Re: Undo logs

From: Dilip Kumar <dilip(dot)kumar(at)enterprisedb(dot)com>
To: Dilip Kumar <dilipbalaut(at)gmail(dot)com>
Cc: Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Undo logs
Date: 2018-08-31 10:24:06
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On Fri, Aug 31, 2018 at 3:08 PM, Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> Hello hackers,
> As Thomas has already mentioned upthread that we are working on an
> undo-log based storage and he has posted the patch sets for the lowest
> layer called undo-log-storage.
> This is the next layer which sits on top of the undo log storage,
> which will provide an interface for prepare, insert, or fetch the undo
> records. This layer will use undo-log-storage to reserve the space for
> the undo records and buffer management routine to write and read the
> undo records.
> To prepare an undo record, first, it will allocate required space
> using undo_log_storage module. Next, it will pin and lock the required
> buffers and return an undo record pointer where it will insert the
> record. Finally, it calls the Insert routine for final insertion of
> prepared record. Additionally, there is a mechanism for multi-insert,
> wherein multiple records are prepared and inserted at a time.
> To fetch an undo record, a caller must provide a valid undo record
> pointer. Optionally, the caller can provide a callback function with
> the information of the block and offset, which will help in faster
> retrieval of undo record, otherwise, it has to traverse the undo-chain.
> These patch sets will apply on top of the undo-log-storage branch [1],
> commit id fa3803a048955c4961581e8757fe7263a98fe6e6.
> [1]
> undo_interface_v1.patch is the main patch for providing the undo interface.
> undo_interface_test_v1.patch is a simple test module to test the undo
> interface layer.

Thanks to Robert Haas for designing an early prototype for forming
undo record. Later, I’ve completed the remaining parts of the code
including undo record prepare, insert, fetch and other related APIs
with help of Rafia Sabih. Thanks to Amit Kapila for providing valuable
design inputs.

Dilip Kumar

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