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| -rw-r--r-- | wiki/mysql/choose-something-else.md | 28 |
1 files changed, 19 insertions, 9 deletions
diff --git a/wiki/mysql/choose-something-else.md b/wiki/mysql/choose-something-else.md index fb9b259..2851327 100644 --- a/wiki/mysql/choose-something-else.md +++ b/wiki/mysql/choose-something-else.md @@ -65,12 +65,15 @@ familiar with other SQL implementations). states](http://dev.mysql.com/doc/refman/5.5/en/server-sql-mode.html), making it harder to carry expectations from manual testing over to code or from tool to tool. -* MySQL uses non-standard and rather unique interpretations of several common - character encodings, including UTF-8 and Latin-1. Implementation details of - these encodings within MySQL, such as the `utf8` encoding's MySQL-specific - 3-byte limit, tend to leak out into client applications. Data that does not - fit MySQL's understanding of the storage encoding will be transformed until - it does, by truncation or replacement, by default. +* MySQL recommends UTF-8 as a character-set, but still defaults to Latin-1. + The implimentation of `utf8` up until MySQL 5.5 was only the 3-byte + [BMP](http://en.wikipedia.org/wiki/Basic_Multilingual_Plane#Basic_Multilingual_Plane). + MySQL 5.5 and beyond supports a 4-byte `utf8`, but confusingly must be set + with the character-set `utf8mb4`. Implementation details of these encodings + within MySQL, such as the `utf8` 3-byte limit, tend to leak out into client + applications. Data that does not fit MySQL's understanding of the storage + encoding will be transformed until it does, by truncation or replacement, by + default. * Collation support is per-encoding, with one of the stranger default configurations: by default, the collation orders characters according to Swedish alphabetization rules, case-insensitively. @@ -102,9 +105,16 @@ familiar with other SQL implementations). ### Preserving Data ... against unexpected changes: like most disk-backed storage systems, MySQL -is as reliable as the disks and filesystems its data lives on. MySQL makes -very little effort to do its own storage validation and error correction, but -this is a limitation shared with many, _many_ other systems. +is as reliable as the disks and filesystems its data lives on. MySQL provides +no additional functionality in terms of mirroring or hardware failure tolerance +(such as [Oracle ASM](http://en.wikipedia.org/wiki/Automatic_Storage_Management)). +However this is a limitation shared with many, _many_ other systems. + +When using the InnoDB storage engine (default since MySQL 5.5), MySQL maintains page +checksums in order to detect corruption caused by underlying storage. However, +many third-party software applications, as sell as users upgrading +from earlier versions of MySQL may be using MyISAM, which will frequently corrupt +data files on improper shutdown. The implicit conversion rules that bite when storing data also bite when asking MySQL to modify data - my favourite example being a fat-fingered |