The change to move to a char(36) is an incremental good that brought a breaking change for some folks, but it is easily rectified. InnoDB stores data in the PRIMARY KEY order and all the secondary keys also contain PRIMARY KEY. My previous recommendation to allow the underlying db type to remain unchanged (through configuration) seems appropriate, as a varchar(36) is completely compatible with UUID fields and had been used up until this change. UUID has 36 characters which make it bulky. You don't have to manually assign its value before save - value will be automatically generated.Ĭertainly you want to hand check everything, but migration script generation serves a very important purpose in some situations and create a nice baseline for hand written scripts.when they are mostly accurate. you really need them because of generating unique ids from different places (and have not figured out another way to do it). creates a primary column which value will be automatically generated with uuid. Generalization: The inefficiency applies to any 'random' access - UUID / MD5 / RAND () / etc. It is designed in such a way that it generates a number which is unique globally according to space and time. It can require less storage space than fixed-length types, because it uses only as much space as it needs (i.e., less space is used to store shorter values). That means compressing the 32 characters (36 or more with separators) to the 16-bit format or back to the human-readable format. It does if your primary key uses the primary column uuid generation strategy. A UUID is a Universal Unique Identifier specified by RFC 4122 (It is a Universally Unique Identifier URN Namespace) and 128-bit long value. Why Every 4 bits of the UUID represented is hex therefore that hex character is 8 bits of storage. Solutions Of course there are some best practices that MySQL users can follow to avoid those problems: use a smaller datatype to store their UUIDs: BINARY (16) store the UUIDs sequentially: use UUIDTOBIN (. according to High Performance MySQL book: VARCHAR stores variable-length character strings and is the most common string data type. These function will be used to convert from the human-readable format (char/varchar) to the compact format (binary) and back.
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