Платформа ЦРНП "Мирокод" для разработки проектов
https://git.mirocod.ru
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67 lines
2.5 KiB
67 lines
2.5 KiB
// Copyright (c) 2019 Couchbase, Inc. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// http://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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package zap |
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import ( |
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"fmt" |
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) |
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// LegacyChunkMode was the original chunk mode (always chunk size 1024) |
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// this mode is still used for chunking doc values. |
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var LegacyChunkMode uint32 = 1024 |
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// DefaultChunkMode is the most recent improvement to chunking and should |
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// be used by default. |
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var DefaultChunkMode uint32 = 1026 |
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func getChunkSize(chunkMode uint32, cardinality uint64, maxDocs uint64) (uint64, error) { |
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switch { |
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// any chunkMode <= 1024 will always chunk with chunkSize=chunkMode |
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case chunkMode <= 1024: |
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// legacy chunk size |
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return uint64(chunkMode), nil |
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case chunkMode == 1025: |
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// attempt at simple improvement |
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// theory - the point of chunking is to put a bound on the maximum number of |
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// calls to Next() needed to find a random document. ie, you should be able |
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// to do one jump to the correct chunk, and then walk through at most |
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// chunk-size items |
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// previously 1024 was chosen as the chunk size, but this is particularly |
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// wasteful for low cardinality terms. the observation is that if there |
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// are less than 1024 items, why not put them all in one chunk, |
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// this way you'll still achieve the same goal of visiting at most |
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// chunk-size items. |
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// no attempt is made to tweak any other case |
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if cardinality <= 1024 { |
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return maxDocs, nil |
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} |
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return 1024, nil |
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case chunkMode == 1026: |
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// improve upon the ideas tested in chunkMode 1025 |
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// the observation that the fewest number of dense chunks is the most |
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// desirable layout, given the built-in assumptions of chunking |
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// (that we want to put an upper-bound on the number of items you must |
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// walk over without skipping, currently tuned to 1024) |
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// |
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// 1. compute the number of chunks needed (max 1024/chunk) |
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// 2. convert to chunkSize, dividing into maxDocs |
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numChunks := (cardinality / 1024) + 1 |
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chunkSize := maxDocs / numChunks |
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return chunkSize, nil |
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} |
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return 0, fmt.Errorf("unknown chunk mode %d", chunkMode) |
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}
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