isBuild='\x01') + 14 at gindatapage.c:436
    frame #1: 0x000000010a49ecbe postgres`createPostingTree(index=0x0000000114168378, items=0x0000000114a9c038, nitems=35772, buildStats=0x00007fff55787350) + 302 at gindatapage.c:1754
    frame #2: 0x000000010a493423 postgres`buildFreshLeafTuple(ginstate=0x00007fff55784d90, attnum=1, key=2105441, category='\0', items=0x0000000114a9c038, nitem=35772, buildStats=0x00007fff55787350) + 339 at gininsert.c:158
    frame #3: 0x000000010a492f84 postgres`ginEntryInsert(ginstate=0x00007fff55784d90, attnum=1, key=2105441, category='\0', items=0x0000000114a9c038, nitem=35772, buildStats=0x00007fff55787350) + 916 at gininsert.c:228

And as far as I can see GinGetMaxDataSize uses isBuild:
+ int
+ GinGetMaxDataSize(Relation index, bool isBuild)
+ {
+     int fillfactor, result;
+
+     /* Grab option value which affects only index build */
+     if (!isBuild)
However isBuild is not set in this code path, see http://www.postgresql.org/message-id/CAB7nPqSc4VQ9mHKqm_YvAfcTEhO-iUY8SKbXYdnMGnAi1XnPaw@mail.gmail.com where I reported the problem. So this code is somewhat broken, no? I am attaching to this email the patch in question that should be applied on top of Alexander's latest version.

+ #define GIN_MIN_FILLFACTOR            20
+ #define GIN_DEFAULT_FILLFACTOR        90
I am still worrying about using a default fillfactor at 90, as we did a lot of promotion about compression of GIN indexes in 9.4. Feel free to ignore this comment if you think that 90 is a good default. The difference is visibly in order of MBs even for large indexes still, this is changing the default of 9.4 and 9.5.