MySQL Bugs: #109919: Clone plugin does not support arbitrary length O

Bug #109919	Clone plugin does not support arbitrary length O_DIRECT files
Submitted:	3 Feb 2023 13:23	Modified:	22 Oct 8:25
Reporter:	Laurynas Biveinis (OCA)	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Clone Plugin	Severity:	S4 (Feature request)
Version:	8.0.32	OS:	Linux
Assigned to:		CPU Architecture:	Any
Tags:	Clone, Contribution

Description:
The clone plugin assumes that any files read or written with O_DIRECT have sizes that are multiples of O_DIRECT block size. This is true for InnoDB, but, in general, O_DIRECT-accessed files can be of any size, because:
- they can be written with the last block padded and then ftruncated to arbitrary size;
- they can be read directly and the last read call will return the actual length of the last file block.

Some other storage engines do use O_DIRECT with arbitrarily-sized files.

How to repeat:
1) Implement clone support for another O_DIRECT-using storage engine with arbitrarily-sized files
2) Clone and observe:

mysqltest: At line 143: Query 'CLONE INSTANCE FROM $USER@$HOST:$PORT IDENTIFIED BY '' $remote_dir_clause' failed.
ERROR 3862 (HY000): Clone Donor Error: 1024 : Error reading file '000043.sst' (errno: 22 - Invalid argument).

Suggested fix:
A possible but not necessary the best fix is

Add a flag to Ha_clone_file to support arbitrary file lengths under O_DIRECT:
o_direct_uneven_file_size. Pass it to clone_client.h/cc
Client::get_aligned_buffer to allocate the buffer that bumps the length to the
next CLONE_OS_ALIGN multiple if it's not already one. Introduce a
pad_for_o_direct helper that performs this calculation for the passed length as
needed.

For writes, if O_DIRECT is enabled and the buffer length is not a multiple of
CLONE_OS_ALIGN, pad it with zeros to the next multiple. Then check the actual
bytes written, and if any padding bytes were actually written, call my_chsize to
truncate the file to the needed size.

Bug 109919 fix option (*) I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

Contribution: bug109919-poc.patch (application/octet-stream, text), 9.14 KiB.

Hello Laurynas,

Thank you for the feature request and contribution!

regards,
Umesh

My contributed patch applies cleanly on 9.0.0 and passes the tests.

The contributed patch applies on 9.1.0 cleanly and passes the tests.