gaodayue commented on issue #1684: [Proposal] Bitmap Index File Format for V2 segment URL: https://github.com/apache/incubator-doris/issues/1684#issuecomment-526063742 @imay thanks for the comments. > If we support other type of index, for example B+Tree, do we need to store all index type in one index file? No we don't. Different types of index will have different structure and metadata, I don't think it's a good idea write them into a single file. > I think we should keep file immutable, so I don't agree with the second option to add new index. What about having multiple index files for one data file? If we add a new index, we can create a new index file for it. and we can merge all index files into one index file when we do compaction. Agree. In this way the I/O cost of adding a new index is minimum, but reader now needs to know what indexes are available for this segment and the place of each index. Where do you think is the best place for such information? Perhaps in RowsetMetaPB? > Now, we store dictionary in two levels, how much data size does this can support? Why not we abstract this to a B-tree which can support multiple layer. here is kudu's implementation which we can reference. Since the dictionary is per segment, it won't be very large. So I think two-level is enough for most dataset. It's also a lot simpler and easier to implement than B-Tree. I think we should first start with the simpler approach and switch to the more complicated approach only when it's proven to be really necessary. Thanks for the link, I'll take a look.
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