emkornfield commented on a change in pull request #11146: URL: https://github.com/apache/arrow/pull/11146#discussion_r734223970
########## File path: go/parquet/file/column_reader.go ########## @@ -0,0 +1,485 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. + +package file + +import ( + "github.com/apache/arrow/go/arrow/memory" + "github.com/apache/arrow/go/parquet" + "github.com/apache/arrow/go/parquet/internal/encoding" + "github.com/apache/arrow/go/parquet/internal/encryption" + format "github.com/apache/arrow/go/parquet/internal/gen-go/parquet" + "github.com/apache/arrow/go/parquet/internal/utils" + "github.com/apache/arrow/go/parquet/schema" + "golang.org/x/xerrors" +) + +const ( + // 4 MB is the default maximum page header size + defaultMaxPageHeaderSize = 4 * 1024 * 1024 + // 16 KB is the default expected page header size + defaultPageHeaderSize = 16 * 1024 +) + +//go:generate go run ../../arrow/_tools/tmpl/main.go -i -data=../internal/encoding/physical_types.tmpldata column_reader_types.gen.go.tmpl + +func isDictIndexEncoding(e format.Encoding) bool { + return e == format.Encoding_RLE_DICTIONARY || e == format.Encoding_PLAIN_DICTIONARY +} + +// CryptoContext is a context for keeping track of the current methods for decrypting. +// It keeps track of the row group and column numbers along with references to the +// decryptor objects. +type CryptoContext struct { + StartDecryptWithDictionaryPage bool + RowGroupOrdinal int16 + ColumnOrdinal int16 + MetaDecryptor encryption.Decryptor + DataDecryptor encryption.Decryptor +} + +// ColumnChunkReader is the basic interface for all column readers. It will use +// a page reader to read all the pages in a column chunk from a row group. +// +// To actually Read out the column data, you need to convert to the properly +// typed ColumnChunkReader type such as *BooleanColumnReader etc. +// +// Some things to clarify when working with column readers: +// +// "Values" refers to the physical data values in a data page. +// +// This is separate from the number of "rows" in a column and the total number +// of "elements" in a column because null values aren't stored physically in the +// data page but are represented via definition levels, so the number of values +// in a column can be less than the number of rows. +// +// The total number of "elements" in a column also differs because of potential +// repeated fields, where you can have multiple values in the page which +// together make up a single element (such as a list) or depending on the repetition +// level and definition level, could represent an entire null list or just a null +// element inside of a list. +type ColumnChunkReader interface { + // HasNext returns whether there is more data to be read in this column + // and row group. + HasNext() bool + // Type returns the underlying physical type of the column + Type() parquet.Type + // Descriptor returns the column schema container + Descriptor() *schema.Column + // if HasNext returns false because of an error, this will return the error + // it encountered. Otherwise this will be nil if it's just the end of the + // column + Err() error + // Skip buffered values + consumeBufferedValues(int64) + // number of available buffered values that have not been decoded yet + // when this returns 0, you're at the end of a page. + numAvailValues() int64 + // read the definition levels and return the number of definitions, + // and the number of values to be read (number of def levels == maxdef level) + // it also populates the passed in slice which should be sized appropriately. + readDefinitionLevels(levels []int16) (int, int64) + // read the repetition levels and return the number of repetition levels read + // also populates the passed in slice, which should be sized appropriately. + readRepetitionLevels(levels []int16) int + // a column is made up of potentially multiple pages across potentially multiple + // row groups. A PageReader allows looping through the pages in a single row group. + // When moving to another row group for reading, use setPageReader to re-use the + // column reader for reading the pages of the new row group. + pager() PageReader + // set a page reader into the columnreader so it can be reused. + // + // This will clear any current error in the reader but does not + // automatically read the first page of the page reader passed in until + // HasNext which will read in the next page. + setPageReader(PageReader) +} + +type columnChunkReader struct { + descr *schema.Column + rdr PageReader + repetitionDecoder encoding.LevelDecoder + definitionDecoder encoding.LevelDecoder + + curPage Page + curEncoding format.Encoding + curDecoder encoding.TypedDecoder + + // number of currently buffered values in the current page + numBuffered int64 + // the number of values we've decoded so far + numDecoded int64 + mem memory.Allocator + + decoders map[format.Encoding]encoding.TypedDecoder + decoderTraits encoding.DecoderTraits + + // is set when an error is encountered + err error + defLvlBuffer []int16 +} + +// NewColumnReader returns a column reader for the provided column initialized with the given pagereader that will +// provide the pages of data for this column. The type is determined from the column passed in. +func NewColumnReader(descr *schema.Column, pageReader PageReader, mem memory.Allocator) ColumnChunkReader { + base := columnChunkReader{descr: descr, rdr: pageReader, mem: mem, decoders: make(map[format.Encoding]encoding.TypedDecoder)} + switch descr.PhysicalType() { + case parquet.Types.FixedLenByteArray: + base.decoderTraits = &encoding.FixedLenByteArrayDecoderTraits + return &FixedLenByteArrayColumnChunkReader{base} + case parquet.Types.Float: + base.decoderTraits = &encoding.Float32DecoderTraits + return &Float32ColumnChunkReader{base} + case parquet.Types.Double: + base.decoderTraits = &encoding.Float64DecoderTraits + return &Float64ColumnChunkReader{base} + case parquet.Types.ByteArray: + base.decoderTraits = &encoding.ByteArrayDecoderTraits + return &ByteArrayColumnChunkReader{base} + case parquet.Types.Int32: + base.decoderTraits = &encoding.Int32DecoderTraits + return &Int32ColumnChunkReader{base} + case parquet.Types.Int64: + base.decoderTraits = &encoding.Int64DecoderTraits + return &Int64ColumnChunkReader{base} + case parquet.Types.Int96: + base.decoderTraits = &encoding.Int96DecoderTraits + return &Int96ColumnChunkReader{base} + case parquet.Types.Boolean: + base.decoderTraits = &encoding.BooleanDecoderTraits + return &BooleanColumnChunkReader{base} + } + return nil +} + +func (c *columnChunkReader) Err() error { return c.err } +func (c *columnChunkReader) Type() parquet.Type { return c.descr.PhysicalType() } +func (c *columnChunkReader) Descriptor() *schema.Column { return c.descr } +func (c *columnChunkReader) consumeBufferedValues(n int64) { c.numDecoded += n } +func (c *columnChunkReader) numAvailValues() int64 { return c.numBuffered - c.numDecoded } +func (c *columnChunkReader) pager() PageReader { return c.rdr } +func (c *columnChunkReader) setPageReader(rdr PageReader) { + c.rdr, c.err = rdr, nil + c.decoders = make(map[format.Encoding]encoding.TypedDecoder) + c.numBuffered, c.numDecoded = 0, 0 +} + +func (c *columnChunkReader) getDefLvlBuffer(sz int64) []int16 { + if int64(len(c.defLvlBuffer)) < sz { + c.defLvlBuffer = make([]int16, sz) + return c.defLvlBuffer + } + + return c.defLvlBuffer[:sz] +} + +// HasNext returns whether there is more data to be read in this column +// and row group. +func (c *columnChunkReader) HasNext() bool { + if c.numBuffered == 0 || c.numDecoded == c.numBuffered { + return c.readNewPage() && c.numBuffered != 0 + } + return true +} + +func (c *columnChunkReader) configureDict(page *DictionaryPage) error { + enc := page.encoding + if enc == format.Encoding_PLAIN_DICTIONARY || enc == format.Encoding_PLAIN { + enc = format.Encoding_RLE_DICTIONARY + } + + if _, ok := c.decoders[enc]; ok { + return xerrors.New("parquet: column chunk cannot have more than one dictionary.") + } + + switch page.Encoding() { + case format.Encoding_PLAIN, format.Encoding_PLAIN_DICTIONARY: + dict := c.decoderTraits.Decoder(parquet.Encodings.Plain, c.descr, false, c.mem) + dict.SetData(int(page.NumValues()), page.Data()) + + decoder := c.decoderTraits.Decoder(parquet.Encodings.Plain, c.descr, true, c.mem).(encoding.DictDecoder) + decoder.SetDict(dict) + c.decoders[enc] = decoder + default: + return xerrors.New("parquet: dictionary index must be plain encoding") + } + + c.curDecoder = c.decoders[enc] + return nil +} + +// read a new page from the page reader +func (c *columnChunkReader) readNewPage() bool { + for c.rdr.Next() { // keep going until we get a data page + c.curPage = c.rdr.Page() + if c.curPage == nil { + break + } + + var lvlByteLen int64 + switch p := c.curPage.(type) { + case *DictionaryPage: + if err := c.configureDict(p); err != nil { + c.err = err + return false + } + continue + case *DataPageV1: + lvlByteLen, c.err = c.initLevelDecodersV1(p, p.repLvlEncoding, p.defLvlEncoding) + if c.err != nil { + return false + } + case *DataPageV2: + lvlByteLen, c.err = c.initLevelDecodersV2(p) + if c.err != nil { + return false + } + default: + // we can skip non-data pages + continue + } + + c.err = c.initDataDecoder(c.curPage, lvlByteLen) + return c.err == nil + } + c.err = c.rdr.Err() + return false +} + +func (c *columnChunkReader) initLevelDecodersV2(page *DataPageV2) (int64, error) { + c.numBuffered = int64(page.nvals) + c.numDecoded = 0 + buf := page.Data() + totalLvlLen := int64(page.repLvlBytelen) + int64(page.defLvlBytelen) + + if totalLvlLen > int64(len(buf)) { + return totalLvlLen, xerrors.New("parquet: data page too small for levels (corrupt header?)") + } + + if c.descr.MaxRepetitionLevel() > 0 { + c.repetitionDecoder.SetDataV2(page.repLvlBytelen, c.descr.MaxRepetitionLevel(), int(c.numBuffered), buf) + buf = buf[page.repLvlBytelen:] + } + + if c.descr.MaxDefinitionLevel() > 0 { + c.definitionDecoder.SetDataV2(page.defLvlBytelen, c.descr.MaxDefinitionLevel(), int(c.numBuffered), buf) + } + + return totalLvlLen, nil +} + +func (c *columnChunkReader) initLevelDecodersV1(page *DataPageV1, repLvlEncoding, defLvlEncoding format.Encoding) (int64, error) { + c.numBuffered = int64(page.nvals) + c.numDecoded = 0 + + buf := page.Data() + maxSize := len(buf) + levelsByteLen := int64(0) + + // Data page layout: Repetition Levels - Definition Levels - encoded values. + // Levels are encoded as rle or bit-packed + if c.descr.MaxRepetitionLevel() > 0 { + repBytes, err := c.repetitionDecoder.SetData(parquet.Encoding(repLvlEncoding), c.descr.MaxRepetitionLevel(), int(c.numBuffered), buf) + if err != nil { + return levelsByteLen, err + } + buf = buf[repBytes:] + maxSize -= repBytes + levelsByteLen += int64(repBytes) + } + + if c.descr.MaxDefinitionLevel() > 0 { + defBytes, err := c.definitionDecoder.SetData(parquet.Encoding(defLvlEncoding), c.descr.MaxDefinitionLevel(), int(c.numBuffered), buf) + if err != nil { + return levelsByteLen, err + } + levelsByteLen += int64(defBytes) + maxSize -= defBytes + } + + return levelsByteLen, nil +} + +func (c *columnChunkReader) initDataDecoder(page Page, lvlByteLen int64) error { + buf := page.Data() + if int64(len(buf)) < lvlByteLen { + return xerrors.New("parquet: page smaller than size of encoded levels") + } + + buf = buf[lvlByteLen:] + encoding := page.Encoding() + + if isDictIndexEncoding(encoding) { + encoding = format.Encoding_RLE_DICTIONARY + } + + if decoder, ok := c.decoders[encoding]; ok { + c.curDecoder = decoder + } else { + switch encoding { + case format.Encoding_PLAIN, + format.Encoding_DELTA_BYTE_ARRAY, + format.Encoding_DELTA_LENGTH_BYTE_ARRAY, + format.Encoding_DELTA_BINARY_PACKED: + c.curDecoder = c.decoderTraits.Decoder(parquet.Encoding(encoding), c.descr, false, c.mem) + c.decoders[encoding] = c.curDecoder + case format.Encoding_RLE_DICTIONARY: + return xerrors.New("parquet: dictionary page must be before data page") + case format.Encoding_BYTE_STREAM_SPLIT: + return xerrors.Errorf("parquet: unsupported data encoding %s", encoding) + default: + return xerrors.Errorf("parquet: unknown encoding type %s", encoding) + } + } + + c.curEncoding = encoding + c.curDecoder.SetData(int(c.numBuffered), buf) + return nil +} + +func (c *columnChunkReader) readDefinitionLevels(levels []int16) (int, int64) { Review comment: even those these are private documenting contract helps readers in the futre. same goes for method below. -- This is an automated message from the Apache Git Service. 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