JDBC bugfix: Don't reuse a defunct databaseMetaData

[bbeaudreault]

I'm not sure why databaseMetaData is a static variable. It looks to have been that way since the very beginning. But I recently ran into an issue where if you create multiple VitessConnections and close the first one, all of the other VitessConnections reference what is effectively a defunct databaseMetadata. That is, the databaseMetadata references a connection which is closed, and so nothing can be called on it.

This is very easily reproducible for anyone who uses hikari or other jdbc pooling libraries.

This fixes to ensure we don't re-use such databaseMetadata values. I'd also be happy to make this non-static, if preferred.

@harshit-gangal @ashudeep-sharma

[ashudeep-sharma-zz]

The reason why we made the databaseMetadata as static is because we didn't want to fire the show queries for every connection.

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Review status: 0 of 1 files reviewed at latest revision, 1 unresolved discussion, some commit checks broke.

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java/jdbc/src/main/java/com/flipkart/vitess/jdbc/VitessConnection.java, line 235 at r1 (raw file):

    }

    private boolean metadataNullOrDefunct() throws SQLException {

Please rename this function to metadataNullOrDefunctional().

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Comments from Reviewable

[ashudeep-sharma-zz]

Just a Minor Comment, Rest Looks Good to Me.

[bbeaudreault]

Thanks! Defunctional is not a word, so I renamed to Closed instead -- metadataNullOrClosed

[ashudeep-sharma-zz]

Works for me.

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Reviewed 1 of 1 files at r1.
Review status: 0 of 1 files reviewed at latest revision, 1 unresolved discussion.

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Comments from Reviewable

[ashudeep-sharma-zz]

Thank you so much for fixing it.

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Review status: 0 of 1 files reviewed at latest revision, 1 unresolved discussion.

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Comments from Reviewable

[bbeaudreault]

@sougou @alainjobart @michael-berlin This got a LGTM. Could one of you merge when you get a chance? Looking to submit a dependent PR today. Thanks!