Re: Historic snapshot doesn't track txns committed in BUILDING_SNAPSHOT state

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From: =?ISO-8859-1?B?Y2NhNTUwNw==?= <[email protected]>
To: =?ISO-8859-1?B?QmVydHJhbmQgRHJvdXZvdA==?= <[email protected]>
Cc: =?ISO-8859-1?B?TWljaGFlbCBQYXF1aWVy?= <[email protected]>
Cc: =?ISO-8859-1?B?cGdzcWwtaGFja2Vycw==?= <[email protected]>
Subject: Re: Historic snapshot doesn't track txns committed in BUILDING_SNAPSHOT state
Date: Tue, 13 Aug 2024 15:32:42 +0800
Message-ID: <[email protected]> (raw)

Hi,

- I re-read your comments in [0] and it looks like you've concern about
- the 2 "if" I'm proposing above and the fast forward handling. Is that the case
- or is your fast forward concern unrelated to my proposals?

In your proposals, we will just return when fast forward. But I think we need
handle&nbsp;XLOG_HEAP2_NEW_CID or&nbsp;XLOG_HEAP_INPLACE even if we are fast
forwarding as it decides whether the snapshot will track the transaction or not.

During fast forward, if there is a transaction that generates XLOG_HEAP2_NEW_CID
but no XLOG_XACT_INVALIDATIONS(I'm not sure), the snapshot won't track this
transaction in your proposals, I think it's wrong from a build snapshot perspective.

Although we don't decode anything during fast forward, the snapshot might be
serialized to disk when CONSISTENT, it would be better to keep the snapshot correct.

- Not sure what happened but it looks like your reply in [0] is not part of the
- initial thread [1], but created a new thread instead, making the whole
- conversation difficult to follow.

I'm not sure what happened but I attach the new thread to the CF:

https://commitfest.postgresql.org/49/5029

--
Regards,
ChangAo Chen

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