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jsonb on-disk size calculation - Mailing list pgsql-general

From jian he
Subject jsonb on-disk size calculation
Date
Msg-id CACJufxFRxk7bi_Ez3OTL4PKF_ODrX5xfY_VR8SX=uqMQTVA9wg@mail.gmail.com
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Responses Re: jsonb on-disk size calculation  (Adrian Klaver <adrian.klaver@aklaver.com>)
Re: jsonb on-disk size calculation  (Junwang Zhao <zhjwpku@gmail.com>)
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hi.

drop table x;
create table x(js jsonb);
insert into x select '{"Hello world":1}'::jsonb;
select pg_column_size(js) from x; -- return 33.

based on src/include/utils/jsonb.h
The key and value part is 20 bytes (is it correct?), Jsonb->vl_len_  is 4 byte, JsonbContainer->header is 4 bytes. That's 28 bytes.

but now on-disk is 33 bytes. 
so I am not sure where the remaining bytes are.





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