I am trying to increase performance in MySQL. once of the thing that I learned in using Latin1 charset is faster than using UTF8 because latin1 uses less bytes.. But I am wondering what will happen to the data if I changed the collation? in my application today most of the things are in Amerian english but I can't guarantee that there won't be any other languages stores as well. it someone store data other than english I don't really care about that data much.
My question:
1) if I changed the collation in my databases to latin1 what will happen to the data if it was not written in American English?
2) which lation1_? do I use latin1_bin, latin1_general_ci, or latin1_general_cs? and if possible what is the difference?
3) when changing the collation of the database do I need to also change the collation of each table separately?
Thanks
UTF 8 only uses extra bytes if it has strange characters. So really, you should NOT change your collation. it won't help. UTF 16 was developed to hold all characters of all languages, and yes, it uses 16 bits so if you were using utf16 I would suggest utf8 if you mostly had standard latin characters. utf 8 is the compromise. it has a special character that means "more bytes coming", and if it sees it, it groups the next ones together. But if all you have is latin characters, the bytes will be exactly the same number as with latin collation.
to answer specifically, you can set the default colation for new tables, but yes, you have to do it for each one of the existing ones. you could do it with an sql statement that lists the tables then runs the sql statement on each, to change it. (change 1 and notice the sql statement). but again, don't do it. utf8 is the standard for a reason. your performance issues are elsewhere.
Related
In my codeigniter project I am using MySQL as database. It's collation is 'latin1_swedish_ci'. Now I need to scale my website to store 'Polish', 'German', 'French', 'Ukrainian', 'Dutch' in addition to 'English'. But I don't know which collation to be used. I found different answers for different language in web. But I need a general one. Please help me to find out a solution.
(Alvaro's answer is good; I am adding some notes.)
If you are using MySQL 5.5 or 5.6 and have VARCHAR(255), see this for some issues you might run into.
ALTER TABLE t CONVERT TO CHARACTER SET utf8mb4;
(for each table) is probably the simplest way to convert to UTF-8. Caution: test it separately from production, and test that the Western European text does not get mangled. If you get gibberish or question marks, see this
In converting to CHARACTER SET utf8mb4, the preferred COLLATION is utf8mb4_unicode_520_ci. (With MySQL 8.0, there is a better one.)
utf8mb4 will let you handle all the languages of the world, so this should be the last 'conversion' necessary.
Before caring about collation, you need to migrate to a Unicode compatible encoding first. As the name suggest, Latin-1* is designed for Latin script and cannot encode all Polish characters and, of course, none of the Cyrillic script. The obvious choice in 2019 is UTF-8, which corresponds to utf8mb4 in MySQL terminology.
Beware though that this may not be trivial. If your application assumes single byte encodings any text manipulation feature may need to be reviewed and maybe fixed. For instance, the € symbol has a length of 1 byte in Windows-1252 but it's 3 bytes in UTF-8. Let's say you have code that strips it from a string like '29.92€'. If your application removes the last byte, code that was working flawlessly in a single-byte encoding will no longer be valid in a multi-byte encoding because one byte isn't one character any more. Or, even in MySQL itself, some as simple as regular expressions wasn't multibyte safe until MySQL 8.0.4.
Once you address this, you need to pick a proper collation. Since you're mixing languages you need a general purpose Unicode one. Here's a good overview.
(*) MySQL is actually lying to you. When it says Latin-1 it actually means Windows-1252.
For some reason I don't know, I have some Kamailio tables with utf32_general_ci collation (location in example) and others with latin1_swedish_ci.
I try to find answer on github repos (https://github.com/kamailio/kamailio/blob/4.4/scripts/mysql/my_create.sql) but collation is not specified.
That's right? Does matters? Which one it's right choice?
My Kamailio version is 4.4.3.
What is Kamailio? What does it store in a database?
In general, all software today should be using full UTF-8 characterset encoding. In MySQL, the syntax is CHARACTER SET utf8mb4.
You mentioned two COLLATIONs; they have to do with sort order, not character encoding. The two mentioned correspond to character sets
utf32 -- 4 bytes per character quite wasteful of space; virtually no one uses it; there is no good reason (that I can think of) to use it today.
latin1 -- 1 byte per character; handles western Europe, but none of Asia. It is an old default in MySQL (hence your tables having it).
I do not know the ramifications of trying to change Kamailio.
One thing to note in how MySQL deals with character set differences: You must specify the encoding in the client when connecting to MySQL. Then, when INSERTing and SELECTing, MySQL will convert (if necessary, and if possible) between the client encoding and column encoding. Because of this automatic conversion, you will currently see nothing wrong for western European characters. But Greek, Chinese, etc will be mangled/lost when attempting to store into latin1.
What are the advantages/disadvantages between using utf8 as a charset against using latin1?
If utf can support more chars and is used consistently wouldn't it always be the better choice? Is there any reason to choose latin1?
UTF8 Advantages:
Supports most languages, including RTL languages such as Hebrew.
No translation needed when importing/exporting data to UTF8 aware components (JavaScript, Java, etc).
UTF8 Disadvantages:
Non-ASCII characters will take more time to encode and decode, due to their more complex encoding scheme.
Non-ASCII characters will take more space as they may be stored using more than 1 byte (characters not in the first 127 characters of the ASCII characters set). A CHAR(10) or VARCHAR(10) field may need up to 30 bytes to store some UTF8 characters.
Collations other than utf8_bin will be slower as the sort order will not directly map to the character encoding order), and will require translation in some stored procedures (as variables default to utf8_general_ci collation).
If you need to JOIN UTF8 and non-UTF8 fields, MySQL will impose a SEVERE performance hit. What would be sub-second queries could potentially take minutes if the fields joined are different character sets/collations.
Bottom line:
If you don't need to support non-Latin1 languages, want to achieve maximum performance, or already have tables using latin1, choose latin1.
Otherwise, choose UTF8.
latin1 has the advantage that it is a single-byte encoding, therefore it can store more characters in the same amount of storage space because the length of string data types in MySql is dependent on the encoding. The manual states that
To calculate the number of bytes used to store a particular CHAR,
VARCHAR, or TEXT column value, you must take into account the
character set used for that column and whether the value contains
multibyte characters. In particular, when using a utf8 Unicode
character set, you must keep in mind that not all characters use the
same number of bytes. utf8mb3 and utf8mb4 character sets can require
up to three and four bytes per character, respectively. For a
breakdown of the storage used for different categories of utf8mb3 or
utf8mb4 characters, see Section 10.9, “Unicode Support”.
Furthermore lots of string operations (such as taking substrings and collation-dependent compares) are faster with single-byte encodings.
In any case, latin1 is not a serious contender if you care about internationalization at all. It can be an appropriate choice when you will be storing known safe values (such as percent-encoded URLs).
#Ross Smith II, Point 4 is worth gold, meaning inconsistency between columns can be dangerous.
To add value to the already good answers, here is a small performance test about the difference between charsets:
A modern 2013 server, real use table with 20000 rows, no index on concerned column.
SELECT 4 FROM subscribers WHERE 1 ORDER BY time_utc_str; (4 is cache buster)
varchar(20) CHARACTER SET latin1 COLLATION latin1_bin: 15ms
varbinary(20): 17ms
utf8_bin: 20ms
utf8_general_ci: 23ms
For simple strings like numerical dates, my decision would be, when performance is concerned, using utf8_bin (CHARACTER SET utf8 COLLATE utf8_bin). This would prevent any adverse effects with other code that expects database charsets to be utf8 while still being sort of binary.
Fixed-length encodings such as latin-1 are always more efficient in terms of CPU consumption.
If the set of tokens in some fixed-length character set is known to be sufficient for your purpose at hand, and your purpose involves heavy and intensive string processing, with lots of LENGTH() and SUBSTR() stuff, then that could be a good reason for not using encodings such as UTF-8.
Oh, and BTW. Do not confuse, as you seem to do, between a character set and an encoding thereof. A character set is some defined set of writeable glyphs. The same character set can have multiple distinct encodings. The various versions of the unicode standard each constitute a character set. Each of them can be subjected to either UTF-8, UTF-16 and "UTF-32" (not an official name, but it refers to the idea of using full four bytes for any character) encoding, and the latter two can each come in a HOB-first or HOB-last flavour.
I know that MySQL has default of latin1 encoding and apparently it takes 1 byte to store a character in latin1 and 3 bytes to store a character in utf-8 - is that correct?
I am working on a site that I hope will be used globally. Do I absolutely need to have utf-8? Or will I be able to get away with using latin1?
Also, I tried to change some tables from latin1 to utf8 but I got this error:
Speficief key was too long; max key length is 1000 bytes
Does anyone know the solution to this? And should I really solve that or may latin1 be enough?
Thanks,
Alex
it takes 1 byte to store a character in latin1 and 3 bytes to store a character in utf-8 - is that correct?
It takes 1 bytes to store a latin1 character and 1 to 3 bytes to store a UTF8 character.
If you only use basic latin characters and punctuation in your strings (0 to 128 in Unicode), both charsets will occupy the same length.
Also, I tried to change some tables from latin1 to utf8 but I got this error: "Speficief key was too long; max key length is 1000 bytes" Does anyone know the solution to this? And should I really solve that or may latin1 be enough?
If you have a column of VARCHAR(334) or longer, MyISAM wont't let you create an index on it since there is remote possibility of the column to occupy more that 1000 bytes.
Note that keys of such length are rarely useful. You can create a prefixed index which will be almost as selective for any real-world data.
At a bare minimum I would suggest using UTF-8. Your data will be compatible with every other database out there nowadays since 90%+ of them are UTF-8.
If you go with LATIN1/ISO-8859-1 you risk the data being not properly stored because it doesn't support international characters... so you might run into something like the left side of this image:
If you go with UTF-8, you don't need to deal with these headaches.
Regarding your error, it sounds like you need to optimize your database. Consider this: http://bugs.mysql.com/bug.php?id=4541#c284415
It would help if you gave specifics on your table schema and column for that issue.
If you allow users to post in their own languages, and if you want users from all countries to participate, you have to switch at least the tables containing those posts to UTF-8 - Latin1 covers only ASCII and western European characters. The same is true if you intend to use multiple languages for your UI. See this post for how to handle migration.
In my experience, if you plan to support Arabic, Russian, Asian languages or others, the investment in UTF-8 support upfront will pay off down the line. However, depending on your circumstances you may be able to get away with English for a while.
As for the error, you probably have a key or index field with more than 333 characters, the maximum allowed in MySQL with UTF-8 encoding. See this bug report.
We did an application using Latin because it was the default. But later on we had to change everything to UTF because of spanish characters, not incredible difficult but no point having to change things unnecessarily.
So short answer is just go with UTF-8 from the beginning, it will save you trouble later on.
Since the max length of a key is 1000 BYTES, if you use utf8, then this will limmit you to 333 characters.
However MySQL is different form Oracle for charset. In Oracle you can't have a different character set per column, wheras in MySQL you can, so may be you can set the key to latin1 and other columns to utf8.
Finally I believe only defunct version 6.0alpha (ditched when Sun bought MySQL) could accomodate unicode characters beyound the BMP (Basic Multilingual Plan). So basically, even with UTF-8, you won't have all the whole unicode character set. In practice this is only a problem for rare Chinese characters, if that really matters to you.
I am not an expert, but I always understood that UTF-8 is actually a 4-byte wide encoding set, not 3. And as I understand it, the MySQL implementation of utf8_unicode_ci only handles a 3-byte wide encoding set...
If you want the full UTF-8 4-byte character encoding, you need to use utf8mb4_unicode_ci encoding for your MySQL database/tables.
Current best practice is to never use MySQL's utf8 character set. Use utf8mb4 instead, which is a proper implementation of the standard.
See Adam Hooper's Explanation for more detail.
Note that in utf8mb4, characters have a variable number of bytes. As the name implies, characters are up to four bytes. For characters in the the latin character set, encoded as utf8mb4, they still occupy only one byte. Other characters, including those with accents, Kanji, and emoji's require two, three, or four bytes to store.
The Specified key was too long; max key length is 1000 bytes error occurs when an index contains columns in utf8mb4 because the index may be over this limit. You'll need to shorten the column length of some character columns or shorten the length of the index on the columns using this syntax to ensure that it is shorter than the limit.
ALTER TABLE.. ADD INDEX `myIndex` ( column1(15), column2(200) );
Does anyone know why latin1_swedish is the default for MySQL. It would seem to me that UTF-8 would be more compatible right?
Defaults are usually chosen because they are the best universal choice, but in this case it does not seem thats what they did.
As far as I can see, latin1 was the default character set in pre-multibyte times and it looks like that's been continued, probably for reasons of downward compatibility (e.g. for older CREATE statements that didn't specify a collation).
From here:
What 4.0 Did
MySQL 4.0 (and earlier versions) only supported what amounted to a combined notion of the character set and collation with single-byte character encodings, which was specified at the server level. The default was latin1, which corresponds to a character set of latin1 and collation of latin1_swedish_ci in MySQL 4.1.
As to why Swedish, I can only guess that it's because MySQL AB is/was Swedish. I can't see any other reason for choosing this collation, it comes with some specific sorting quirks (ÄÖÜ come after Z I think), but they are nowhere near an international standard.
latin1 is the default character set. MySQL's latin1 is the same as the
Windows cp1252 character set. This means it is the same as the
official ISO 8859-1 or IANA (Internet Assigned Numbers Authority)
latin1, except that IANA latin1 treats the code points between 0x80
and 0x9f as “undefined,” whereas cp1252, and therefore MySQL's latin1,
assign characters for those positions.
from
http://dev.mysql.com/doc/refman/5.0/en/charset-we-sets.html
Might help you understand why.
Using a single-byte encoding has some advantages over multi-byte encondings, e.g. length of a string in bytes is equal to length of that string in characters. So if you use functions like SUBSTRING it is not intuitively clear if you mean characters or bytes. Also, for the same reasons, it requires quite a big change to the internal code to support multi-byte encodings.
Most strange features of this kind are historic. They did it like that long time ago, and now they can't change it without breaking some app depending on that behavior.
Perhaps UTF8 wasn't popular then. Or perhaps MySQL didn't support charsets where multiple bytes encode on character then.
To expand on why not utf8, and explain a gotcha not mentioned elsewhere in this thread be aware there is a gotcha with mysql utf8. It's not utf8! Mysql has been around for a long time, since before utf8 existed. As explained above this is likely why it is not the default (backwards comparability, and expectations of 3rd party software).
In the time when utf8 was new and not commonly used, it seems mysql devs added basic utf8 support, incorrectly using 3 bytes of storage. Now that it exists, they have chosen not to increase it to 4 bytes or remove it. Instead they added utf8mb4 "multi byte 4" which is real 4 byte utf8.
Its important that anyone migrating a mysql database to utf8 or building a new one knows to use utf8mb4. For more information see https://adamhooper.medium.com/in-mysql-never-use-utf8-use-utf8mb4-11761243e434