MYSQL 8.0 Upgrade &Downgrade的幾點注意

darren__chan發表於2021-10-19
MySql
Important
Downgrade from MySQL 8.0 to MySQL 5.7, or from a MySQL 8.0 release to a previous MySQL 8.0 release, is not supported. The only supported alternative is to restore a backup taken before upgrading. It is therefore imperative that you back up your data before starting the upgrade process.




Upgrade Paths

  • Upgrade from MySQL 5.7 to 8.0 is supported. However, upgrade is only supported between General Availability (GA) releases. For MySQL 8.0, it is required that you upgrade from a MySQL 5.7 GA release (5.7.9 or higher). Upgrades from non-GA releases of MySQL 5.7 are not supported.
  • Upgrading to the latest release is recommended before upgrading to the next version. For example, upgrade to the latest MySQL 5.7 release before upgrading to MySQL 8.0.
  • Upgrade that skips versions is not supported. For example, upgrading directly from MySQL 5.6 to 8.0 is not supported.
  • Once a release series reaches General Availability (GA) status, upgrade within the release series (from one GA version to another GA version) is supported.
Some changes to the responsibility for step 2 occurred in MySQL 8.0.16:
  • Prior to MySQL 8.0.16, upgrades the Performance Schema, the INFORMATION_SCHEMA, and the objects described in step 2. The DBA is expected to invoke   manually after starting the server.
  • As of MySQL 8.0.16, the server performs all tasks previously handled by  . Although upgrading remains a two-step operation, the server performs them both, resulting in a simpler process.
Depending on the version of MySQL to which you are upgrading, the instructions in   and   indicate whether the server performs all upgrade tasks or whether you must also invoke 
When upgrading from MySQL 5.7 to MySQL 8.0, any undo tablespaces that exist in the MySQL 5.7 instance are removed and replaced by two new default undo tablespaces.
Due to a regression introduced in MySQL 8.0.14, in-place upgrade on a case-sensitive file system from MySQL 5.7 or a MySQL 8.0 release prior to MySQL 8.0.14 to MySQL 8.0.16 failed for instances with partitioned tables and [lower_case_table_names=1](). The failure was caused by a case mismatch issue related to partitioned table file names. The fix that introduced the regression was reverted, which permits upgrades to MySQL 8.0.17 from MySQL 5.7 or MySQL 8.0 releases prior to MySQL 8.0.14 to function as normal. However, the regression is still present in the MySQL 8.0.14, 8.0.15, and 8.0.16 releases.





Changed Server Defaults

Option/Parameter
Old Default
New Default
Server changes

latin1
utf8mb4
latin1_swedish_ci
utf8mb4_0900_ai_ci
OFF
ON
16KB
1MB
OFF
ON
-1 (autosize) changed from : back_log = 50 + (max_connections / 5)
-1 (autosize) changed to : back_log = max_connections
4194304 (4MB)
67108864 (64MB)
64
1024
OFF
ON
2000
4000
3 (Notes)
2 (Warning)
InnoDB changes

0
2
OFF
ON
NULL
fsync (Unix), unbuffered (Windows)
1 (consecutive)
2 (interleaved)
1 (enable)
0 (disable)
0 (%)
10 (%)
75 (%)
90 (%)
Performance Schema changes

performance-schema-instrument='wait/lock/metadata/sql/%=ON'
OFF
ON
performance-schema-instrument='memory/%=COUNTED'
OFF
COUNTED
performance-schema-consumer-events-transactions-current=ON
OFF
ON
performance-schema-consumer-events-transactions-history=ON
OFF
ON
performance-schema-instrument='transaction%=ON'
OFF
ON
Replication changes

OFF
ON
0
1
OFF
ON
0
30
FILE
TABLE
FILE
TABLE
OFF
XXHASH64
INDEX_SCAN, TABLE_SCAN
INDEX_SCAN, HASH_SCAN
16M
128M
gtid_executed_compression_period
1000
0
Group Replication changes

0
3
ABORT_SERVER
READ_ONLY
0
5
  1. To check for these issues, execute this command:
mysqlcheck -u root -p --all-databases --check-upgrade
If reports any errors, correct the issues.



Upgrade Troubleshooting

·        A schema mismatch in a MySQL 5.7 instance between the .frm file of a table and the InnoDB data dictionary can cause an upgrade to MySQL 8.0 to fail. Such mismatches may be due to .frm file corruption. To address this issue, dump and restore affected tables before attempting the upgrade again.
·        If problems occur, such as that the new server does not start, verify that you do not have an old my.cnf file from your previous installation. You can check this with the option (for example, ). If this command displays anything other than the program name, you have an active my.cnf file that affects server or client operation.
·        If, after an upgrade, you experience problems with compiled client programs, such as Commands out of sync or unexpected core dumps, you probably have used old header or library files when compiling your programs. In this case, check the date for your mysql.h file and libmysqlclient.a library to verify that they are from the new MySQL distribution. If not, recompile your programs with the new headers and libraries. Recompilation might also be necessary for programs compiled against the shared client library if the library major version number has changed (for example, from libmysqlclient.so.20 to libmysqlclient.so.21).
·        If you have created a loadable function with a given name and upgrade MySQL to a version that implements a new built-in function with the same name, the loadable function becomes inaccessible. To correct this, use to drop the loadable function, and then use to re-create the loadable function with a different nonconflicting name. The same is true if the new version of MySQL implements a built-in function with the same name as an existing stored function. See , for the rules describing how the server interprets references to different kinds of functions.
·        If upgrade to MySQL 8.0 fails due to any of the issues outlined in , the server reverts all changes to the data directory. In this case, remove all redo log files and restart the MySQL 5.7 server on the existing data directory to address the errors. The redo log files (ib_logfile*) reside in the MySQL data directory by default. After the errors are fixed, perform a slow shutdown (by setting ) before attempting the upgrade again.
mysqlcheck --repair --databases _db_name
mysqlcheck --repair --all-databases




Downgrading MySQL

Downgrade from MySQL 8.0 to MySQL 5.7, or from a MySQL 8.0 release to a previous MySQL 8.0 release, is not supported. The only supported alternative is to restore a backup taken  before  upgrading. It is therefore imperative that you back up your data before starting the upgrade process.


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