Line data Source code
1 : // Copyright 2018 The LevelDB-Go and Pebble Authors. All rights reserved. Use
2 : // of this source code is governed by a BSD-style license that can be found in
3 : // the LICENSE file.
4 :
5 : package rowblk
6 :
7 : import (
8 : "bytes"
9 : "context"
10 : "fmt"
11 : "os"
12 : "sync"
13 :
14 : "github.com/cockroachdb/pebble/internal/base"
15 : "github.com/cockroachdb/pebble/internal/invariants"
16 : "github.com/cockroachdb/pebble/internal/keyspan"
17 : "github.com/cockroachdb/pebble/internal/rangedel"
18 : "github.com/cockroachdb/pebble/internal/rangekey"
19 : "github.com/cockroachdb/pebble/internal/treeprinter"
20 : "github.com/cockroachdb/pebble/sstable/block"
21 : )
22 :
23 : // fragmentIter wraps an Iter, implementing the keyspan.FragmentIterator
24 : // interface. It's used for reading range deletion and range key blocks.
25 : //
26 : // Range deletions and range keys are fragmented before they're persisted to the
27 : // block. Overlapping fragments have identical bounds. The fragmentIter gathers
28 : // all the fragments with identical bounds within a block and returns a single
29 : // keyspan.Span describing all the keys defined over the span.
30 : //
31 : // # Memory lifetime
32 : //
33 : // A Span returned by fragmentIter is only guaranteed to be stable until the
34 : // next fragmentIter iteration positioning method. A Span's Keys slice may be
35 : // reused, so the user must not assume it's stable.
36 : //
37 : // Blocks holding range deletions and range keys are configured to use a restart
38 : // interval of 1. This provides key stability. The caller may treat the various
39 : // byte slices (start, end, suffix, value) as stable for the lifetime of the
40 : // iterator.
41 : type fragmentIter struct {
42 : suffixCmp base.CompareRangeSuffixes
43 : blockIter Iter
44 : keyBuf [2]keyspan.Key
45 : span keyspan.Span
46 : dir int8
47 :
48 : // fileNum is used for logging/debugging.
49 : fileNum base.DiskFileNum
50 :
51 : syntheticPrefixAndSuffix block.SyntheticPrefixAndSuffix
52 : // startKeyBuf is a buffer that is reused to store the start key of the span
53 : // when a synthetic prefix is used.
54 : startKeyBuf []byte
55 : // endKeyBuf is a buffer that is reused to generate the end key of the span
56 : // when a synthetic prefix is set. It always starts with syntheticPrefix.
57 : endKeyBuf []byte
58 :
59 : closeCheck invariants.CloseChecker
60 : }
61 :
62 : var _ keyspan.FragmentIterator = (*fragmentIter)(nil)
63 :
64 : var fragmentBlockIterPool = sync.Pool{
65 2 : New: func() interface{} {
66 2 : i := &fragmentIter{}
67 2 : // Note: this is a no-op if invariants are disabled or race is enabled.
68 2 : invariants.SetFinalizer(i, checkFragmentBlockIterator)
69 2 : return i
70 2 : },
71 : }
72 :
73 : // NewFragmentIter returns a new keyspan iterator that iterates over a block's
74 : // spans.
75 : func NewFragmentIter(
76 : fileNum base.DiskFileNum,
77 : comparer *base.Comparer,
78 : blockHandle block.BufferHandle,
79 : transforms block.FragmentIterTransforms,
80 2 : ) (keyspan.FragmentIterator, error) {
81 2 : i := fragmentBlockIterPool.Get().(*fragmentIter)
82 2 :
83 2 : i.suffixCmp = comparer.CompareRangeSuffixes
84 2 : // Use the i.keyBuf array to back the Keys slice to prevent an allocation
85 2 : // when the spans contain few keys.
86 2 : i.span.Keys = i.keyBuf[:0]
87 2 : i.fileNum = fileNum
88 2 : i.syntheticPrefixAndSuffix = transforms.SyntheticPrefixAndSuffix
89 2 : if transforms.HasSyntheticPrefix() {
90 2 : i.endKeyBuf = append(i.endKeyBuf[:0], transforms.SyntheticPrefix()...)
91 2 : }
92 2 : i.closeCheck = invariants.CloseChecker{}
93 2 :
94 2 : if err := i.blockIter.InitHandle(comparer, blockHandle, block.IterTransforms{
95 2 : SyntheticSeqNum: transforms.SyntheticSeqNum,
96 2 : // We let the blockIter prepend the prefix to span start keys; the fragment
97 2 : // iterator will prepend it for end keys. We could do everything in the
98 2 : // fragment iterator, but we'd have to duplicate the logic for adjusting the
99 2 : // seek key for SeekGE/SeekLT.
100 2 : SyntheticPrefixAndSuffix: transforms.SyntheticPrefixAndSuffix.RemoveSuffix(),
101 2 : // It's okay for HideObsoletePoints to be false here, even for shared
102 2 : // ingested sstables. This is because rangedels do not apply to points in
103 2 : // the same sstable at the same sequence number anyway, so exposing obsolete
104 2 : // rangedels is harmless.
105 2 : HideObsoletePoints: false,
106 2 : }); err != nil {
107 0 : i.Close()
108 0 : return nil, err
109 0 : }
110 2 : return i, nil
111 : }
112 :
113 : // initSpan initializes the span with a single fragment.
114 : //
115 : // Note that the span start and end keys and range key contents are aliased to
116 : // the key or value when we don't have a synthetic prefix. This is ok because
117 : // the range del/key block doesn't use prefix compression, so the key/value will
118 : // be pointing directly into the buffer data.
119 2 : func (i *fragmentIter) initSpan(ik base.InternalKey, internalValue []byte) error {
120 2 : if ik.Kind() == base.InternalKeyKindRangeDelete {
121 2 : i.span = rangedel.Decode(ik, internalValue, i.span.Keys[:0])
122 2 : } else {
123 2 : var err error
124 2 : i.span, err = rangekey.Decode(ik, internalValue, i.span.Keys[:0])
125 2 : if err != nil {
126 0 : return err
127 0 : }
128 : }
129 : // When synthetic prefix is used in the blockIter, the keys cannot be used
130 : // across multiple blockIter operations; we have to make a copy in this case.
131 2 : if i.syntheticPrefixAndSuffix.HasPrefix() || invariants.Sometimes(10) {
132 2 : i.startKeyBuf = append(i.startKeyBuf[:0], i.span.Start...)
133 2 : i.span.Start = i.startKeyBuf
134 2 : }
135 2 : return nil
136 : }
137 :
138 : // addToSpan adds a fragment to the existing span. The fragment must be for the
139 : // same start/end keys.
140 : func (i *fragmentIter) addToSpan(
141 : cmp base.Compare, ik base.InternalKey, internalValue []byte,
142 2 : ) error {
143 2 : var err error
144 2 : if ik.Kind() == base.InternalKeyKindRangeDelete {
145 2 : err = rangedel.DecodeIntoSpan(cmp, ik, internalValue, &i.span)
146 2 : } else {
147 2 : err = rangekey.DecodeIntoSpan(cmp, ik, internalValue, &i.span)
148 2 : }
149 2 : return err
150 : }
151 :
152 : // applySpanTransforms applies changes to the span that we decoded, if
153 : // appropriate.
154 2 : func (i *fragmentIter) applySpanTransforms() error {
155 2 : if i.syntheticPrefixAndSuffix.HasPrefix() || invariants.Sometimes(10) {
156 2 : syntheticPrefix := i.syntheticPrefixAndSuffix.Prefix()
157 2 : // We have to make a copy of the start key because it will not stay valid
158 2 : // across multiple blockIter operations.
159 2 : i.startKeyBuf = append(i.startKeyBuf[:0], i.span.Start...)
160 2 : i.span.Start = i.startKeyBuf
161 2 : if invariants.Enabled && !bytes.Equal(syntheticPrefix, i.endKeyBuf[:len(syntheticPrefix)]) {
162 0 : panic("pebble: invariant violation: synthetic prefix mismatch")
163 : }
164 2 : i.endKeyBuf = append(i.endKeyBuf[:len(syntheticPrefix)], i.span.End...)
165 2 : i.span.End = i.endKeyBuf
166 : }
167 :
168 2 : if i.syntheticPrefixAndSuffix.HasSuffix() {
169 1 : syntheticSuffix := i.syntheticPrefixAndSuffix.Suffix()
170 1 : for keyIdx := range i.span.Keys {
171 1 : k := &i.span.Keys[keyIdx]
172 1 :
173 1 : switch k.Kind() {
174 1 : case base.InternalKeyKindRangeKeySet:
175 1 : if len(k.Suffix) > 0 {
176 1 : if invariants.Enabled && i.suffixCmp(syntheticSuffix, k.Suffix) >= 0 {
177 1 : return base.AssertionFailedf("synthetic suffix %q >= RangeKeySet suffix %q",
178 1 : syntheticSuffix, k.Suffix)
179 1 : }
180 1 : k.Suffix = syntheticSuffix
181 : }
182 1 : case base.InternalKeyKindRangeKeyDelete:
183 : // Nothing to do.
184 1 : default:
185 1 : return base.AssertionFailedf("synthetic suffix not supported with key kind %s", k.Kind())
186 : }
187 : }
188 : }
189 2 : return nil
190 : }
191 :
192 : // gatherForward gathers internal keys with identical bounds. Keys defined over
193 : // spans of the keyspace are fragmented such that any overlapping key spans have
194 : // identical bounds. When these spans are persisted to a range deletion or range
195 : // key block, they may be persisted as multiple internal keys in order to encode
196 : // multiple sequence numbers or key kinds.
197 : //
198 : // gatherForward iterates forward, re-combining the fragmented internal keys to
199 : // reconstruct a keyspan.Span that holds all the keys defined over the span.
200 2 : func (i *fragmentIter) gatherForward(kv *base.InternalKV) (*keyspan.Span, error) {
201 2 : i.span = keyspan.Span{}
202 2 : if kv == nil || !i.blockIter.Valid() {
203 2 : return nil, nil
204 2 : }
205 : // Use the i.keyBuf array to back the Keys slice to prevent an allocation
206 : // when a span contains few keys.
207 2 : i.span.Keys = i.keyBuf[:0]
208 2 :
209 2 : // Decode the span's end key and individual keys from the value.
210 2 : if err := i.initSpan(kv.K, kv.InPlaceValue()); err != nil {
211 0 : return nil, err
212 0 : }
213 :
214 : // There might exist additional internal keys with identical bounds encoded
215 : // within the block. Iterate forward, accumulating all the keys with
216 : // identical bounds to s.
217 :
218 : // Overlapping fragments are required to have exactly equal start and
219 : // end bounds.
220 2 : for kv = i.blockIter.Next(); kv != nil && i.blockIter.cmp(kv.K.UserKey, i.span.Start) == 0; kv = i.blockIter.Next() {
221 2 : if err := i.addToSpan(i.blockIter.cmp, kv.K, kv.InPlaceValue()); err != nil {
222 0 : return nil, err
223 0 : }
224 : }
225 2 : if err := i.applySpanTransforms(); err != nil {
226 0 : return nil, err
227 0 : }
228 :
229 : // Apply a consistent ordering.
230 2 : keyspan.SortKeysByTrailer(i.span.Keys)
231 2 :
232 2 : // i.blockIter is positioned over the first internal key for the next span.
233 2 : return &i.span, nil
234 : }
235 :
236 : // gatherBackward gathers internal keys with identical bounds. Keys defined over
237 : // spans of the keyspace are fragmented such that any overlapping key spans have
238 : // identical bounds. When these spans are persisted to a range deletion or range
239 : // key block, they may be persisted as multiple internal keys in order to encode
240 : // multiple sequence numbers or key kinds.
241 : //
242 : // gatherBackward iterates backwards, re-combining the fragmented internal keys
243 : // to reconstruct a keyspan.Span that holds all the keys defined over the span.
244 2 : func (i *fragmentIter) gatherBackward(kv *base.InternalKV) (*keyspan.Span, error) {
245 2 : i.span = keyspan.Span{}
246 2 : if kv == nil || !i.blockIter.Valid() {
247 2 : return nil, nil
248 2 : }
249 :
250 : // Decode the span's end key and individual keys from the value.
251 2 : if err := i.initSpan(kv.K, kv.InPlaceValue()); err != nil {
252 0 : return nil, err
253 0 : }
254 :
255 : // There might exist additional internal keys with identical bounds encoded
256 : // within the block. Iterate backward, accumulating all the keys with
257 : // identical bounds to s.
258 : //
259 : // Overlapping fragments are required to have exactly equal start and
260 : // end bounds.
261 2 : for kv = i.blockIter.Prev(); kv != nil && i.blockIter.cmp(kv.K.UserKey, i.span.Start) == 0; kv = i.blockIter.Prev() {
262 2 : if err := i.addToSpan(i.blockIter.cmp, kv.K, kv.InPlaceValue()); err != nil {
263 0 : return nil, err
264 0 : }
265 : }
266 : // i.blockIter is positioned over the last internal key for the previous
267 : // span.
268 :
269 : // Apply a consistent ordering.
270 2 : keyspan.SortKeysByTrailer(i.span.Keys)
271 2 :
272 2 : i.applySpanTransforms()
273 2 : return &i.span, nil
274 : }
275 :
276 : // SetContext is part of the FragmentIterator interface.
277 0 : func (i *fragmentIter) SetContext(ctx context.Context) {}
278 :
279 : // Close implements (keyspan.FragmentIterator).Close.
280 2 : func (i *fragmentIter) Close() {
281 2 : i.blockIter.Close()
282 2 : i.closeCheck.Close()
283 2 :
284 2 : if invariants.Sometimes(25) {
285 2 : // In invariants mode, sometimes don't add the object to the pool so that we
286 2 : // can check for double closes that take longer than the object stays in the
287 2 : // pool.
288 2 : return
289 2 : }
290 2 : i.span = keyspan.Span{}
291 2 : i.dir = 0
292 2 : i.fileNum = 0
293 2 : i.syntheticPrefixAndSuffix = block.SyntheticPrefixAndSuffix{}
294 2 : i.startKeyBuf = i.startKeyBuf[:0]
295 2 : i.endKeyBuf = i.endKeyBuf[:0]
296 2 : fragmentBlockIterPool.Put(i)
297 : }
298 :
299 : // First implements (keyspan.FragmentIterator).First
300 2 : func (i *fragmentIter) First() (*keyspan.Span, error) {
301 2 : i.dir = +1
302 2 : return i.gatherForward(i.blockIter.First())
303 2 : }
304 :
305 : // Last implements (keyspan.FragmentIterator).Last.
306 2 : func (i *fragmentIter) Last() (*keyspan.Span, error) {
307 2 : i.dir = -1
308 2 : return i.gatherBackward(i.blockIter.Last())
309 2 : }
310 :
311 : // Next implements (keyspan.FragmentIterator).Next.
312 2 : func (i *fragmentIter) Next() (*keyspan.Span, error) {
313 2 : switch {
314 2 : case i.dir == -1 && !i.span.Valid():
315 2 : // Switching directions.
316 2 : //
317 2 : // i.blockIter is exhausted, before the first key. Move onto the first.
318 2 : i.blockIter.First()
319 2 : i.dir = +1
320 2 : case i.dir == -1 && i.span.Valid():
321 2 : // Switching directions.
322 2 : //
323 2 : // i.blockIter is currently positioned over the last internal key for
324 2 : // the previous span. Next it once to move to the first internal key
325 2 : // that makes up the current span, and gatherForwaad to land on the
326 2 : // first internal key making up the next span.
327 2 : //
328 2 : // In the diagram below, if the last span returned to the user during
329 2 : // reverse iteration was [b,c), i.blockIter is currently positioned at
330 2 : // [a,b). The block iter must be positioned over [d,e) to gather the
331 2 : // next span's fragments.
332 2 : //
333 2 : // ... [a,b) [b,c) [b,c) [b,c) [d,e) ...
334 2 : // ^ ^
335 2 : // i.blockIter want
336 2 : if x, err := i.gatherForward(i.blockIter.Next()); err != nil {
337 0 : return nil, err
338 2 : } else if invariants.Enabled && !x.Valid() {
339 0 : panic("pebble: invariant violation: next entry unexpectedly invalid")
340 : }
341 2 : i.dir = +1
342 : }
343 : // We know that this blockIter has in-place values.
344 2 : return i.gatherForward(i.blockIter.KV())
345 : }
346 :
347 : // Prev implements (keyspan.FragmentIterator).Prev.
348 2 : func (i *fragmentIter) Prev() (*keyspan.Span, error) {
349 2 : switch {
350 2 : case i.dir == +1 && !i.span.Valid():
351 2 : // Switching directions.
352 2 : //
353 2 : // i.blockIter is exhausted, after the last key. Move onto the last.
354 2 : i.blockIter.Last()
355 2 : i.dir = -1
356 2 : case i.dir == +1 && i.span.Valid():
357 2 : // Switching directions.
358 2 : //
359 2 : // i.blockIter is currently positioned over the first internal key for
360 2 : // the next span. Prev it once to move to the last internal key that
361 2 : // makes up the current span, and gatherBackward to land on the last
362 2 : // internal key making up the previous span.
363 2 : //
364 2 : // In the diagram below, if the last span returned to the user during
365 2 : // forward iteration was [b,c), i.blockIter is currently positioned at
366 2 : // [d,e). The block iter must be positioned over [a,b) to gather the
367 2 : // previous span's fragments.
368 2 : //
369 2 : // ... [a,b) [b,c) [b,c) [b,c) [d,e) ...
370 2 : // ^ ^
371 2 : // want i.blockIter
372 2 : if x, err := i.gatherBackward(i.blockIter.Prev()); err != nil {
373 0 : return nil, err
374 2 : } else if invariants.Enabled && !x.Valid() {
375 0 : panic("pebble: invariant violation: previous entry unexpectedly invalid")
376 : }
377 2 : i.dir = -1
378 : }
379 : // We know that this blockIter has in-place values.
380 2 : return i.gatherBackward(i.blockIter.KV())
381 : }
382 :
383 : // SeekGE implements (keyspan.FragmentIterator).SeekGE.
384 2 : func (i *fragmentIter) SeekGE(k []byte) (*keyspan.Span, error) {
385 2 : if s, err := i.SeekLT(k); err != nil {
386 0 : return nil, err
387 2 : } else if s != nil && i.blockIter.cmp(k, s.End) < 0 {
388 2 : return s, nil
389 2 : }
390 : // TODO(jackson): If the above i.SeekLT(k) discovers a span but the span
391 : // doesn't meet the k < s.End comparison, then there's no need for the
392 : // SeekLT to gatherBackward.
393 2 : return i.Next()
394 : }
395 :
396 : // SeekLT implements (keyspan.FragmentIterator).SeekLT.
397 2 : func (i *fragmentIter) SeekLT(k []byte) (*keyspan.Span, error) {
398 2 : i.dir = -1
399 2 : return i.gatherBackward(i.blockIter.SeekLT(k, base.SeekLTFlagsNone))
400 2 : }
401 :
402 : // String implements fmt.Stringer.
403 0 : func (i *fragmentIter) String() string {
404 0 : return "fragment-block-iter"
405 0 : }
406 :
407 : // WrapChildren implements FragmentIterator.
408 0 : func (i *fragmentIter) WrapChildren(wrap keyspan.WrapFn) {}
409 :
410 : // DebugTree is part of the FragmentIterator interface.
411 0 : func (i *fragmentIter) DebugTree(tp treeprinter.Node) {
412 0 : tp.Childf("%T(%p) fileNum=%s", i, i, i.fileNum)
413 0 : }
414 :
415 2 : func checkFragmentBlockIterator(obj interface{}) {
416 2 : i := obj.(*fragmentIter)
417 2 : if h := i.blockIter.Handle(); h.Valid() {
418 0 : fmt.Fprintf(os.Stderr, "fragmentBlockIter.blockIter.handle is not nil: %#v\n", h)
419 0 : os.Exit(1)
420 0 : }
421 : }
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