From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
To: Amit Kapila <amit.kapila16@gmail.com>
To: Ashwin Agrawal <aagrawal@pivotal.io>
Cc: PostgreSQL mailing lists <pgsql-hackers@postgresql.org>
Subject: Re: Zedstore - compressed in-core columnar storage
Date: Wed, 10 Apr 2019 10:48:22 +0300
Message-ID: <b4c776ce-ca3e-c30c-83d0-5820e19862de@iki.fi> (raw)
In-Reply-To: <b522e7a7-e7f4-47f1-7430-c594f3f712b6@postgrespro.ru>
References: <CALfoeiuF-m5jg51mJUPm5GN8u396o5sA2AF5N97vTRAEDYac7w@mail.gmail.com>
<CAA4eK1Kw1h6SE9dO243T8cvak4CPQcvEXpJMPBzkGdVwRP_tBg@mail.gmail.com>
<7ab5be5f-6404-b52b-e6bf-c1c891ceabb1@iki.fi>
<b522e7a7-e7f4-47f1-7430-c594f3f712b6@postgrespro.ru>
On 10/04/2019 10:38, Konstantin Knizhnik wrote:
> I also a little bit confused about UNDO records and MVCC support in
> Zedstore. Actually columnar store is mostly needed for analytic for
> read-only or append-only data. One of the disadvantages of Postgres is
> quite larger per-record space overhead caused by MVCC.
> It may be critical if you want to store huge timeseries with relatively
> small number of columns (like measurements of some sensor).
> It will be nice to have storage format which reduce this overhead when
> it is not needed (data is not updated).
Sure. Definitely something we need to optimize.
> Right now, even without UNFO pages, size of zedstore is larger than size
> of original Postgres table.
> It seems to be very strange.
If you have a table with a lot of columns, but each column is small,
e.g. lots of boolean columns, the item headers that zedstore currently
stores for each datum take up a lot of space. We'll need to squeeze
those harder to make this competitive. Instead of storing a header for
each datum, if a group of consecutive tuples have the same visibility
information, we could store the header just once, with an array of the
datums, for example.
- Heikki
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To: pgsql-hackers@postgresql.org
Cc: hlinnaka@iki.fi, k.knizhnik@postgrespro.ru, amit.kapila16@gmail.com, aagrawal@pivotal.io
Subject: Re: Zedstore - compressed in-core columnar storage
In-Reply-To: <b4c776ce-ca3e-c30c-83d0-5820e19862de@iki.fi>
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