Improve error for key value size limits

[peterstace]

We now have two separate errors, one for keys and one for values. The error will contain the first 1KB of the offending key/value, and show what the limit was.

Also, the max value size is now the same as the value log size. It's not checked when replaying the value log, since the setting could have been different for a previous run of badger.

I increased the limit for the key size from 1MB to 16MB (found some data in the graph overflow dataset that possibly violates the 1MB limit).

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This change is 

[manishrjain]

Address the comment before submitting.

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Reviewed 3 of 3 files at r1.
Review status: all files reviewed at latest revision, 1 unresolved discussion, some commit checks failed.

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value.go, line 83 at r1 (raw file):

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const maxKeySize = 16 << 20

I think 1MB is good for keys. In comparison, our tables are only 64MB each. If we have some data in SO which violates this, we should avoid the exact index.

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Comments from Reviewable

[peterstace]

Review status: all files reviewed at latest revision, 1 unresolved discussion, some commit checks failed.

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value.go, line 83 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

I think 1MB is good for keys. In comparison, our tables are only 64MB each. If we have some data in SO which violates this, we should avoid the exact index.

Done. Reverted to use 1MB.

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Comments from Reviewable