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 Wed, 15 Jul 2020 20:13:05 +0300 (MSK)
Date: Wed, 15 Jul 2020 17:13:04 +0000
From: Nikita Pettik <korablev@tarantool.org>
Message-ID: <20200715171304.GJ26087@tarantool.org>
References: <1594821336-14468-1-git-send-email-alyapunov@tarantool.org>
 <1594821336-14468-10-git-send-email-alyapunov@tarantool.org>
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In-Reply-To: <1594821336-14468-10-git-send-email-alyapunov@tarantool.org>
Subject: Re: [Tarantool-patches] [PATCH v3 09/13] tmx: introduce prepare
 sequence number
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To: Aleksandr Lyapunov <alyapunov@tarantool.org>
Cc: tarantool-patches@dev.tarantool.org

On 15 Jul 16:55, Aleksandr Lyapunov wrote:
> Prepare sequence number is a monotonically increasing ID that is
> assigned to any prepared transaction. This ID is suitable for
> serialization order resolution: the bigger is ID - the latter the
> transaction exist in the serialization order of transactions.

Nit: exists
 
> Note that id of transactions has quite different order in case
> when transaction could yield - an younger (bigger id) transaction
> can prepare/commit first (lower psn) while older tx sleeps in vain.
> 
> Also it should be mentioned that LSN has the same order as PSN,
> but it has two general differences:
> 1. The LSN sequence has no holes, i.e. it is a natural number
> sequence. This property is useless for transaction engine.
> 2. The LSN sequence is provided by WAL writer and thus LSN is not
> available for TX thas was prepared and haven't been committed yet.

Nit: thas -> that

> That feature makes psn more suitable sequence for transactions as
> it allows to order prepared but not committed transaction and
> allows, for example, to create a read view between prepared
> transactions.
> 
> Part of #4897
> ---

LGTM