What are problems occur when mysql server table contains more than 120 columns ?
from a technical point of view without any consideration on the reasons for which you need 120 columns in a table mysql documentation 5.7 says:
Column Count Limits
MySQL has hard limit of 4096 columns per table, but the effective
maximum may be less for a given table.
https://dev.mysql.com/doc/refman/5.7/en/column-count-limit.html
This is bad practice to have 120 columns in a table better to split into multiple tables.
Since MYSQL is famous for relation database, So make relation based tables structure.
List of issues comes once your application become bigger.
Application gets slow (Since data fetching from table is slowly).
If your internet is slow, then you may not load the application page.
If huge amount of data is loaded at once due to the numbers of columns, then your server require more bandwidth.
Might you may not able you open in mobile, Since mobile better work with small amount of data.
https://dba.stackexchange.com/questions/3972/too-many-columns-in-mysql
There is a hard limit of 4096 columns per table, but the effective maximum may be less for a given table. The exact limit depends on several interacting factors.
Every table (regardless of storage engine) has a maximum row size of 65,535 bytes. Storage engines may place additional constraints on this limit, reducing the effective maximum row size.
The maximum row size constrains the number (and possibly size) of columns because the total length of all columns cannot exceed this size.
...
Individual storage engines might impose additional restrictions that limit table column count. Examples:
InnoDB permits up to 1000 columns.
Related
What is the upper limit of records for MySQL database table. I'm wondering about autoincrement field. What would happen if I add milions of records? How to handle this kind of situations?
Thx!
The greatest value of an integer has little to do with the maximum number of rows you can store in a table.
It's true that if you use an int or bigint as your primary key, you can only have as many rows as the number of unique values in the data type of your primary key, but you don't have to make your primary key an integer, you could make it a CHAR(100). You could also declare the primary key over more than one column.
There are other constraints on table size besides number of rows. For instance you could use an operating system that has a file size limitation. Or you could have a 300GB hard drive that can store only 300 million rows if each row is 1KB in size.
The limits of database size is really high:
http://dev.mysql.com/doc/refman/5.1/en/source-configuration-options.html
The MyISAM storage engine supports 232 rows per table, but you can build MySQL with the --with-big-tables option to make it support up to 264 rows per table.
http://dev.mysql.com/doc/refman/5.1/en/innodb-restrictions.html
The InnoDB storage engine has an internal 6-byte row ID per table, so there are a maximum number of rows equal to 248 or 281,474,976,710,656.
An InnoDB tablespace also has a limit on table size of 64 terabytes. How many rows fits into this depends on the size of each row.
The 64TB limit assumes the default page size of 16KB. You can increase the page size, and therefore increase the tablespace up to 256TB. But I think you'd find other performance factors make this inadvisable long before you grow a table to that size.
mysql int types can do quite a few rows: http://dev.mysql.com/doc/refman/5.0/en/numeric-types.html
unsigned int largest value is 4,294,967,295
unsigned bigint largest value is 18,446,744,073,709,551,615
I suggest, never delete data. Don't say if the tables is longer than 1000 truncate the end of the table. There needs to be real business logic in your plan like how long has this user been inactive. For example, if it is longer than 1 year then put them in a different table. You would have this happen weekly or monthly in a maintenance script in the middle of a slow time.
When you run into to many rows in your table then you should start sharding the tables or partitioning and put old data in old tables by year such as users_2011_jan, users_2011_feb or use numbers for the month. Then change your programming to work with this model. Maybe make a new table with less information to summarize the data in less columns and then only refer to the bigger partitioned tables when you need more information such as when the user is viewing their profile. All of this should be considered very carefully so in the future it isn't too expensive to re-factor. You could also put only the users which comes to your site all the time in one table and the users that never come in an archived set of tables.
In InnoDB, with a limit on table size of 64 terabytes and a MySQL row-size limit of 65,535 there can be 1,073,741,824 rows. That would be minimum number of records utilizing maximum row-size limit. However, more records can be added if the row size is smaller .
According to Scalability and Limits section in http://dev.mysql.com/doc/refman/5.6/en/features.html,
MySQL support for large databases. They use MySQL Server with databases that contain 50 million records. Some users use MySQL Server with 200,000 tables and about 5,000,000,000 rows.
Row Size Limits
The maximum row size for a given table is determined by several factors:
The internal representation of a MySQL table has a maximum row size
limit of 65,535 bytes, even if the storage engine is capable of
supporting larger rows. BLOB and TEXT columns only contribute 9 to 12
bytes toward the row size limit because their contents are stored
separately from the rest of the row.
The maximum row size for an InnoDB table, which applies to data
stored locally within a database page, is slightly less than half a page. For example, the maximum row size is slightly less than 8KB for the default 16KB InnoDB page size, which is defined by the innodb_page_size configuration option. “Limits on InnoDB Tables”.
If a row containing variable-length columns exceeds the InnoDB maximum row size, InnoDB selects variable-length columns for external off-page storage until the row fits within the InnoDB row size limit.
The amount of data stored locally for variable-length columns that are
stored off-page differs by row format. For more information, see
“InnoDB Row Storage and Row Formats”.
Different storage formats use different amounts of page header and trailer data, which affects the amount of storage available for rows.
Link http://dev.mysql.com/doc/refman/5.7/en/column-count-limit.html
Row Size Limits
The maximum row size for a given table is determined by several factors:
The internal representation of a MySQL table has a maximum row size limit of 65,535 bytes, even if the storage engine is capable of supporting larger rows. BLOB and TEXT columns only contribute 9 to 12 bytes toward the row size limit because their contents are stored separately from the rest of the row.
The maximum row size for an InnoDB table, which applies to data stored locally within a database page, is slightly less than half a page for 4KB, 8KB, 16KB, and 32KB innodb_page_size settings. For example, the maximum row size is slightly less than 8KB for the default 16KB InnoDB page size. For 64KB pages, the maximum row size is slightly less than 16KB. See Section 15.8.8, “Limits on InnoDB Tables”.
If a row containing variable-length columns exceeds the InnoDB maximum row size, InnoDB selects variable-length columns for external off-page storage until the row fits within the InnoDB row size limit. The amount of data stored locally for variable-length columns that are stored off-page differs by row format. For more information, see Section 15.11, “InnoDB Row Storage and Row Formats”.
Different storage formats use different amounts of page header and trailer data, which affects the amount of storage available for rows.
For information about InnoDB row formats, see Section 15.11, “InnoDB Row Storage and Row Formats”, and Section 15.8.3, “Physical Row Structure of InnoDB Tables”.
For information about MyISAM storage formats, see Section 16.2.3, “MyISAM Table Storage Formats”.
http://dev.mysql.com/doc/refman/5.7/en/innodb-restrictions.html
There is no limit. It only depends on your free memory and system maximum file size. But that doesn't mean you shouldn't take precautionary measure in tackling memory usage in your database. Always create a script that can delete rows that are out of use or that will keep total no of rows within a particular figure, say a thousand.
There are 210 columns in my table with around 10000 rows. Each row is unique and there is a primary key on the table. The thing is we always had to do select all query on the table to get data of all the sites.
Currently, the problem is it takes too much time and the data returned is around 10mb and it will be large in the future.
The table has varchar, text and date types in it.
Is there any way I can modify the structure or something to make my retrieval faster. More indexing or breaking down the table. (Although I think denormalized data is good for retrieval)
Update: "why do wider tables slow down the query performance?"
Thanks..!
why do wider tables slow down the query performance?
InnoDB stores "wide" tables in a different way. Instead of having all the columns together in a single string (plus overhead, such as lengths, etc), it does the following:
If the total of all the columns for a given row exceeds about 8KB, it will move some of the data to another ("off-record") storage area.
Which columns are moved off-record depends on the sizes of the columns, etc.
The details depend on the ROW_FORMAT chosen.
"Off-record" is another 16KB block (or blocks).
Later, when doing SELECT * (or at least fetching the off-record column(s)), it must do another disk fetch.
What to do?
Rethink having so many columns.
Consider "vertical partitioning", wherein you have another table(s) that contains selected TEXT columns. Suggest picking groups of columns based on access patterns in your app.
For columns that are usually quite long, consider compressing them in the client and storing into a BLOB instead of a TEXT. Most "text" shrinks 3:1. Blobs are sent off-record the same as Texts, however, these compressed blobs would be smaller, hence less likely to spill.
Do more processing in SQL -- to avoid returning all the rows, or to avoid returning the full text, etc. When blindly shoveling lots of text to a client, the network and client become a sighificant factor in the elapsed time, not just the SELECT, itself.
What is the upper limit of records for MySQL database table. I'm wondering about autoincrement field. What would happen if I add milions of records? How to handle this kind of situations?
Thx!
The greatest value of an integer has little to do with the maximum number of rows you can store in a table.
It's true that if you use an int or bigint as your primary key, you can only have as many rows as the number of unique values in the data type of your primary key, but you don't have to make your primary key an integer, you could make it a CHAR(100). You could also declare the primary key over more than one column.
There are other constraints on table size besides number of rows. For instance you could use an operating system that has a file size limitation. Or you could have a 300GB hard drive that can store only 300 million rows if each row is 1KB in size.
The limits of database size is really high:
http://dev.mysql.com/doc/refman/5.1/en/source-configuration-options.html
The MyISAM storage engine supports 232 rows per table, but you can build MySQL with the --with-big-tables option to make it support up to 264 rows per table.
http://dev.mysql.com/doc/refman/5.1/en/innodb-restrictions.html
The InnoDB storage engine has an internal 6-byte row ID per table, so there are a maximum number of rows equal to 248 or 281,474,976,710,656.
An InnoDB tablespace also has a limit on table size of 64 terabytes. How many rows fits into this depends on the size of each row.
The 64TB limit assumes the default page size of 16KB. You can increase the page size, and therefore increase the tablespace up to 256TB. But I think you'd find other performance factors make this inadvisable long before you grow a table to that size.
mysql int types can do quite a few rows: http://dev.mysql.com/doc/refman/5.0/en/numeric-types.html
unsigned int largest value is 4,294,967,295
unsigned bigint largest value is 18,446,744,073,709,551,615
I suggest, never delete data. Don't say if the tables is longer than 1000 truncate the end of the table. There needs to be real business logic in your plan like how long has this user been inactive. For example, if it is longer than 1 year then put them in a different table. You would have this happen weekly or monthly in a maintenance script in the middle of a slow time.
When you run into to many rows in your table then you should start sharding the tables or partitioning and put old data in old tables by year such as users_2011_jan, users_2011_feb or use numbers for the month. Then change your programming to work with this model. Maybe make a new table with less information to summarize the data in less columns and then only refer to the bigger partitioned tables when you need more information such as when the user is viewing their profile. All of this should be considered very carefully so in the future it isn't too expensive to re-factor. You could also put only the users which comes to your site all the time in one table and the users that never come in an archived set of tables.
In InnoDB, with a limit on table size of 64 terabytes and a MySQL row-size limit of 65,535 there can be 1,073,741,824 rows. That would be minimum number of records utilizing maximum row-size limit. However, more records can be added if the row size is smaller .
According to Scalability and Limits section in http://dev.mysql.com/doc/refman/5.6/en/features.html,
MySQL support for large databases. They use MySQL Server with databases that contain 50 million records. Some users use MySQL Server with 200,000 tables and about 5,000,000,000 rows.
Row Size Limits
The maximum row size for a given table is determined by several factors:
The internal representation of a MySQL table has a maximum row size
limit of 65,535 bytes, even if the storage engine is capable of
supporting larger rows. BLOB and TEXT columns only contribute 9 to 12
bytes toward the row size limit because their contents are stored
separately from the rest of the row.
The maximum row size for an InnoDB table, which applies to data
stored locally within a database page, is slightly less than half a page. For example, the maximum row size is slightly less than 8KB for the default 16KB InnoDB page size, which is defined by the innodb_page_size configuration option. “Limits on InnoDB Tables”.
If a row containing variable-length columns exceeds the InnoDB maximum row size, InnoDB selects variable-length columns for external off-page storage until the row fits within the InnoDB row size limit.
The amount of data stored locally for variable-length columns that are
stored off-page differs by row format. For more information, see
“InnoDB Row Storage and Row Formats”.
Different storage formats use different amounts of page header and trailer data, which affects the amount of storage available for rows.
Link http://dev.mysql.com/doc/refman/5.7/en/column-count-limit.html
Row Size Limits
The maximum row size for a given table is determined by several factors:
The internal representation of a MySQL table has a maximum row size limit of 65,535 bytes, even if the storage engine is capable of supporting larger rows. BLOB and TEXT columns only contribute 9 to 12 bytes toward the row size limit because their contents are stored separately from the rest of the row.
The maximum row size for an InnoDB table, which applies to data stored locally within a database page, is slightly less than half a page for 4KB, 8KB, 16KB, and 32KB innodb_page_size settings. For example, the maximum row size is slightly less than 8KB for the default 16KB InnoDB page size. For 64KB pages, the maximum row size is slightly less than 16KB. See Section 15.8.8, “Limits on InnoDB Tables”.
If a row containing variable-length columns exceeds the InnoDB maximum row size, InnoDB selects variable-length columns for external off-page storage until the row fits within the InnoDB row size limit. The amount of data stored locally for variable-length columns that are stored off-page differs by row format. For more information, see Section 15.11, “InnoDB Row Storage and Row Formats”.
Different storage formats use different amounts of page header and trailer data, which affects the amount of storage available for rows.
For information about InnoDB row formats, see Section 15.11, “InnoDB Row Storage and Row Formats”, and Section 15.8.3, “Physical Row Structure of InnoDB Tables”.
For information about MyISAM storage formats, see Section 16.2.3, “MyISAM Table Storage Formats”.
http://dev.mysql.com/doc/refman/5.7/en/innodb-restrictions.html
There is no limit. It only depends on your free memory and system maximum file size. But that doesn't mean you shouldn't take precautionary measure in tackling memory usage in your database. Always create a script that can delete rows that are out of use or that will keep total no of rows within a particular figure, say a thousand.
I am wondering at which point would my MySQL table be considered too big.
The table is this:
id
customer_id (int)
value (float)
timestamp_1 (datetime)
tmestampt_2 (datetime)
so the row size is not too great, but would be constantly being added. In my estimation I am looking at around 17000 new rows a day, so about 500,000 a month. The data is likely to be polled quite constantly in large quantities.
Should I be looking at ways to split this or am I still OK at this point?
Thanks,
From http://dev.mysql.com/doc/refman/5.0/en/full-table.html:
The effective maximum table size for MySQL databases is usually determined by operating system constraints on file sizes, not by MySQL internal limits.
From the table in the linked article, on FAT/FAT32 systems and Linux pre 2.4, the maximum file size is 2-4 GB, on all other systems listed, the max file size is at least 2TB.
So long as you index your table correctly, there shouldn't be too much slowdown as your table grows. However, if your table grows to the extent that you do notice any slowdown, it might be an option for you to archive off old records periodically.
What is "Too big" is really going to depend on how big your hardware is. MySQL itself should have no problem managing millions of rows in a table.
Still, I would think about splitting it up to get the best possible performance. Exactly how you do that would depend on how the data is used. Is more recent data used much more frequently? If so, create an archive table with the same structure to store the old data and periodically move data from your main table to the archive table. This would increase the complexity of your application, but could give you better performance in the long run.
It would be too big when your query starts to slow down.
Do you need to keep the entire history in this table or are you only ever looking for the latest values? You could optimise things by archiving off records you don't need onto an archive table.
Other than that, be careful how you plan your indexes. If you put indexes all over the place, inserts may take longer. If you don't have any indexes but need to sort and filter, the retrieval may be too slow.
In MyISAM, the theoretical table size is constrained by the size of data pointer, set by myisam_data_pointer_size.
It can be from 2 to 7 bytes, making the possible table size to be from 2 ^ (8 * 2) = 65k to 2 ^ (8 * 7) = 64P bytes long.
By default, it's 6 bytes (256T).
Of course, since MyISAM tables are held in one file, the maximum size of the file is subject to constraint by the OS and the filesystem.
An InnoDB tablespace can consist of as many as 2^32 pages, which is 4G pages of 16K bytes each, or 64T bytes at most.
What is the maximum size for a MySQL table? Is it 2 million at 50GB? 5 million at 80GB?
At the higher end of the size scale, do I need to think about compressing the data? Or perhaps splitting the table if it grew too big?
I once worked with a very large (Terabyte+) MySQL database. The largest table we had was literally over a billion rows.
It worked. MySQL processed the data correctly most of the time. It was extremely unwieldy though.
Just backing up and storing the data was a challenge. It would take days to restore the table if we needed to.
We had numerous tables in the 10-100 million row range. Any significant joins to the tables were too time consuming and would take forever. So we wrote stored procedures to 'walk' the tables and process joins against ranges of 'id's. In this way we'd process the data 10-100,000 rows at a time (Join against id's 1-100,000 then 100,001-200,000, etc). This was significantly faster than joining against the entire table.
Using indexes on very large tables that aren't based on the primary key is also much more difficult. Mysql stores indexes in two pieces -- it stores indexes (other than the primary index) as indexes to the primary key values. So indexed lookups are done in two parts: First MySQL goes to an index and pulls from it the primary key values that it needs to find, then it does a second lookup on the primary key index to find where those values are.
The net of this is that for very large tables (1-200 Million plus rows) indexing against tables is more restrictive. You need fewer, simpler indexes. And doing even simple select statements that are not directly on an index may never come back. Where clauses must hit indexes or forget about it.
But all that being said, things did actually work. We were able to use MySQL with these very large tables and do calculations and get answers that were correct.
About your first question, the effective maximum size for the database is usually determined by operating system, specifically the file size MySQL Server will be able to create, not by MySQL Server itself. Those limits play a big role in table size limits. And MyISAM works differently from InnoDB. So any tables will be dependent on those limits.
If you use InnoDB you will have more options on manipulating table sizes, resizing the tablespace is an option in this case, so if you plan to resize it, this is the way to go. Give a look at The table is full error page.
I am not sure the real record quantity of each table given all necessary information (OS, Table type, Columns, data type and size of each and etc...) And I am not sure if this info is easy to calculate, but I've seen simple table with around 1bi records in a couple cases and MySQL didn't gave up.