You can put the uuid in another field (secretkey, for example). When you have a lot of records, the auto increment int is better for performance. Besides the quadruple disk space used, which may be largely negligible after additional data is added, they appear to me to be the same. Of course, there are other ways) If you use integer, someone can loop through all profile pictures that you have. I often come across columns that are varchar (255), so presumably this is a convention of sorts. What I am essentially trying to discover is difference in efficiency between the two approaches. 11 This question already has answers here : MySQL - varchar length and performance (2 answers) Closed 4 years ago. you really need them because of generating unique ids from different places (and have not figured out another way to do it). The use case for this type of set up would be the traditional primary key for inter-table relationships, with unique identifier used for inter-system relationships. Generalization: The inefficiency applies to any 'random' access - UUID / MD5 / RAND () / etc. This means that the storage requirements are different - a CHAR always takes the same amount of space regardless of what you store, whereas the storage requirements for a VARCHAR vary depending on the specific string stored. Whereas many people stress over the advantages of either, what are the disadvantages cancelled out by using both data types? A CHAR field is a fixed length, and VARCHAR is a variable length field. I was initially sceptical towards using UUIDs as primary keys, and indeed I still am, however I see potential here to create a flexible database that can use both. In MySQL, you can store UUID values in a compact format ( BINARY) and display them in human-readable format ( VARCHAR) with help of the following functions: UUIDTOBIN BINTOUUID ISUUID Notice that UUIDTOBIN (), BINTOUUID (), and ISUUID () functions are only available in MySQL 8.0 or later. But here comes the problem, using it as PRIMARY KEY causes the problems described below. The test and results are shown below, but if you just want the summary, it indicates that INT AUTOINCREMENT and BINARY(16) RANDOM have identical performance on data ranges up to 200,000 (the database was pre-populated prior to tests). Many people store UUID as char (36) and use as row identity value (PRIMARY KEY) because it is unique across every table, every database and every server and allow easy merging of records from different databases. ![]() ![]() Now, we create our domain class using Hibernate annotations to map it to our existing MySQL table. The rest of the table structure can be similar to the image. It was when I reached the final one BINARY(16) that I started to compare performance with basic auto-increment integer. Since we know the format of the UUID when represented as a String, we know that it has a length of 36 characters, so we can define the column as VARCHAR (36). The formats I used changed as I became less naive from: These functions allow us to store UUID values in a compact format (BINARY) and display them in a human-readable format (VARCHAR). I've been using UUIDs in my systems for a while now for a variety of reasons ranging from logging to delayed correlation.
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