.

wcfs/wcfs.go

@@ -612,6 +612,7 @@ type BigFile struct {
 //	//
 //	// XXX computationally expensive to start - see "Invalidations to wcfs
 //	// clients are delayed ..." in notes.txt
+//	//go:generate ./gen-δtail I64 int64 zδtail_i64.go
 //	δtail *ΔTailI64 // [](rev↑, []#blk)
 
 	// inflight loadings of ZBigFile from ZODB.

wcfs/zδtail_i64.go

-// Code generated by gen-δtail I64 int64; DO NOT EDIT.
-// (from lab.nexedi.com/kirr/neo/go/zodb @ v1.9-2339-gc2d001e1)
-
-// Copyright (C) 2018-2020  Nexedi SA and Contributors.
-//                          Kirill Smelkov <kirr@nexedi.com>
-//
-// This program is free software: you can Use, Study, Modify and Redistribute
-// it under the terms of the GNU General Public License version 3, or (at your
-// option) any later version, as published by the Free Software Foundation.
-//
-// You can also Link and Combine this program with other software covered by
-// the terms of any of the Free Software licenses or any of the Open Source
-// Initiative approved licenses and Convey the resulting work. Corresponding
-// source of such a combination shall include the source code for all other
-// software used.
-//
-// This program is distributed WITHOUT ANY WARRANTY; without even the implied
-// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
-//
-// See COPYING file for full licensing terms.
-// See https://www.nexedi.com/licensing for rationale and options.
-
-package main
-
-import "lab.nexedi.com/kirr/neo/go/zodb"
-
-// XXX do we really need ΔTailI64 to be exported from zodb?
-// (other users are low level caches + maybe ZEO/NEO -> zplumbing? but then import cycle)
-
-import (
-	"fmt"
-)
-
-// ΔTailI64 represents tail of revisional changes.
-//
-// It semantically consists of
-//
-//	[](rev↑, []id)		; rev ∈ (tail, head]
-//
-// and index
-//
-//	{} id -> max(rev: rev changed id)
-//
-// where
-//
-//	rev          - is ZODB revision,
-//	id           - is an identifier of what has been changed(*), and
-//	(tail, head] - is covered revision range
-//
-// It provides operations to
-//
-//	- append information to the tail about next revision,
-//	- forget information in the tail past specified revision,
-//	- query the tail for slice with rev ∈ (lo, hi],
-//	- query the tail about what is last revision that changed an id,
-//	- query the tail for len and (tail, head].
-//
-// ΔTailI64 is safe to access for multiple-readers / single writer.
-//
-// (*) examples of id:
-//
-//	oid  - ZODB object identifier, when ΔTailI64 represents changes to ZODB objects,
-//	#blk - file block number, when ΔTailI64 represents changes to a file.
-type ΔTailI64 struct {
-	head  zodb.Tid
-	tail  zodb.Tid
-	tailv []ΔRevEntry
-
-	lastRevOf map[int64]zodb.Tid // index for LastRevOf queries
-	// XXX -> lastRevOf = {} oid -> []rev↑ if linear scan in LastRevOf starts to eat cpu
-}
-
-// ΔRevEntry represents information of what have been changed in one revision.
-type ΔRevEntry struct {
-	Rev     zodb.Tid
-	Changev []int64
-}
-
-// NewΔTailI64 creates new ΔTailI64 object.
-//
-// Initial coverage of created ΔTailI64 is (at₀, at₀].
-func NewΔTailI64(at0 zodb.Tid) *ΔTailI64 {
-	return &ΔTailI64{
-		head:      at0,
-		tail:      at0,
-		lastRevOf: make(map[int64]zodb.Tid),
-	}
-}
-
-// Len returns number of revisions.
-func (δtail *ΔTailI64) Len() int {
-	return len(δtail.tailv)
-}
-
-// Data returns slice with δtail data.
-//
-// The caller must not modify returned slice.
-func (δtail *ΔTailI64) Data() /*readonly*/ []ΔRevEntry {
-	return δtail.tailv
-}
-
-// Head returns newest database state for which δtail has history coverage.
-//
-// Head is ↑ on Append, in particular it does not ↓ on Forget even if δtail becomes empty.
-func (δtail *ΔTailI64) Head() zodb.Tid {
-	return δtail.head
-}
-
-// Tail returns lower-bound of database state for which δtail has history coverage.
-//
-// Tail is ↑= on Forget, even if δtail becomes empty.
-func (δtail *ΔTailI64) Tail() zodb.Tid {
-	return δtail.tail
-}
-
-// SliceByRev returns δtail slice of elements with .rev ∈ (low, high].
-//
-// it must be called with the following condition:
-//
-//	tail ≤ low ≤ high ≤ head
-//
-// the caller must not modify returned slice.
-//
-// Note: contrary to regular go slicing, low is exclusive while high is inclusive.
-func (δtail *ΔTailI64) SliceByRev(low, high zodb.Tid) /*readonly*/ []ΔRevEntry {
-	tail := δtail.tail
-	head := δtail.head
-	if !(tail <= low && low <= high && high <= head) {
-		panic(fmt.Sprintf("δtail.Slice: invalid query: (%s, %s];  (tail, head] = (%s, %s]", low, high, tail, head))
-	}
-
-	tailv := δtail.tailv
-
-	// ex (0,0] tail..head = 0..0
-	if len(tailv) == 0 {
-		return tailv
-	}
-
-	// find max j : [j].rev ≤ high		XXX linear scan -> binary search
-	j := len(tailv)-1
-	for ; j >= 0 && tailv[j].Rev > high; j-- {}
-	if j < 0 {
-		return nil // ø
-	}
-
-	// find max i : [i].rev > low		XXX linear scan -> binary search
-	i := j
-	for ; i >= 0 && tailv[i].Rev > low; i-- {}
-	i++
-
-	return tailv[i:j+1]
-}
-
-// XXX add way to extend coverage without appending changed data? (i.e. if a
-// txn did not change file at all) -> but then it is simply .Append(rev, nil)?
-
-// Append appends to δtail information about what have been changed in next revision.
-//
-// rev must be ↑.
-func (δtail *ΔTailI64) Append(rev zodb.Tid, changev []int64) {
-	// check rev↑
-	if δtail.head >= rev {
-		panic(fmt.Sprintf("δtail.Append: rev not ↑: %s -> %s", δtail.head, rev))
-	}
-
-	δtail.head = rev
-	δtail.tailv = append(δtail.tailv, ΔRevEntry{rev, changev})
-	for _, id := range changev {
-		δtail.lastRevOf[id] = rev
-	}
-}
-
-// ForgetPast discards all δtail entries with rev ≤ revCut.
-func (δtail *ΔTailI64) ForgetPast(revCut zodb.Tid) {
-	// revCut ≤ tail: nothing to do; don't let .tail go ↓
-	if revCut <= δtail.tail {
-		return
-	}
-
-	icut := 0
-	for i, δ := range δtail.tailv {
-		rev := δ.Rev
-		if rev > revCut {
-			break
-		}
-		icut = i+1
-
-		// if forgotten revision was last for id, we have to update lastRevOf index
-		for _, id := range δ.Changev {
-			if δtail.lastRevOf[id] == rev {
-				delete(δtail.lastRevOf, id)
-			}
-		}
-	}
-
-	// tailv = tailv[icut:]	  but without
-	// 1) growing underlying storage array indefinitely
-	// 2) keeping underlying storage after forget
-	l := len(δtail.tailv)-icut
-	tailv := make([]ΔRevEntry, l)
-	copy(tailv, δtail.tailv[icut:])
-	δtail.tailv = tailv
-
-	δtail.tail = revCut
-}
-
-// XXX -> RevAt ?
-// LastRevOf tries to return what was the last revision that changed id as of at database state.
-//
-// Depending on current information in δtail it returns either exact result, or
-// an upper-bound estimate for the last id revision, assuming id was changed ≤ at:
-//
-// 1) if δtail does not cover at, at is returned:
-//
-//	# at ∉ [min(rev ∈ δtail), max(rev ∈ δtail)]
-//	LastRevOf(id, at) = at
-//
-// 2) if δtail has an entry corresponding to id change, it gives exactly the
-// last revision that changed id:
-//
-//	# at ∈ [min(rev ∈ δtail), max(rev ∈ δtail)]
-//	# ∃ rev ∈ δtail: rev changed id && rev ≤ at
-//	LastRevOf(id, at) = max(rev: rev changed id && rev ≤ at)
-//
-// 3) if δtail does not contain appropriate record with id - it returns δtail's
-// lower bound as the estimate for the upper bound of the last id revision:
-//
-//	# at ∈ [min(rev ∈ δtail), max(rev ∈ δtail)]
-//	# ∄ rev ∈ δtail: rev changed id && rev ≤ at
-//	LastRevOf(id, at) = min(rev ∈ δtail)
-//
-// On return exact indicates whether returned revision is exactly the last
-// revision of id, or only an upper-bound estimate of it.
-func (δtail *ΔTailI64) LastRevOf(id int64, at zodb.Tid) (_ zodb.Tid, exact bool) {
-	// check if we have no coverage at all
-	l := len(δtail.tailv)
-	if l == 0 {
-		return at, false
-	}
-	revMin := δtail.tailv[0].Rev
-	revMax := δtail.tailv[l-1].Rev
-	if !(revMin <= at && at <= revMax) {
-		return at, false
-	}
-
-	// we have the coverage
-	rev, ok := δtail.lastRevOf[id]
-	if !ok {
-		return δtail.tailv[0].Rev, false
-	}
-
-	if rev <= at {
-		return rev, true
-	}
-
-	// what's in index is after at - scan tailv back to find appropriate entry
-	// XXX linear scan - see .lastRevOf comment.
-	for i := l - 1; i >= 0; i-- {
-		δ := δtail.tailv[i]
-		if δ.Rev > at {
-			continue
-		}
-
-		for _, δid := range δ.Changev {
-			if id == δid {
-				return δ.Rev, true
-			}
-		}
-	}
-
-	// nothing found
-	return δtail.tailv[0].Rev, false
-}

wcfs/δtail.go

-// Copyright (C) 2018-2020  Nexedi SA and Contributors.
-//                          Kirill Smelkov <kirr@nexedi.com>
-//
-// This program is free software: you can Use, Study, Modify and Redistribute
-// it under the terms of the GNU General Public License version 3, or (at your
-// option) any later version, as published by the Free Software Foundation.
-//
-// You can also Link and Combine this program with other software covered by
-// the terms of any of the Free Software licenses or any of the Open Source
-// Initiative approved licenses and Convey the resulting work. Corresponding
-// source of such a combination shall include the source code for all other
-// software used.
-//
-// This program is distributed WITHOUT ANY WARRANTY; without even the implied
-// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
-//
-// See COPYING file for full licensing terms.
-// See https://www.nexedi.com/licensing for rationale and options.
-
-// XXX -> internal/δtail/ ?
-
-package main
-// δtail maintenance
-
-//go:generate ./gen-δtail I64 int64 zδtail_i64.go