colblk: implement HideObsoletePoints in DataBlockIter

[RaduBerinde]

colblk: minor benchmark refactoring

Adding a "short" version for the iterator benchmarks. We will add
combinations of various transforms with these selected configs.

We also slightly improve the benchmark naming.

colblk: implement HideObsoletePoints in DataBlockIter

Benchmark for the no-transform path before/after:

name                                                                                old time/op    new time/op    delta
CockroachDataBlockIterShort/AlphaLen=8,Prefix=8,Shared=4,ValueLen=8/Next-10           12.2ns ± 0%    12.5ns ± 3%  +2.38%  (p=0.008 n=5+5)
CockroachDataBlockIterShort/AlphaLen=8,Prefix=8,Shared=4,ValueLen=8/SeekGE-10          113ns ± 0%     114ns ± 0%  +0.80%  (p=0.008 n=5+5)
CockroachDataBlockIterShort/AlphaLen=8,Prefix=128,Shared=64,ValueLen=128/Next-10      10.1ns ± 0%    10.3ns ± 0%  +2.30%  (p=0.016 n=5+4)
CockroachDataBlockIterShort/AlphaLen=8,Prefix=128,Shared=64,ValueLen=128/SeekGE-10    89.4ns ± 0%    90.3ns ± 0%  +1.08%  (p=0.008 n=5+5)

Transforms benchmarks:

name                                                                                                  time/op
CockroachDataBlockIterTransforms/AlphaLen=8,Prefix=8,Shared=4,ValueLen=8/Next-10                      12.3ns ± 1%
CockroachDataBlockIterTransforms/AlphaLen=8,Prefix=8,Shared=4,ValueLen=8/SeekGE-10                     113ns ± 0%
CockroachDataBlockIterTransforms/AlphaLen=8,Prefix=8,Shared=4,ValueLen=8,SynthSeqNum/Next-10          12.5ns ± 0%
CockroachDataBlockIterTransforms/AlphaLen=8,Prefix=8,Shared=4,ValueLen=8,SynthSeqNum/SeekGE-10         114ns ± 1%
CockroachDataBlockIterTransforms/AlphaLen=8,Prefix=8,Shared=4,ValueLen=8,HideObsolete/Next-10         13.0ns ± 1%
CockroachDataBlockIterTransforms/AlphaLen=8,Prefix=8,Shared=4,ValueLen=8,HideObsolete/SeekGE-10        117ns ± 1%
CockroachDataBlockIterTransforms/AlphaLen=8,Prefix=128,Shared=64,ValueLen=128/Next-10                 10.3ns ± 0%
CockroachDataBlockIterTransforms/AlphaLen=8,Prefix=128,Shared=64,ValueLen=128/SeekGE-10               90.5ns ± 1%
CockroachDataBlockIterTransforms/AlphaLen=8,Prefix=128,Shared=64,ValueLen=128,SynthSeqNum/Next-10     10.5ns ± 0%
CockroachDataBlockIterTransforms/AlphaLen=8,Prefix=128,Shared=64,ValueLen=128,SynthSeqNum/SeekGE-10   90.9ns ± 1%
CockroachDataBlockIterTransforms/AlphaLen=8,Prefix=128,Shared=64,ValueLen=128,HideObsolete/Next-10    10.8ns ± 0%
CockroachDataBlockIterTransforms/AlphaLen=8,Prefix=128,Shared=64,ValueLen=128,HideObsolete/SeekGE-10  93.9ns ± 0%

[cockroach-teamcity]

This change is 

[jbowens]

Reviewed 2 of 5 files at r1, all commit messages.
Reviewable status: 2 of 5 files reviewed, 3 unresolved discussions (waiting on @RaduBerinde)

---

sstable/colblk/data_block.go line 805 at r1 (raw file):

			i.nextObsoletePoint = i.r.isObsolete.SeekSetBitGE(i.row)
		} else {
			i.nextObsoletePoint = i.maxRow + 1

if i.row == i.maxRow, isn't it possible for i.r.isObsolete.At(i.row) == true, in which case we want to set i.nextObsoletePoint = i.row?

---

sstable/colblk/data_block.go line 806 at r1 (raw file):

		} else {
			i.nextObsoletePoint = i.maxRow + 1
		}

would it make things cleaner if Seek[Unset|Set]BitGE(n) where n >= BitmapBuilder.bitCount was defined as BitmapBuilder.bitCount? so that even if i.row == i.maxRow+1, we can blindly call Seek[Unset|Set]BitGE?

---

sstable/colblk/data_block.go line 963 at r1 (raw file):

//gcassert:inline
func (i *DataBlockIter) atObsoletePointForward() bool {
	return i.row == i.nextObsoletePoint && i.row <= i.maxRow

is there an invariant that if i.row != i.nextObsoletePoint, i.row < i.nextObsoletePoint? should we assert as much?

[RaduBerinde]

TFTR!

Reviewable status: 2 of 5 files reviewed, 3 unresolved discussions (waiting on @jbowens)

---

sstable/colblk/data_block.go line 805 at r1 (raw file):

Previously, jbowens (Jackson Owens) wrote…

if i.row == i.maxRow, isn't it possible for i.r.isObsolete.At(i.row) == true, in which case we want to set i.nextObsoletePoint = i.row?

Nice catch, added a test for this case.

---

sstable/colblk/data_block.go line 806 at r1 (raw file):

Previously, jbowens (Jackson Owens) wrote…

would it make things cleaner if Seek[Unset|Set]BitGE(n) where n >= BitmapBuilder.bitCount was defined as BitmapBuilder.bitCount? so that even if i.row == i.maxRow+1, we can blindly call Seek[Unset|Set]BitGE?

I was afraid it might cause other paths (like prefixChanged.SeekSetBitGE() to regress. I did it in a local method though, much better.

---

sstable/colblk/data_block.go line 963 at r1 (raw file):

Previously, jbowens (Jackson Owens) wrote…

is there an invariant that if i.row != i.nextObsoletePoint, i.row < i.nextObsoletePoint? should we assert as much?

Yes, added an assert here (I was afraid it would mess with the gcassert:inline check, but then I realized that the build for the check doesn't use the invariants tag).

[jbowens]

Reviewed 2 of 2 files at r2, all commit messages.
Reviewable status: 4 of 5 files reviewed, all discussions resolved

[jbowens]

--- FAIL: TestLint (42.48s)
    --- FAIL: TestLint/TestGCAssert (10.61s)
        lint_test.go:129: See /tmp/gcassert-1156708372.log for full output.
        lint_test.go:132: 
            sstable/colblk/data_block.go:802:	i.setNextObsoletePoint(): call was not inlined
        lint_test.go:132: 
            sstable/colblk/data_block.go:831:	i.setNextObsoletePoint(): call was not inlined
        lint_test.go:132: 
            sstable/colblk/data_block.go:846:	i.setNextObsoletePoint(): call was not inlined
        lint_test.go:132: 
            sstable/colblk/data_block.go:931:	i.setNextObsoletePoint(): call was not inlined
        lint_test.go:132: 
            sstable/colblk/data_block.go:979:	i.setNextObsoletePoint(): call was not inlined

:'(

[RaduBerinde]

So strange, SeekBitGE is not inlined, so how can just an if and a function call be too much to inline? Full logs show setNextObsoletePoint: function too complex: cost 81 exceeds budget 80

[RaduBerinde]

Ok, moved the check to SeekBitGE and verified that it didn't affect the normal benchmarks:

name                                                                                old time/op    new time/op    delta
CockroachDataBlockIterShort/AlphaLen=8,Prefix=8,Shared=4,ValueLen=8/Next-10           12.1ns ± 0%    11.9ns ± 1%  -1.55%  (p=0.000 n=8+8)
CockroachDataBlockIterShort/AlphaLen=8,Prefix=8,Shared=4,ValueLen=8/SeekGE-10          113ns ± 0%     113ns ± 0%    ~     (p=0.631 n=8+8)
CockroachDataBlockIterShort/AlphaLen=8,Prefix=128,Shared=64,ValueLen=128/Next-10      10.1ns ± 0%    10.2ns ± 0%  +0.75%  (p=0.000 n=8+7)
CockroachDataBlockIterShort/AlphaLen=8,Prefix=128,Shared=64,ValueLen=128/SeekGE-10    89.6ns ± 0%    91.0ns ± 1%  +1.58%  (p=0.000 n=7+8)

[jbowens]

Reviewable status: 3 of 6 files reviewed, all discussions resolved

[RaduBerinde]

TFTR!