On 5/26/21 5:29 PM, Bruce Momjian wrote:
> On Tue, May 25, 2021 at 01:55:13PM +0300, Aleksander Alekseev wrote:
>> Hi hackers,
>>
>> Back in 2016 while being at PostgresPro I developed the ZSON extension [1]. The
>> extension introduces the new ZSON type, which is 100% compatible with JSONB but
>> uses a shared dictionary of strings most frequently used in given JSONB
>> documents for compression. These strings are replaced with integer IDs.
>> Afterward, PGLZ (and now LZ4) applies if the document is large enough by common
>> PostgreSQL logic. Under certain conditions (many large documents), this saves
>> disk space, memory and increases the overall performance. More details can be
>> found in README on GitHub.
> I think this is interesting because it is one of the few cases that
> allow compression outside of a single column. Here is a list of
> compression options:
>
> https://momjian.us/main/blogs/pgblog/2020.html#April_27_2020
>
> 1. single field
> 2. across rows in a single page
> 3. across rows in a single column
> 4. across all columns and rows in a table
> 5. across tables in a database
> 6. across databases
>
> While standard Postgres does #1, ZSON allows 2-5, assuming the data is
> in the ZSON data type. I think this cross-field compression has great
> potential for cases where the data is not relational, or hasn't had time
> to be structured relationally. It also opens questions of how to do
> this cleanly in a relational system.
>
I think we're going to get the best bang for the buck on doing 2, 3, and
4. If it's confined to a single table then we can put a dictionary in
something like a fork. Maybe given partitioning we want to be able to do
multi-table dictionaries, but that's less certain.
cheers
andrew
--
Andrew Dunstan
EDB: https://www.enterprisedb.com