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Diffstat (limited to 'storage/myisam/NEWS')
| -rw-r--r-- | storage/myisam/NEWS | 66 |
1 files changed, 66 insertions, 0 deletions
diff --git a/storage/myisam/NEWS b/storage/myisam/NEWS new file mode 100644 index 00000000..942926a0 --- /dev/null +++ b/storage/myisam/NEWS @@ -0,0 +1,66 @@ +New features compared to NISAM: + +- All file positions have type my_off_t; This enables one to use big + files (2^63 byte) by defining my_off_t to be longlong on OS that supports + big files. +- When creating a table, one can now specify the maximum data file length. + This will be used to calculate the length of row pointers. +- All key segments have their own language definition. +- Some changes to support more types: + The biggest change is that the interface allows MY_ISAM will support + variable length integer types. (Only the interface is implemented) +- All data is stored with low byte first; This makes the data machine + independent. +- All number keys are stored with high byte first to give better packing. +- Support for a true VARCHAR type; A VARCHAR column starts with a length + stored on 2 bytes. +- Tables with VARCHAR may have fixed or dynamic record length. +- There are now 2 different ways to pack keys: + - If the first key part is a space stripped CHAR, a VARCHAR or a BLOB the + 'packed' method is used. This only prefix-compresses the first + key part. + - In other cases prefix packing is used (This also includes the record + pointer into the prefix packing). A key may in the best case be + packed on 2 bytes. +- VARCHAR and CHAR may be up to 65K +- Index on BLOB and VARCHAR. +- One can now have NULL in an index. This takes 0-1 bytes / key. +- MYISAM will allow one to specify one AUTO_INCREMENT column; MYISAM will + automatically update this on INSERT/UPDATE. The AUTO_INCREMENT value can be + reset with myisamchk. +- Max key length will be 500 by default; In cases of longer keys than 250, + a bigger key block size than the default of 1024 byes is used for this key. +- Max number of keys enlarged to 32 as default. This can be enlarged to 64 + without having to recompile myisamchk. +- There is a flag in the MYISAM header that tells if the index file (.MYI) + was closed correctly. +- myisamchk will now mark tables as checked. 'myisamchk --fast' will only + check those tables that doesn't have this mark. +- 'myisamchk -a' stores statistic for key parts (and not only for whole keys + as in NISAM). +- Dynamic size rows will now be much less fragmented when mixing deletes with + update and insert. This is done by automatically combining adjacent deleted + blocks and by extending blocks if the next block is deleted. +- For dynamic size rows, the delete link contains a pointer to itself + (to make repairs easier). +- myisampack (called pack_isam in NISAM) can pack BLOB and VARCHAR + columns. +- One can now disable any key from update; In NISAM one could only disable + the last x keys. +- One can have a UNIQUE constraint on anything (including BLOBS). + This is implemented by a key that contains a hashed number of the whole + record and before inserting a new record, MyISAM will check all records + with the same hash for dupplicates. +- When creating the table, one can define that MyISAM should maintain + a CRC for the whole table (to make isamchk even better). In the case of + dynamic size rows, one will in this case get 1 byte checksum for each row. + (This is a great help for debugging, but it can also be used to keep + MyISAM table 'extra' safe. +- Temporary tables will not write not flushed keys to file on close and + not wait on 'disk full' conditions. + +Interface changes compared to NISAM: + +- mi_create() + - keyinfo->seg must be allocated explicitly. + - One must put number of key segments in keyinfo |