We used to define a native unary function crc32() that computes the CRC-32
of a string using the ISO 3309 polynomial that is being used by zlib
and many others.
Often, CRC is computed in pieces. To faciliate this, we introduce a
2-ary variant of the function that inputs a previous CRC as the first
argument: CRC32('MariaDB')=CRC32(CRC32('Maria'),'DB').
InnoDB and MyRocks use a different polynomial, which was implemented
in SSE4.2 instructions that were introduced in the
Intel Nehalem microarchitecture. This is commonly called CRC-32C
(Castagnoli).
We introduce a native function that uses the Castagnoli polynomial:
CRC32C('MariaDB')=CRC32C(CRC32C('Maria'),'DB'). This allows
SELECT...INTO DUMPFILE to be used for the creation of files with
valid checksums, such as a logically empty InnoDB redo log file
ib_logfile0 corresponding to a particular log sequence number.
ebc6494...
by
Rucha Deodhar <email address hidden>
MDEV-26238: Remove inconsistent behaviour of --default-* options
in my_print_defaults
Analysis: --defaults* option is recognized anywhere in the commandline
instead of only at the beginning because handle_options() recognizes
options in any order.
Fix: use get_defaults_options() which recognizes --defaults* options only at
the beginning. After this is done, we only want to recognize other options
given in any order which can be done using handle_options(). So only skip
--defaults* options and pass rest of them to handle_options().
Also, removed -e, -g and -c because only my_print_defaults supports them.
MDEV-27266 Improve UCA collation performance for utf8mb3 and utf8mb4
Adding two levels of optimization:
1. For every bytes pair [00..FF][00..FF] which:
a. consists of two ASCII characters or makes a well-formed two-byte character
b. whose total weight string fits into 4 weights
(concatenated weight string in case of two ASCII characters,
or a single weight string in case of a two-byte character)
c. whose weight is context independent (i.e. does not depend on contractions
or previous context pairs)
store weights in a separate array of MY_UCA_2BYTES_ITEM,
so during scanner_next() we can scan two bytes at a time.
Byte pairs that do not match the conditions a-c are marked in this array
as not applicable for optimization and scanned as before.
2. For every byte pair which is applicable for optimization in #1,
and which produces only one or two weights, store
weights in one more array of MY_UCA_WEIGHT2. So in the beginning
of strnncoll*() we can skip equal prefixes using an even more efficient
loop. This loop consumes two bytes at a time. The loop scans while the
two bytes on both sides produce weight strings of equal length
(i.e. one weight on both sides, or two weight on both sides).
This allows to compare efficiently:
- Context independent sequences consisting of two ASCII characters
- Context independent 2-byte characters
- Contractions consisting of two ASCII characters, e.g. Czech "ch".
- Some tricky cases: "ss" vs "SHARP S"
("ss" produces two weights, 0xC39F also produces two weights)
