Thesql: slow import

importMySQL

I have a 83GB compressed .sql.gz file that I'm importing. The DB size on the source server (the size of the folder) was 240GB.

I'm importing it on a Amazon cloud server, with 2CPUs, 4GM RAM and SSD disk, using innodb buffer of 2.2GB and max packet of 128MB. The allowed IOPS on the server are 1200. I'm running version 5.5.63 for "legacy reasons".

The import command is like this:

zcat dump.sql.gz | mysql -u root -ppasswd DB_NAME

Most of the volume is due to 4 compressed tables that are also partitioned by timestamp range.

The import is going very slowly. The .ibd files for the compressed tables (or rather, the one that is at that time receiving data) increase at a super-slow rate of 40MB per 5 minute period, as I find using "ls -l" 5 minutes apart. The intriguing thing is that the iostat utility reports that every 5sec between 50MB-140MB are written on disk, here is an example:

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
      33.00    0.00    0.99    2.37   11.86   51.78

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
xvda            657.60         0.00     13877.70          0      69388

So, bottom line, the operating system reports that the disk is seeing a lot of traffic, but the innodb table files are increasing at a snail's pace.

Thanks for any clues as to what is going on.

Best Answer

The only thing you can do to speed up the import without restarting the instance or restarting the import is to do the following:

mysql> SET GLOBAL innodb_flush_log_at_trx_commit = 2;

This will increase the log flushing throughout.

If you have the query cache on, disable it immediately !!!

mysql> SET GLOBAL query_cache_size = 0;
mysql> SET GLOBAL query_cache_tpye = 0;

These are the only things you can do dynamically to speed things up a little.

GIVE IT A TRY !!!

UPDATE 2020-07-17 13:52 EDT

Since you can do restarts, add this to my.cnf

[mysqld]
innodb_doublewrite = 0
innodb_log_buffer_size = 32M

and restart mysqld and then restart the load.

If you have binary logging enabled in the DB, disable the binary logs for the import

zcat dump.sql.gz | mysql -u root -ppasswd DB_NAME --init-command="SET sql_log_bin=0"

When the reload is done, remove innodb_doublewrite = 0 and restart mysqld.

I have suggested disabling the double write buffer before

Dec 19, 2014 : When is it safe to disable InnoDB doublewrite buffering?
Sep 29, 2016 : MySQL settings useful to speed up a mysqldump import

Related Solutions

MySQL Import – How to Import Multiple CSV Fields into One MySQL Field

The following LOAD DATA sentence loads the CSV file, ignoring the first line and inserting into the desired fields, but changing the format of the Date and Time columns into a proper datetime type:

mysql> LOAD DATA INFILE '/tmp/alarms.csv' 
       INTO TABLE alarms 
       COLUMNS TERMINATED BY ',' 
       IGNORE 1 LINES 
       (@Date, @Time, ALARM_01, PT001, TEMP_AMB) 
       SET DateTime = STR_TO_DATE(CONCAT(@Date, ' ', @Time), '%d/%m/%Y %H:%i:%s');
Query OK, 2 rows affected (0.01 sec)
Records: 2  Deleted: 0  Skipped: 0  Warnings: 0

mysql> SELECT * FROM alarms;
+----+---------------------+----------+--------+----------+
| id | DateTime            | ALARM_01 | PT001  | TEMP_AMB |
+----+---------------------+----------+--------+----------+
|  1 | 2014-08-14 14:23:21 |        0 | 130.00 |    20.00 |
|  2 | 2014-08-14 14:23:25 |      101 | 128.09 |    20.10 |
+----+---------------------+----------+--------+----------+
2 rows in set (0.00 sec)

Your fields and datatypes may vary slightly, with no effect on the import query.

MySQL Query Hangs on Import – How to Resolve

I suspect you're suffering 'out-of-the-box' syndrome. For the whole world to know... MySQL config out of the box sucks.

Go to https://tools.percona.com/wizard and create better configuration based on the questions asked in the form. This should provide you with a better starting point. Once the output is generated, add it to your configuration file (/etc/my.cnf) and restart MySQL; review the mysql error log to ensure that your mysql instance started cleanly (beware of paths, permissions and the innodb_log_file_size size differences since that will require disposal of the old ib_log* files before new ones can be created). Once done, try your import again.