MySQL 9.0.0
Source Code Documentation
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The handler interface uses two different formats.
Assume the following table:
This format is used in the input of the write_row()
method. The same format is used by the storage engine in the output buffers of rnd_next()
and index_read()
. Consider the following INSERT statement:
the row buffer that is passed to write_row()
is 352 bytes:
hex | raw | description |
---|---|---|
f0 | . | NULLs bitmask 11110000 denoting that out of 4 columns that could possibly be NULL (c1, c3, c5 and c7) none is actually NULL. |
7b | { | c1=123 stored in 4 bytes (little endian) (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
00 | . | from above (4/4) |
7b | { | c2=123 stored in 4 bytes (little endian) (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
00 | . | from above (4/4) |
04 | . | the length of the following data (for VARCHAR cells): 4 |
61 | a | c3='abcd' - the actual data (1/4) |
62 | b | from above (2/4) |
63 | c | from above (3/4) |
64 | d | from above (4/4) |
a5 | . | 4 wasted bytes for c3 (1/4) |
a5 | . | from above (2/4) |
a5 | . | from above (3/4) |
a5 | . | from above (4/4) |
04 | . | the length of the following data (for VARCHAR cells): 4 |
61 | a | c4='abcd' - the actual data (1/4) |
62 | b | from above (2/4) |
63 | c | from above (3/4) |
64 | d | from above (4/4) |
a5 | . | 4 wasted bytes for c4 (1/4) |
a5 | . | from above (2/4) |
a5 | . | from above (3/4) |
a5 | . | from above (4/4) |
61 | a | c5='abcd ' (padded to 8 bytes with spaces at the end) (1/8) |
62 | b | from above (2/8) |
63 | c | from above (3/8) |
64 | d | from above (4/8) |
20 | from above (5/8) | |
20 | from above (6/8) | |
20 | from above (7/8) | |
20 | from above (8/8) | |
61 | a | c6='abcd ' (padded to 8 bytes with spaces at the end) (1/8) |
62 | b | from above (2/8) |
63 | c | from above (3/8) |
64 | d | from above (4/8) |
20 | from above (5/8) | |
20 | from above (6/8) | |
20 | from above (7/8) | |
20 | from above (8/8) | |
04 | . | the length (occupying 2 bytes) of the following data (for VARCHAR cells): 4 (1/2) |
00 | . | from above (2/2) |
61 | a | c7='abcd' - the actual data (1/4) |
62 | b | from above (2/4) |
63 | c | from above (3/4) |
64 | d | from above (4/4) |
a5 | . | a5 repeats 296 times, wasted bytes for c7 (1/296) |
a5 | . | from above (2/296) |
.. | .. | .. |
a5 | . | from above (296/296) |
Consider the following SELECT statement:
the indexed cells buffer that is passed to index_read()
is 350 bytes:
hex | raw | description |
---|---|---|
00 | . | c1 NULL byte, denoting that c1 is not NULL (would have been 01 is c1 was NULL) |
7b | { | c1=123 stored in 4 bytes (little endian) (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
00 | . | from above (4/4) |
7b | { | c2=123 stored in 4 bytes (little endian) (because c2 cannot be NULL there is no leading byte to indicate NULL or not NULL) (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
00 | . | from above (4/4) |
00 | . | c3 NULL byte, denoting that c3 is not NULL (would have been 01 if c3 was NULL) |
04 | . | c3 length (4), always 2 bytes (1/2) |
00 | . | from above (2/2) |
61 | a | c3='abcd' - the actual data (1/4) |
62 | b | from above (2/4) |
63 | c | from above (3/4) |
64 | d | from above (4/4) |
00 | . | 4 wasted bytes for c3 (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
00 | . | from above (4/4) |
04 | . | c4 length (4), always 2 bytes (no NULL byte for c4) (1/2) |
00 | . | from above (2/2) |
61 | a | c4='abcd' - the actual data (1/4) |
62 | b | from above (2/4) |
63 | c | from above (3/4) |
64 | d | from above (4/4) |
00 | . | 4 wasted bytes for c4 (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
00 | . | from above (4/4) |
00 | . | c5 NULL byte, denoting that c5 is not NULL (would have been 01 if c5 was NULL) |
61 | a | c5='abcd ' (1/8) |
62 | b | from above (2/8) |
63 | c | from above (3/8) |
64 | d | from above (4/8) |
20 | from above (5/8) | |
20 | from above (6/8) | |
20 | from above (7/8) | |
20 | from above (8/8) | |
61 | a | c6='abcd ' (c6 cannot be NULL) (1/8) |
62 | b | from above (2/8) |
63 | c | from above (3/8) |
64 | d | from above (4/8) |
20 | from above (5/8) | |
20 | from above (6/8) | |
20 | from above (7/8) | |
20 | from above (8/8) | |
00 | . | c7 NULL byte |
04 | . | c7 length (4), always 2 bytes (1/2) |
00 | . | from above (2/2) |
61 | a | c7='abcd' - the actual data (1/4) |
62 | b | from above (2/4) |
63 | c | from above (3/4) |
64 | d | from above (4/4) |
00 | . | 296 wasted bytes for c7 (1/296) |
00 | . | from above (2/296) |
.. | .. | .. |
00 | . | from above (296/296) |
We introduce a new format, lets call it TempTable format, that fulfills the following:
For this we introduce a Cell class, which has the following properties:
A Cell object does not store actual user data, only a pointer to it. This way we can create cells that point inside the buffer provided to write_row()
or point inside our own buffer, where the user data is copied for storage.
A row in the TempTable format consists of a set of Cells stored in one buffer, together with the actual user data. The size of a row is the size of all user data + 16 bytes overhead for each cell (for the Cell object).
In the above example both the row (write_row()
format) and the indexed cells (index_read()
format) would be represented like in the table below, in 148 bytes. Think of a POD
hex | raw | description |
---|---|---|
00 | . | c1 NULL byte (00 means not NULL) |
00 | . | 3 bytes padding (1/3) |
00 | . | from above (2/3) |
00 | . | from above (3/3) |
00 | . | c1 length in 4 bytes in whatever is the machine's native byte order (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
04 | . | from above (4/4) |
f1 | . | address in memory where c1 user data is stored (1/8) |
f1 | . | from above (2/8) |
f1 | . | from above (3/8) |
f1 | . | from above (4/8) |
f1 | . | from above (5/8) |
f1 | . | from above (6/8) |
f1 | . | from above (7/8) |
f1 | . | from above (8/8) |
00 | . | c2 NULL byte (00 means not NULL) |
00 | . | 3 bytes padding (1/3) |
00 | . | from above (2/3) |
00 | . | from above (3/3) |
00 | . | c2 length in 4 bytes in whatever is the machine's native byte order (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
04 | . | from above (4/4) |
f2 | . | address in memory where c2 user data is stored (1/8) |
f2 | . | from above (2/8) |
f2 | . | from above (3/8) |
f2 | . | from above (4/8) |
f2 | . | from above (5/8) |
f2 | . | from above (6/8) |
f2 | . | from above (7/8) |
f2 | . | from above (8/8) |
00 | . | c3 NULL byte (00 means not NULL) |
00 | . | 3 bytes padding (1/3) |
00 | . | from above (2/3) |
00 | . | from above (3/3) |
00 | . | c3 length in 4 bytes in whatever is the machine's native byte order (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
04 | . | from above (4/4) |
f3 | . | address in memory where c3 user data is stored (1/8) |
f3 | . | from above (2/8) |
f3 | . | from above (3/8) |
f3 | . | from above (4/8) |
f3 | . | from above (5/8) |
f3 | . | from above (6/8) |
f3 | . | from above (7/8) |
f3 | . | from above (8/8) |
00 | . | c4 NULL byte (00 means not NULL) |
00 | . | 3 bytes padding (1/3) |
00 | . | from above (2/3) |
00 | . | from above (3/3) |
00 | . | c4 length in 4 bytes in whatever is the machine's native byte order (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
04 | . | from above (4/4) |
f4 | . | address in memory where c4 user data is stored (1/8) |
f4 | . | from above (2/8) |
f4 | . | from above (3/8) |
f4 | . | from above (4/8) |
f4 | . | from above (5/8) |
f4 | . | from above (6/8) |
f4 | . | from above (7/8) |
f4 | . | from above (8/8) |
00 | . | c5 NULL byte (00 means not NULL) |
00 | . | 3 bytes padding (1/3) |
00 | . | from above (2/3) |
00 | . | from above (3/3) |
00 | . | c5 length in 4 bytes in whatever is the machine's native byte order (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
08 | . | from above (4/4) |
f5 | . | address in memory where c5 user data is stored (1/8) |
f5 | . | from above (2/8) |
f5 | . | from above (3/8) |
f5 | . | from above (4/8) |
f5 | . | from above (5/8) |
f5 | . | from above (6/8) |
f5 | . | from above (7/8) |
f5 | . | from above (8/8) |
00 | . | c6 NULL byte (00 means not NULL) |
00 | . | 3 bytes padding (1/3) |
00 | . | from above (2/3) |
00 | . | from above (3/3) |
00 | . | c6 length in 4 bytes in whatever is the machine's native byte order (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
08 | . | from above (4/4) |
f6 | . | address in memory where c6 user data is stored (1/8) |
f6 | . | from above (2/8) |
f6 | . | from above (3/8) |
f6 | . | from above (4/8) |
f6 | . | from above (5/8) |
f6 | . | from above (6/8) |
f6 | . | from above (7/8) |
f6 | . | from above (8/8) |
00 | . | c7 NULL byte (00 means not NULL) |
00 | . | 3 bytes padding (1/3) |
00 | . | from above (2/3) |
00 | . | from above (3/3) |
00 | . | c7 length in 4 bytes in whatever is the machine's native byte order (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
04 | . | from above (4/4) |
f7 | . | address in memory where c7 user data is stored (1/8) |
f7 | . | from above (2/8) |
f7 | . | from above (3/8) |
f7 | . | from above (4/8) |
f7 | . | from above (5/8) |
f7 | . | from above (6/8) |
f7 | . | from above (7/8) |
f7 | . | from above (8/8) |
7b | { | c1=123, the address of this is f1f1f1f1 (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
00 | . | from above (4/4) |
7b | { | c2=123, the address of this is f2f2f2f2 (1/4) |
00 | . | from above (2/4) |
00 | . | from above (3/4) |
00 | . | from above (4/4) |
61 | a | c3='abcd', the address of this is f3f3f3f3 (1/4) |
62 | b | from above (2/4) |
63 | c | from above (3/4) |
64 | d | from above (4/4) |
61 | a | c4='abcd', the address of this is f4f4f4f4 (1/4) |
62 | b | from above (2/4) |
63 | c | from above (3/4) |
64 | d | from above (4/4) |
61 | a | c5='abcd ', the address of this is f5f5f5f5 (1/8) |
62 | b | from above (2/8) |
63 | c | from above (3/8) |
64 | d | from above (4/8) |
20 | from above (5/8) | |
20 | from above (6/8) | |
20 | from above (7/8) | |
20 | from above (8/8) | |
61 | a | c6='abcd ', the address of this is f6f6f6f6 (1/8) |
62 | b | from above (2/8) |
63 | c | from above (3/8) |
64 | d | from above (4/8) |
20 | from above (5/8) | |
20 | from above (6/8) | |
20 | from above (7/8) | |
20 | from above (8/8) | |
61 | a | c7='abcd', the address of this is f7f7f7f7 (1/4) |
62 | b | from above (2/4) |
63 | c | from above (3/4) |
64 | d | from above (4/4) |