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From "Jonathan Ellis (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-847) Make the reading half of compactions memory-efficient
Date Sat, 06 Mar 2010 02:03:27 GMT


Jonathan Ellis commented on CASSANDRA-847:

> I've always considered the Iterator interface to be super-weak for IO. There is no support
for exception handling, and hasNext() is dangerous (when you begin chaining iterators that
are returning lazy objects like IteratingRow) because it usually involves seeks. 

Typed exceptions are a misfeature anyway, so that's a non-issue.

hasNext won't seek any more than a clunkier manual interface.  either way you need to (a)
design your format so you don't have to do random i/o and (b) buffer to avoid seeks when switching
between different objects, and that is what we do.

the old iterator-based compaction for instance never does more seeks than another interface
would given the same buffer sizes.

> Make the reading half of compactions memory-efficient
> -----------------------------------------------------
>                 Key: CASSANDRA-847
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Stu Hood
>            Priority: Critical
>             Fix For: 0.7
>         Attachments: 0001-Add-structures-that-were-important-to-the-SSTableSca.patch,
0002-Implement-most-of-the-new-SSTableScanner-interface.patch, 0003-Rename-RowIndexedReader-specific-test.patch,
0004-Improve-Scanner-tests-and-separate-SuperCF-handling-.patch, 0005-Add-Scanner-interface-and-a-Filtered-implementation-.patch,
> This issue is the next on the road to finally fixing CASSANDRA-16. To make compactions
memory efficient, we have to be able to perform the compaction process on the smallest possible
chunks that might intersect and contend one-another, meaning that we need a better abstraction
for reading from SSTables.

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