The idea is using them as primary keys rather than the default integers. Thus the leftmost group varies the fastest (10 times per microsecond). UUID (Universally Unique Identifiers) also known as GUID (Globally Unique Identifier). ![]() ![]() Here are just a few examples: Storing UUID and Generated Columns Storing UUID Values in MySQL Illustrating Primary Key models in InnoDB and their impact on disk usage MySQL UUID Smackdown: UUID vs. MySQL’s UUID() uses version 1, which implies, as explained in paragraph 4.1.2 of the RFC, that the three leftmost dash-separated groups are a 8-byte timestamp: leftmost group is the low four bytes of the timestamp second group is the middle two bytes, third group is the high (most significant) two bytes of the timestamp. NovemYves Trudeau If you do a quick web search about UUIDs and MySQL, you’ll get a fair number of results. They exist in several versions, and different sources can generate different versions. To understand that, we need to learn more about UUIDs. The fourth number preserves temporal uniqueness in case the timestamp value loses monotonicity (for example, due to daylight saving time). It is a unique identifier that is used to identify objects, without relying on any external reference. MySQL uses UUID version 1 which is a 128-bit number represented by a utf8 string of five hexadecimal numbers The first three numbers are generated from a timestamp. UUID values are unique across tables, databases, and even servers that allow you to merge rows from different databases or distribute databases across servers. It is a 128-bit long value that is unique across the globe and is generated using an algorithm. However, if we have a choice, as the binary form is shorter, it looks more logical to index it, not the text form – the index will be smaller and thus faster to traverse, faster to backup…įinally, there is the question of how to smartly re-arrange bytes in the binary form. UUID stands for Universally Unique Identifier and is specified by the Request for Comments 4122 or RFC 4122. MySQL 5.6.46, 5.7.28, nor 8.0.18 do not appear to have this issue. That is a new feature introduced in MySQL 5.7.8. Even though id_text is a virtual column, it is possible, as above, to add an index on it (in that case, the index does occupy disk space).
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