[jira] [Comment Edited] (OAK-5253) Optimize AbstractBlob#equal to not do content equals when possible

["Julian Sedding (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-5253?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15735027#comment-15735027 ] 

Julian Sedding edited comment on OAK-5253 at 12/9/16 12:16 PM:
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Thanks [~amitjain]. I am wondering if we could compare {{Blob#getReference()}}, but the contract is not very clear regarding its equality semantics. Basically I believe that we need to use something that is delegated to the {{BlobStore}} implementation.

A change in {{SegmentBlob}} would suffer from the same problem as a change in {{AbstractBlob}}. It is backed by an arbitrary {{BlobStore}} implementation, thus we cannot rely on the semantics of {{Blob#getContentIdentity()}}, as it may change depending on the backing {{BlobStore}}.

I have [posted on the mailing list|http://jackrabbit.markmail.org/thread/mzwgde4v7r2xq6yu] to see if someone can clarify whether {{Blob#getReference()}} is suited.


was (Author: jsedding):
Thanks [~amitjain]. I am wondering if we could compare {{Blob#getReference()}}, but the contract is not very clear regarding its equality semantics. Basically I believe that we need to use something that is delegated to the {{BlobStore}} implementation.

A change in {{SegmentBlob}} would suffer from the same problem as a change in {{AbstractBlob}}. It is backed by an arbitrary {{BlobStore}} implementation, thus we cannot rely on the semantics of {{Blob#getContentIdentity()}}, as it may change depending on the backing {{BlobStore}}.

I have posted on the mailing list to see if someone can clarify whether {{Blob#getReference()}} is suited.

> Optimize AbstractBlob#equal to not do content equals when possible
> ------------------------------------------------------------------
>
>                 Key: OAK-5253
>                 URL: https://issues.apache.org/jira/browse/OAK-5253
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: blob
>            Reporter: Amit Jain
>            Assignee: Amit Jain
>             Fix For: 1.6, 1.5.16, 1.4.11
>
>         Attachments: OAK-5253.1.patch
>
>
> AbstractBlob#equals tries to match content when length is equal and content identities is not null and different. Matching content triggers an expensive download of binaries for S3DataStore.
> Since, right now the content identity is the content hash the check can be short -circuited when the content identities is not null and not equal to return false.
> This can be revisited if we change the identity to something different.



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