I'm using MardiaDB and i'm wondering if there is a way how to install a 'recycle bin' on my server where if someone deleted a table or anything it gets shifted to the recycle bin and restoring it is easy.
Not talking about mounting things to restore it and all that stuff but litterly a 'save place' where it gets stored (i have more then enough space) until i decide to delete it or just keep it there for 24 hours.
Any thoughts?
No such feature exists. http://bugs.mysql.com takes "feature requests".
Such a feature would necessarily involve MySQL; it cannot be done entirely in the OS's filesystem. This is because a running mysql caches information in RAM that the FS does not know about. And because the information about a table/db/proc/trigger/etc is not located entirely in a single file. Instead extra info exists in other, more general, files.
With MyISAM, your goal was partially possible in the fs. A MyISAM table was composed of 3 files: .frm, .MYD',.MYI`. Still MySQL would need to flush something to forget that it know about the table before the fs could move the 3 files somewhere else. MyISAM is going away; so don't even think about using that 'Engine'.
In InnoDB, a table is composed of a .ibd file (if using file_per_table) plus a .frm file, plus some info in the communal ibdata1 file. If the table is PARTITIONed, the layout is more complex.
In version 8.0, most of the previous paragraph will become incorrect -- a major change is occurring.
"Transactions" are a way of undoing writes to a table...
BEGIN;
INSERT/UPDATE/DELETE/etc...
if ( change-mind )
then ROLLBACK;
else COMMIT;
Effectively, the undo log acts as a recycle bin -- but only at the record level, and only until you execute COMMIT.
MySQL 8.0 will add the ability to have DDL statements (eg, DROP TABLE) in a transaction. But, again, it is only until COMMIT.
Think of COMMIT as flushing the recycle bin.
Related
I have a MySQL database in my production environment.Which had about 430 million row, of which 190 million rows were not of any use, so I started deleting these rows range by range, in night, as it would have affected my apps performance in daytime.
Now when I am seeing in my monitoring app, I am seeing 100%IO, of which maximum is write (12-30MB/s). (400-500 writes/sec)
But when I am checking process list I don't find any INSERT or UPDATE query or any rollback.
What can be the possible issue or how can I find any hidden query which may be writing in MySQL.
(In IOTP, I found that write operations are being done by mysqld only)
One more thing, I can see write with 80MB/s in IOTOP , but when I am checking directory size in / , I don't see any rise in any directory size.
Back away slowly... and wait.
InnoDB doesn't change the actual data in the tablespace files with each DML query.
It writes the changes to memory, of course, and then the redo log, at which point they are effectively "live" and safely persisted to disk... but they are not yet applied to the actual data (tablespace) files. InnoDB then syncs the changes to the data files in the background but in the mean time, other queries use a combination of the tablespace and log contents to determine what the "official" table data currently contains. This is, of course, an oversimplification, but MVCC necessarily means the physical data is a superset, though not necessarily a proper superset, of the logical data.
That's very likely to be the explanation for what you are seeing now.
It makes sense that free/used disk space isn't changing, because finalizing the deletion of those rows will only really be marking the space inside the tablespace files as unused. They shouldn't grow or shrink.
Resist the temptation to try to "fix" it and whatever you do, don't restart the server... because the best possible outcome is that it will pick up where it left off because it still has work to do.
SHOW ENGINE INNODB STATUS takes some practice to interpret but will likely be another key to the puzzle.
Is the delete operation still undergoing? DELETE can be extremely slow and generate a lot of writes. It is often better to create a new identical table and copy the rows you want to KEEP over to it and then switch it with the production table instead of delete stuff in the production table directly.
If the DELETE has already finished and you suspect that there are other queries running, you can enable query log for a few seconds and see which queries are executed:
TRUNCATE TABLE mysql.general_log;
SET GLOBAL log_output = 'TABLE';
SET GLOBAL general_log = 'ON';
SELECT SLEEP(10);
SET GLOBAL general_log = 'OFF';
Then SELECT from mysql.general_log to see which queries executed during the 10 seconds sleep.
I need your advice. Need to reclaim disk space on live server with minimum downtime. We are using:
mysql -- 5.5
innodb table per file -- on
Was a huge table(70% insers/30% deletes -- it means that sometimes we delete rows from this table), this table was dropped with "drop table" command, as we expect, mysql didn't release disk space to OS, but now we need to release free space. OPTIMIZE command is possible way -- but now we don't 100% sure if we will have enough free space on disk to do this command, because previous table was huge. But in mysql documentation written:
You can run OPTIMIZE TABLE to compact or recreate a file-per-table tablespace. When you run an OPTIMIZE TABLE, InnoDB creates a new .ibd file with a temporary name, using only the space required to store actual data. When the optimization is complete, InnoDB removes the old .ibd file and replaces it with the new one.
I highlighted confusing moment in documentation, does it means, that "OPTIMIZE dropped_table;" will use only space for data that really needed, for this situation there is no actual data if we drop table early ?
If the table was created when innodb_file_per_table was OFF, then the table was written to ibdata1, and the space is not returned to the OS by DROP TABLE.
If it had been ON, then there would be a .ibd file. Did you see that file before the DROP? Does it still exist? (It should not still exist.)
When DROP removes the .ibd file, there is a slight lag (depending on the OS) while waiting for the data to be actually freed up by the OS. du and/or df reflects this lag.
OPTIMIZE TABLE will copy the table to tmpdir (I think), then drop the old table and play RENAME games. This requires extra space -- enough for a compete copy of the table. Assuming you really have a .ibd file, it will create another .ibd file (with a temp name) and shuffle files. If tmpdir points to a different "filesystem", the shuffle will involve a copy, not just a move.
If I have not explained things adequately, please provide more details -- actual commands you are proposing, size of table in question, whether the .ibd exists, etc.
Mysql 5.05 that is hosting an older application that still gets lots of love from the users. Unfortunately, I'm not anything other than a hack dba at best, and am very hesitant in my skills to safely migrate to a new version of the database unless absolutely necessary. We are in the process of procuring a new application to take over responsibilities for the old application, but are probably a year out or so.
Anyway, I was patching the application the other day and added a column to a table, the command took a while to complete and in the meantime nearly filled up my drive hosting the datafiles. (table is roughly 25G) I believe this was a function of the creation of a temporary table. For reasons I'm not clear on, the space did not become free again after the column was added; i.e., I lost roughly 25G of disk space. I believe (?) this was due to the fact that the database was created with a single datafile; I'm not really sure on the whys, but I do know that I had to free up some space elsewhere to get the drive to an operable state.
That all being said, I've got the column added, but it is worthless to the application without an index. I held off adding the index trying to figure out if it is going to create another massive, persistent 'temporary' table at index creation time. Can anyone out there give me insight into:
Will a create index and or alter table create index statement result in the creation of a temporary table the same size as the existing table?
How can I recover the space that got added to ibdata1 when I added the column?
Any and all advice is greatly appreciated.
MySQL prior to version 5.1 adds/removes indices on InnoDB tables by building temporary tables. It's very slow and expensive. The only way around this is to either upgrade MySQL to 5.1, or to dump the table with e.g. mysqldump, drop it, recreate it with the new indices, and then restore it from the dump.
You can't shrink ibdata1 at all. Your only solution is to rebuild from scratch. It is possible to configure MySQL so it doesn't use one giant ibdata1 file for all the databases - read that answer and it will explain how to configure MySQL/InnoDB so this doesn't happen again, and also how to safely dump and recreate all your databases.
Ultimately, you probably want to
Make a complete dump of your database
Upgrade to MySQL 5.1 or newer
Turn on InnoDB one-file-per-table mode
Restore the dump.
Is there any methods to retrieve deleted records from a mysql database?
No.
Deleted records are gone (or munged so badly you can't recover them). If you have autocommit turned on, the system commits each statement as you complete it (if you have auto commit turned off, then do a rollback NOW - phew, you're saved -- but you are running with autocommit, aren't you?).
One other approach is to reply the activity that created the missing records - can you do that? You can either re-run whatever programs did the updates, or replay them from a binary log (if you still have the binary log). That may not be possible, of course.
So you need to recover the data from somewhere - either a backup of your db (made using mysqldump) or of your file system (the data files of MyISAM tables are all simply structured and on the disk - recovering InnoDB tables are complicated by the shared use of ibdata files).
There is a possible way to retrieve deleted records (depending upon your situation). Please check here:
https://stackoverflow.com/a/72303235/2546381
if i write delete * from tablename in mysql ,all rows get delete it there any way to get the data back in mysql in that table
No, there isn't.
And the correct query is DELETE FROM tablename. (without *)
Restore from backup.
Depends, depends, depends.
I assume you don't have backups. If you do it's better to restore the table from the backup as it was pointed out before.
If the table was MyISAM , then the answer is rather NO than YES. The matter is MyISAM stores data in blocks. The normal block's header is 3 or 4 bytes. The deleted block's header is 20 bytes. So even if you extract records from MYD file the first column (which is your PK in most of cases) will be overwritten. To extract records from MYD file is almost impossible.
If InnoDB, chance is much higher. If MySQL was stopped/killed right after the accident then the chance is close too 100%. InnoDB doesn't delete right away. It marks the records as deleted and will physically purge the records when InnoDB rebuilds B+tree index (read - when you insert new records). So, you have some time. The first thing you'd do in cases like that is stop MySQL immediately, either gracefully or kill -9.
I don't know if I may insert URLs here. Google percona data recovery tool, take the latest revision from the trunk and check mysqlperformance blog (again, google it) for recipes.
Good luck.
UPDATE: Data recovery toolkit moved to GitHub
the easiest way would be to restore your latest backup.