Golang Posting.Op方法代碼示例

func addPosting(b *flatbuffers.Builder, p types.Posting) flatbuffers.UOffsetT {
	so := b.CreateByteString(p.Source()) // Do this before posting start.
	var bo flatbuffers.UOffsetT
	if p.ValueLength() > 0 {
		bo = b.CreateByteVector(p.ValueBytes())
	}

	types.PostingStart(b)
	types.PostingAddUid(b, p.Uid())
	if bo > 0 {
		types.PostingAddValue(b, bo)
	}
	types.PostingAddSource(b, so)
	types.PostingAddTs(b, p.Ts())
	types.PostingAddOp(b, p.Op())
	return types.PostingEnd(b)
}

// mutationIndex (mindex) is useful to avoid having to parse the entire
// postinglist upto idx, for every Get(*types.Posting, idx), which has a
// complexity of O(idx). Iteration over N size posting list would this push
// us into O(N^2) territory, without this technique.
//
// Using this technique,
// we can overlay mutation layers over immutable posting list, to allow for
// O(m) lookups, where m = size of mutation list. Obviously, the size of
// mutation list should be much smaller than the size of posting list, except
// in tiny posting lists, where performance wouldn't be such a concern anyways.
//
// Say we have this data:
// Posting List (plist, immutable):
// idx:   0  1  2  3  4  5
// value: 2  5  9 10 13 15
//
// Mutation List (mlist):
// idx:          0   1   2
// value:        7  10  13' // posting uid is 13 but other values vary.
// Op:         SET DEL SET
// Effective:  ADD DEL REP  (REP = replace)
//
// ----------------------------------------------------------------------------
// regenerateIndex would generate these:
// mlayer (layer just above posting list contains only replace instructions)
// idx:          4
// value:       13'
// Op:       	 SET
// Effective:  REP  (REP = replace)
//
// mindex:
// idx:          2   4
// value:        7  10
// moveidx:     -1  +1
// Effective:  ADD DEL
//
// Now, let's see how the access would work:
// idx: get --> calculation [idx, served from, value]
// idx: 0 --> 0   [0, plist, 2]
// idx: 1 --> 1   [1, plist, 5]
// idx: 2 --> ADD from mindex
//        -->     [2, mindex, 7] // also has moveidx = -1
// idx: 3 --> 3 + moveidx=-1 = 2 [2, plist, 9]
// idx: 4 --> DEL from mindex
//        --> 4 + moveidx=-1 + moveidx=+1 = 4 [4, mlayer, 13']
// idx: 5 --> 5 + moveidx=-1 + moveidx=+1 = 5 [5, plist, 15]
//
// Thus we can provide mutation layers over immutable posting list, while
// still ensuring fast lookup access.
//
// NOTE: This function expects the caller to hold a RW Lock.
// Update: With mergeMutation function, we're adding mutations with a cost
// of O(log M + log N), where M = number of previous mutations, and N =
// number of postings in the immutable posting list.
func (l *List) mergeMutation(mp *types.Posting) {
	curUid := mp.Uid()
	pi, puid := l.lePostingIndex(curUid)  // O(log N)
	mi, muid := l.leMutationIndex(curUid) // O(log M)
	inPlist := puid == curUid

	// O(1) follows, but any additions or deletions from mindex would
	// be O(M) due to element shifting. In terms of benchmarks, this performs
	// a LOT better than when I was running O(N + M), re-generating mutation
	// flatbuffers, linked lists etc.
	mlink := new(MutationLink)
	mlink.posting = mp

	if mp.Op() == Del {
		if muid == curUid { // curUid found in mindex.
			if inPlist { // In plist, so replace previous instruction in mindex.
				mlink.moveidx = 1
				mlink.idx = pi + mi
				l.mindex[mi] = mlink

			} else { // Not in plist, so delete previous instruction in mindex.
				l.mdelta -= 1
				l.mindexDeleteAt(mi)
			}

		} else { // curUid not found in mindex.
			if inPlist { // In plist, so insert in mindex.
				mlink.moveidx = 1
				l.mdelta -= 1
				mlink.idx = pi + mi + 1
				l.mindexInsertAt(mlink, mi+1)

			} else {
				// Not found in plist, and not found in mindex. So, ignore.
			}
		}

	} else if mp.Op() == Set {
		if muid == curUid { // curUid found in mindex.
			if inPlist { // In plist, so delete previous instruction, set in mlayer.
				l.mindexDeleteAt(mi)
				l.mlayer[pi] = *mp

			} else { // Not in plist, so replace previous set instruction in mindex.
				// NOTE: This prev instruction couldn't have been a Del instruction.
				mlink.idx = pi + 1 + mi
//.........這裏部分代碼省略.........

func (l *List) updateMutationLayer(mpost *types.Posting) bool {
	l.AssertLock()
	x.AssertTrue(mpost.Op == Set || mpost.Op == Del)

	// First check the mutable layer.
	midx := sort.Search(len(l.mlayer), func(idx int) bool {
		mp := l.mlayer[idx]
		return mpost.Uid <= mp.Uid
	})

	// This block handles the case where mpost.UID is found in mutation layer.
	if midx < len(l.mlayer) && l.mlayer[midx].Uid == mpost.Uid {
		// mp is the posting found in mlayer.
		oldPost := l.mlayer[midx]

		// Note that mpost.Op is either Set or Del, whereas oldPost.Op can be
		// either Set or Del or Add.
		msame := samePosting(oldPost, mpost)
		if msame && ((mpost.Op == Del) == (oldPost.Op == Del)) {
			// This posting has similar content as what is found in mlayer. If the
			// ops are similar, then we do nothing. Note that Add and Set are
			// considered similar, and the second clause is true also when
			// mpost.Op==Add and oldPost.Op==Set.
			return false
		}

		if !msame && mpost.Op == Del {
			// Invalid Del as contents do not match.
			return false
		}

		// Here are the remaining cases.
		// Del, Set: Replace with new post.
		// Del, Del: Replace with new post.
		// Set, Del: Replace with new post.
		// Set, Set: Replace with new post.
		// Add, Del: Undo by removing oldPost.
		// Add, Set: Replace with new post. Need to set mpost.Op to Add.
		if oldPost.Op == Add {
			if mpost.Op == Del {
				// Undo old post.
				copy(l.mlayer[midx:], l.mlayer[midx+1:])
				l.mlayer[len(l.mlayer)-1] = nil
				l.mlayer = l.mlayer[:len(l.mlayer)-1]
				return true
			}
			// Add followed by Set is considered an Add. Hence, mutate mpost.Op.
			mpost.Op = Add
		}
		l.mlayer[midx] = mpost
		return true
	}

	// Didn't find it in mutable layer. Now check the immutable layer.
	pl := l.getPostingList(0)
	pidx := sort.Search(len(pl.Postings), func(idx int) bool {
		p := pl.Postings[idx]
		return mpost.Uid <= p.Uid
	})

	var uidFound, psame bool
	if pidx < len(pl.Postings) {
		p := pl.Postings[pidx]
		uidFound = mpost.Uid == p.Uid
		if uidFound {
			psame = samePosting(p, mpost)
		}
	}

	if mpost.Op == Set {
		if psame {
			return false
		}
		if !uidFound {
			// Posting not found in PL. This is considered an Add operation.
			mpost.Op = Add
		}
	} else if !psame { // mpost.Op==Del
		// Either we fail to find UID in immutable PL or contents don't match.
		return false
	}

	// Doesn't match what we already have in immutable layer. So, add to mutable layer.
	if midx >= len(l.mlayer) {
		// Add it at the end.
		l.mlayer = append(l.mlayer, mpost)
		return true
	}

	// Otherwise, add it where midx is pointing to.
	l.mlayer = append(l.mlayer, nil)
	copy(l.mlayer[midx+1:], l.mlayer[midx:])
	l.mlayer[midx] = mpost
	return true
}