DBAL-1102: [GH-764] [DBAL-1063] Allow defining duplicate indexes on a table

[doctrinebot]

Jira issue originally created by user @doctrinebot:

This issue is created automatically through a Github pull request on behalf of deeky666:

Url: #764

Message:

This PR removes silent dropping of "duplicate" indexes on a table if two indexes fulfill each other or one overrules the other.
This is necessary to make detection of renamed indexes work properly (introduced in 2.5). Currently there are situations where false positive index renamings are detected because of race conditions.

_Example_

An ORM entity contains an association which adds a foreign key constraint to the underlying table. Foreign key constraints always create implicit indexes on the particular columns.
The entity also contains a mapping for a custom named index fulfilling the foreign key column(s).
The ORM schema tool first adds the foreign key constraint to the table, implicitly creating an index. Afterwards it adds the custom named index which is dropped silently by the table instance because it is considered a "duplicate".
So the table instance created by the schema now contains the auto generated index but not the custom named one.
When using the schema tool to update the schema, the DBAL schema manager is utilized to create the "online" schema. The schema manager detects two indexes in the database, the auto generated one and the custom named one (manually created by the user).
When the schema manger creates the table instance it eventually adds the custom named index first which results in the auto generated index being dropped silently.
When comparing both "offline" and "online" schema, the comparator detects an index rename which actually is none.
This leads to failing DROP INDEX and CREATE INDEX SQL.

Besides this issue "duplicate" indexes are totally legit and DBAL should not decide whether or not to create an index. This should be user responsibility.

This implementation is much more transparent and less error prone and opens up more flexibility for the user to define indexes on tables.

/cc @flack @Ocramius @beberlei

[doctrinebot]

• relates to DBAL-1063: Exceptions from SchemaTool when running with DBAL 2.5.0
• is referenced by DBAL-1108: [GH-769] Allow overriding implicit indexes

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-743] was closed:
#743

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-743] was assigned:
#743

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-764] was assigned:
#764

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-764] was merged:
#764

[doctrinebot]

Issue was closed with resolution "Fixed"

[github-actions]

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