Order chunks for compression by range_start #7148
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RobAtticus
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Previously, when compressing chunks the order was non-deterministic; it was usaully ordered by chunk id, but not guaranteed. And while typically chunk id corresponds with range_start, it is not always so: backfilling chunks can lead to larger chunk ids for older chunks. Generally, it seems preferable to compress chunks oldest to newest. When using the experimental compress_chunk_time_interval option, it is even more so preferable because it allows for the most efficient roll ups. If not, the chunks compressed out of order can "cut off" a rolled up chunk before it was completely full.
RobAtticus
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Did you test this with hypertables with multiple dimensions? |
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I did not, but I'm realizing I want to probably just do it by the primary dimension |
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Is this going to cause even more problems for backilling? Meaning, ordering by range_start will probably make the backfilled chunks be compressed sooner, potentially even while they are being backfilled. This could happen even in current setup but now its guaranteed to be picked up sooner rather than later. Thoughts on doing this ordering only if you are using compress_created_before to avoid said issues? Other than that, I'm OK with this change. |
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Looks like a good change, certainly better than no particular order. Wondering if it would be good to also add an option to do other ordering as a configuration option.
You might also want to consider ordering by all dimensions, to have more determinism with multi-dimensional partitioning.
Previously, when compressing chunks the order was non-deterministic; it was usaully ordered by chunk id, but not guaranteed. And while typically chunk id corresponds with range_start, it is not always so: backfilling chunks can lead to larger chunk ids for older chunks.
Generally, it seems preferable to compress chunks oldest to newest. When using the experimental compress_chunk_time_interval option, it is even more so preferable because it allows for the most efficient roll ups. If not, the chunks compressed out of order can "cut off" a rolled up chunk before it was completely full.