Again: MySQL error: Specified key was too long; max key length is 767 bytes

[Ramblurr]

#455 is back in 3.6.0 (or earlier?) affecting mysql <= 4.6..

mysql <= 4.6 has a max key length of 767 bytes (whereas >= 4.7 has a limit of 3072 bytes)

Caused by: org.polyjdbc.core.exception.SchemaManagerException: [DDL_ERROR] Failed to run DDL:
CREATE INDEX jv_commit_property_property_name_property_value_idx ON jv_commit_property(property_name,property_value(200))
    at org.polyjdbc.core.schema.SchemaManagerImpl.ddl(SchemaManagerImpl.java:91)
    at org.polyjdbc.core.schema.SchemaManagerImpl.create(SchemaManagerImpl.java:52)
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Specified key was too long; max key length is 767 bytes

The property value index has a length of 200 here. Should it be 191 instead?

    RelationBuilder relationBuilder = schema.addRelation(tableName.nameWithSchema());
        relationBuilder
            .primaryKey(tableName.localName() + "_pk").using(COMMIT_PROPERTY_COMMIT_FK, COMMIT_PROPERTY_NAME).and()
            .withAttribute().string(COMMIT_PROPERTY_NAME).withMaxLength(190).and() /// <-------
            .withAttribute().string(COMMIT_PROPERTY_VALUE).withMaxLength(600).and(); /// <------
        foreignKey(tableName, COMMIT_PROPERTY_COMMIT_FK, getCommitTableNameWithSchema(), COMMIT_PK, relationBuilder);
        relationBuilder.build();

        columnsIndex(tableName, schema, COMMIT_PROPERTY_COMMIT_FK);

        // Add index prefix length for MySql
        if (dialect instanceof MysqlDialect) {
            columnsIndex(tableName, schema, new IndexedCols(
                    new String[]{COMMIT_PROPERTY_NAME, COMMIT_PROPERTY_VALUE},
                    new int[]{0, 200})); // <--------------
        }
        else {
            columnsIndex(tableName, schema, COMMIT_PROPERTY_NAME, COMMIT_PROPERTY_VALUE);
        }

1. The col COMMIT_PROPERTY_NAME has max length of 190, and a prefix length of 0 for the index
2. The col COMMIT_PROPERTY_VALUE has a max length of 600, and a prefix length of 200 for the index.

Why is the prefix length 0 for PROPERTY_NAME? This effectively makes the index useless? Or does 0 mean it indexes the entire length.

But for COMMIT_PROPERTY_VALUE the maximum prefix length is 767 / 4 = 191 in mysql 4.6 and 3072 / 4 = 768 in mysql 4.7

[bartoszwalacik]

effective DDL is:

CREATE TABLE `jv_commit_property` (
  `property_name` varchar(190) NOT NULL,
  `property_value` varchar(600) DEFAULT NULL,
  `commit_fk` bigint(20) NOT NULL,
  PRIMARY KEY (`commit_fk`,`property_name`),
  KEY `jv_commit_property_commit_fk_idx` (`commit_fk`),
  KEY `jv_commit_property_property_name_property_value_idx` (`property_name`,`property_value`(200)),
  CONSTRAINT `jv_commit_property_commit_fk` FOREIGN KEY (`commit_fk`) REFERENCES `jv_commit` (`commit_pk`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

So 0 means no prefix for this col.

The bug is not back but have never been fixed.
Fix done in #455 was the move in the right direction but we forgot about indexes.

I will change JaVers code to generate the following DDL:

...
`property_name` varchar(191) NOT NULL,
...
  KEY `jv_commit_property_property_name_property_value_idx` (`property_name`,`property_value`(191))
...

[bartoszwalacik]

@Ramblurr do you think it's ok now? https://github.com/javers/javers/pull/598/files

[bartoszwalacik]

fixed in 3.6.3