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help / color / mirror / Atom feedFrom: Aleksander Alekseev <[email protected]>
To: PostgreSQL Hackers <[email protected]>
Cc: Jacob Champion <[email protected]>
Cc: Simon Riggs <[email protected]>
Cc: Alvaro Herrera <[email protected]>
Cc: Matthias van de Meent <[email protected]>
Subject: Re: [PATCH] Compression dictionaries for JSONB
Date: Tue, 28 Jun 2022 15:37:14 +0300
Message-ID: <CAJ7c6TOkpCBFV_GHUfcf5q-aBw9EpkAfDdbhMorLs3QA=OwW5g@mail.gmail.com> (raw)
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Hi Simon,
Many thanks for your feedback!
I'm going to submit an updated version of the patch in a bit. I just
wanted to reply to some of your questions / comments.
> Dictionaries have no versioning. [...]
> Does the order of entries in the dictionary allow us to express a priority? i.e. to allow Huffman coding. [...]
This is something we discussed in the RFC thread. I got an impression
that the consensus was reached:
1. To simply use 32-bit codes in the compressed documents, instead of
16-bit ones as it was done in ZSON;
2. Not to use any sort of variable-length coding;
3. Not to use dictionary versions. New codes can be added to the
existing dictionaries by executing ALTER TYPE mydict ADD ENTRY. (This
also may answer your comment regarding a limit on SQL statement size.)
4. The compression scheme can be altered in the future if needed.
Every compressed document stores algorithm_version (1 byte).
Does this plan of action sound OK to you? At this point it is not too
difficult to make design changes.
--
Best regards,
Aleksander Alekseev
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Subject: Re: [PATCH] Compression dictionaries for JSONB
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