IBX-1467: Fixed OOM regression during Subtree copying

[barw4]

Question	Answer
JIRA issue	IBX-1467
Type	bug
Target eZ Platform version	v2.5
BC breaks	no

Aliases should be now unique which would fix the OOM problems.

Original PR: #3127

Checklist:

• Provided PR description.
• Tested the solution manually.
• Provided automated test coverage.
• Checked that target branch is set correctly (master for features, the oldest supported for bugs).
• Ran PHP CS Fixer for new PHP code (use $ composer fix-cs).
• Asked for a review (ping @ezsystems/engineering-team).

[Steveb-p]

@barw4 could you explain why the array receives duplicate entries in the first place?

From what I see, if a duplicate identifier is detected, the whole foreach loop is skipped.

EDIT: Ok, I've reviewed the code that actually does the merger and I understand now why it happens.

I'd propose to switch to a different approach, which will also be quite a bit faster in terms of checking that identifier exists in the array: let's use hashmap instead.

Currently, $alreadyGeneratedAliases is an array of strings (array<int, string>). If we change it to an associative array with identifiers as keys (array<string, true>), then you could use isset($alreadyGeneratedAliases[$identifier] to check that an entry already exists (instead of in_array) and push a value into $alreadyGeneratedAliases by using $alreadyGeneratedAliases[$identifier] = true.

This will change the complexity of check from o(n) to o(1) and allow array_merge to work properly.

[Steveb-p]

My proposal is in a separate comment.

[Steveb-p]

@ViniTou substantial change to the original solution, hence re-request for review.

[tomaszszopinski]

QA approved on eZPlatform 2.5.

[barw4]

Merged into:
1.3: ezsystems/ezplatform-kernel@104098a
ibexa/core/main: ibexa/core#27