Hi Dawei, Thank you so much that you share your opinion about new TsFile! I am very happy to take your suggestions.
You said we can remove TsOffsetArray and directly store the offset of TimeseriesMetaData. I agree with you. It is better than my version. Besides, for the optimization of TimeserieMetaData, I would like to discuss with other people to determine which way is better. Best, Haonan Hou > On Feb 11, 2020, at 5:35 PM, atoiLiu <[email protected]> wrote: > > Hi, > > I’m learning new TsFile in PR [1], but I think TsFileMetaData has a bad > design. > > TsFileMetaData has a TsOffsetArray, TsOffsetArray is record every offset of > TimeseriesMetaData, and use Map<deviceId, int[]> to record startIndex , > endIndex of TsOffsetArray, it’s looks like : > > TsFileMetaData —>{ [0,1,2,3,4,5, ….] [ {deviceId(d0), [0,2] }, {deviceId(d1), > [3,5] }, …. } } > > We can delete TsOffsetArray and store the offsets directly in the > deviceIndexArray, then TsFileMatadata will has a Map<deviceId, List<Long>> to > record . This change will save 4 bytes per device on disk, because every > device just need record the number of offsets and offsets. it’s looks like： > > TsFileMetaData ---> [ {deviceId(d0), [0,1,2] }, {deviceId(d1), [3,4,5] }, … } > > > In addition, TimeSeriesMetaData is an ordered structure on the hard disk, and > the TimeSeriesMetaData for each device is linked together, so TsFileMetaData > does not need to store all offset information, so there two optimization > directions: > > 1. Save startTime , endTime and offset for each TimeSeriesMetaData in > TsFileMetaData. The nice thing about this is that when you read > TsFileMetaData from your hard drive, you can directly do a filter to filter > which TimeSeriesMetaData is not necessary to read. > > > 2. Only save the start TimeSeriesMetaData offset in TsFileMetaData so that > you can loop through it and just need once to seek, it’s looks like : > > TsFileMetaData ---> [ {deviceId(d0), 0 }, {deviceId(d1), 3 }, … } > > > > [1] https://github.com/apache/incubator-iotdb/pull/736 > <https://github.com/apache/incubator-iotdb/pull/736> > > Thanks > > Dawei Liu
