I'm trying to do an INSERT into a mysql db and it fails when any of the values are longer than 898 characters. Is there somewhere to get or, better, set this maximum value? I'll hack the string into chunks and store 'em in separate rows if I must, but I'd like to be able to insert up to 2k at a time.
I'm guessing this is php issue as using LONGTEXT or BLOB fields should be more than enough space in the db.
Thanks.
Side Note:
When you get into working with large blobs and text columns, you need to watch out for the MySQL max_allowed_packet variable. I believe it defaults to at least 1M.
I'm assuming this is a varchar column you're trying to insert into? If so, I assume the maximum length has been set to 898 or 900 or something like that.
In MySQL 5 the total row size can be up to 65,536 bytes so a varchar can be defined to whatever size keeps the total row size under that.
If you need larger use text (65,536) or longtext (4 billion?).
Related
We have a large table (10M + rows), with two BLOB columns. When checking certain entries with command line, the full contents are present, however using PHP to output the results, it cuts one of the BLOB fields short by about 200 characters or so at random. I already changed the memory limit in PHP.ini to 1024MB. Is there any other cap that I should be checking?
The exact same script pulling the exact same row causes the random string length to be output. It's using a simple mysql_fetch_row() method.
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What are the optimum varchar sizes for MySQL?
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I am designing a database which will to store JSON strings of various sizes. I'm considering using different tables (each with two columns, 'id' and 'data') to store different string sizes (tinytext - bigtext). In this case each table would be searched, starting with the table containing the smallest string sizes.
I'm also considering using a single table with a single string size and using multiple rows to store large JSON strings.
..or I could just create a table with a large VARCHAR size and save myself some development time.
There are two points that I am designing around:
In some cases, mysql stores small pieces of data "in row" which helps performance. What does this mean and how can I take advantage of this?
In some cases, mysql processes VARCHAR as its largest possible size. When does this happen and how can I avoid it?
From the database point of view there is no particular "good" length for varchar. However try to keep maximum row size under 8kb, including non-clustered indexes. Then you will avoid MySQL storing data out of row, which hampers performance.
use 255
Why historically do people use 255 not 256 for database field magnitudes?
Although, as a side note, if you are working with PHP and trying to insert strings in excess of 1000 characters, you will need to truncate to your max col size on the PHP side before inserting, or you will hit an error.
I have a pretty simple question. I am inserting a lot of records at once in a MySQL table. It works for about 2000 records (actually a bit more). But say I want to insert 3000 records, than it doesn't do anything.
I'm working through AS3 sending an array containing all the records via AMFPHP to a simple PHP script to parse and insert the array.
Is this normal, or should I look into it?
Currently I'm slicing my array in parts of 2000 records, and sending a couple AMFPHP requests instead of just 1.
PHP's queries are limited by the "max_allowed_packet" configuration option. It defines the absolute length limit, in characters, that a query string can be. Note that this isn't just the total size of the data being inserted, it's the entire query string. SQL commands, punctuation, spaces, etc...
Check how long your 3000 record version is vs. the 2000 one, and then get your server's packet length limit:
SHOW VARIABLES WHERE Variable_name LIKE '%max_allowed_packet%'
If your 3000-record version is longer than this limit, the query will defnitely fail because it'll be chopped off somewhere part-way
I don't think there is really a limit in the number of inserts in one query.
Instead, there is a limit in the size of the query you can send to MySQL
See :
max_allowed_packet
Packet too large
So, basically, this depends on the amount of data you have in each insert.
I would ensure max_allowed_packet is larger than your PHP SQL query.
http://dev.mysql.com/doc/refman/5.5/en/packet-too-large.html
I think PHP doesn't limit the amount of inserted query at one, instead its limit the amount of the memory usage that can be taken by script, and max time of the execution.
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Possible Duplicate:
Importance of varchar length in MySQL table
When using VARCHAR (assuming this is the correct data type for a short string) does the size matter? If I set it to 20 characters, will that take up less space or be faster than 255 characters?
Yes, is matter when you indexing multiple columns.
Prefixes can be up to 1000 bytes long (767 bytes for InnoDB tables). Note that prefix limits are measured in bytes, whereas the prefix length in CREATE TABLE statements is interpreted as number of characters. Be sure to take this into account when specifying a prefix length for a column that uses a multi-byte character set.
source : http://dev.mysql.com/doc/refman/5.0/en/column-indexes.html
In a latin1 collation, you can only specify up 3 columns of varchar(255).
While can specify up to 50 columns for varchar(20)
In-directly, without proper index, it will slow-down query speed
In terms of storage, it does not make difference,
as varchar stand for variable-length strings
In general, for a VARCHAR field, the amount of data stored in each field determines its footprint on the disk rather than the maximum size (unlike a CHAR field which always has the same footprint).
There is an upper limit on the total data stored within all fields of an index of 900 bytes (900 byte index size limit in character length).
The larger you make the field, the more likely people will try to use for purposes other than what you intended - and the greater the screen real-estate required to show the value - so its good practice to try to pick the right size, rather than assuming that if you make it as large as possible it will save you having to revisit the design.
The actual differences are:
TINYTEXT and other TEXT fields are stored separately from in-memory row inside MySQL heap, whereas VARCHAR() fields add up to 64k limit (so you can have more than 64k in TINYTEXTs, whereas you won't with VARCHAR).
TINYTEXT and other 'blob-like' fields will force SQL layer (MySQL) to use on-disk temporary tables whenever they are used, whereas VARCHAR will be still sorted 'in memory' (though will be converted to CHAR for the full width).
InnoDB internally doesn't really care whether it is tinytext or varchar. It is very easy to verify, create two tables, one with VARCHAR(255), another with TINYINT, and insert a record to both. They both will take single 16k page - whereas if overflow pages are used, TINYTEXT table should show up as taking at least 32k in 'SHOW TABLE STATUS'.
I usually prefer VARCHAR(255) - they don't cause too much of heap fragmentation for single row, and can be treated as single 64k object in memory inside MySQL. On InnoDB size differences are negligible.
In the documentation of MySQL:
http://dev.mysql.com/doc/refman/5.0/en/char.html
You have a table that indicates the bytes of a VARCHAR(4) (vs a CHAR(4)).
A simple VARCHAR(4) without string, only 1 byte. Then, a simple VARCHAR(255) without string is 1byte. A VARCHAR(4) with 'ab' is 3 bytes, and a VARCHAR(255) with 'ab' is 3 bytes. It's the same, but with the lenght limit :)
This will have no effect on performance. In this case the constraint merely helps ensure data integrity.
If you set it to 20, it will save only the first 20 characters. So yes, it will take up less space than 255 characters :).
The required storage space for VARCHAR is as follows:
VARCHAR(L), VARBINARY(L) — L + 1 bytes if column values require 0 – 255 bytes, L + 2 bytes if values may require more than 255 bytes
So VARCHAR does only require the space for the string plus one or two additional bytes for the length of the string.
One of the things that always worries me in MySQL is that my string fields will not be large enough for the data that need to be stored. The PHP project I'm currently working on will need to store strings, the lengths of which may vary wildly.
Not being familiar with how MySQL stores string data, I'm wondering if it would be overkill to use a larger data type like TEXT for strings that will probably often be less than 100 characters. What does MySQL do with highly variable data like this?
See this: http://dev.mysql.com/doc/refman/5.1/en/storage-requirements.html
VARCHAR(M), VARBINARY(M) L + 1 bytes
if column values require 0 – 255
bytes, L + 2 bytes if values may
require more than 255 bytes
BLOB, TEXT L + 2 bytes, where L < 2^16
So in the worst case, you're using 1 byte per table cell more when using TEXT.
As for indexing: you can create a normal index on a TEXT column, but you must give a prefix length - e.g.
CREATE INDEX part_of_name ON customer (name(10));
and moreover, TEXT columns allow you to create and query fulltext indexes if using the MyISAM engine.
On the other hand, TEXT columns are not stored together with the table, so performance could, theoretically, become an issue in some cases (benchmark to see about your specific case).
In recent versions of MySQL, VARCHAR fields can be quite long - up to 65,535 characters depending on character set and the other columns in the table. It is very efficient when you have varying length strings. See:
http://dev.mysql.com/doc/refman/5.1/en/char.html
If you need longer strings than that, you'll probably just have to suck it up and use TEXT.