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MDEV-26029: Sparse files are inefficient on thinly provisioned storage

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The MariaDB implementation of page_compressed tables for InnoDB used
sparse files. In the worst case, in the data file, every data page
will consist of some data followed by a hole. This may be extremely
inefficient in some file systems.

If the underlying storage device is thinly provisioned (can compress
data on the fly), it would be good to write regular files (with sequences
of NUL bytes at the end of each page_compressed block) and let the
storage device take care of compressing the data.

For reads, sparse file regions and regions containing NUL bytes will be
indistinguishable.

my_test_if_disable_punch_hole(): A new predicate for detecting thinly
provisioned storage. (Not implemented yet.)

innodb_atomic_writes: Correct the comment.

buf_flush_page(): Support all values of fil_node_t::punch_hole.
On a thinly provisioned storage device, we will always write
NUL-padded innodb_page_size bytes also for page_compressed tables.

buf_flush_freed_pages(): Remove a redundant condition.

fil_space_t::atomic_write_supported: Remove. (This was duplicating
fil_node_t::atomic_write.)

fil_space_t::punch_hole: Remove. (Duplicated fil_node_t::punch_hole.)

fil_node_t: Remove magic_n, and consolidate flags into bitfields.
For punch_hole we introduce a third value that indicates a
thinly provisioned storage device.

fil_node_t::find_metadata(): Detect all attributes of the file.
This commit is contained in:
Marko Mäkelä
2021-06-28 13:42:43 +03:00
parent b11aa0df85
commit 30edd5549d
9 changed files with 126 additions and 181 deletions
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mysql-test/suite/sys_vars/r/sysvars_innodb.result
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@@ -1754,7 +1754,7 @@ SESSION_VALUE NULL
DEFAULT_VALUE ON
VARIABLE_SCOPE GLOBAL
VARIABLE_TYPE BOOLEAN
VARIABLE_COMMENT Enable atomic writes, instead of using the doublewrite buffer, for files on devices that supports atomic writes. This option only works on Linux with either FusionIO cards using the directFS filesystem or with Shannon cards using any file system.
VARIABLE_COMMENT Enable atomic writes, instead of using the doublewrite buffer, for files on devices that supports atomic writes.
NUMERIC_MIN_VALUE NULL
NUMERIC_MAX_VALUE NULL
NUMERIC_BLOCK_SIZE NULL