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https://issues.apache.org/jira/browse/CASSANDRA-674?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12797450#action_12797450
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Jonathan Ellis commented on CASSANDRA-674:
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This approach is fine for proof of concept, but be aware that any sstable
format change that we actually commit is going to need to support reading the
old version. So ultimately what a patch set like this needs to look like is
00: provide APIs that CFS et al can use to read data from either old or new
versions (e.g. getScanner, getFileDataInput); probably you will end up with an
AbstractSSTableReader class with common functionality like getColumnComparator
01: refactor old SSTR class and callers to use the new API
02: introduce the new data file format in separate classes
Splitting it up like this is also going to be much much easier to rebase
against the moving target of trunk (and there is enough missing here that it
looks like it's going to need to be rebased for a while).
> New SSTable Format
> ------------------
>
> Key: CASSANDRA-674
> URL: https://issues.apache.org/jira/browse/CASSANDRA-674
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Affects Versions: 0.9
> Reporter: Stu Hood
> Assignee: Stu Hood
> Fix For: 0.9
>
> Attachments: 674-v1.diff
>
>
> Various tickets exist due to limitations in the SSTable file format,
> including #16, #47 and #328. Attached is a proposed design/implementation of
> a new file format for SSTables that addresses a few of these limitations. The
> implementation has a bunch of issues/fixmes, which I'll describe in the
> comments.
> The file format is described in the javadoc for the o.a.c.io.SSTableWriter
> class, but briefly:
> * Blocks are opaque (except for their header) so that they can be
> compressed. The index file contains an entry for the first key in every
> Block. Blocks contain Slices.
> * Slices are series of columns with the same parents and (deletion)
> metadata. They can be used to represent ColumnFamilies or SuperColumns (or a
> slice of columns at any other depth). A single CF can be split across
> multiple Slices, which can be split across multiple blocks.
> * Neither Slices nor Blocks have a fixed size or maximum length, but they
> each have target lengths which can be stretched and broken by very large
> columns.
> The most interesting concepts from this patch are:
> * Block compression is possible (currently using GZIP, which has one bug
> mentioned in the comments),
> * Compaction involves merging intersecting Slices from input SSTables. Since
> large rows will be broken down into multiple slices, only the portions of
> rows that intersect between tables need to be
> deserialized/merged/held-in-memory,
> * Indexes for individual rows are gone, since the global index allows random
> access to the middle of column families that span Blocks, and Slices allow
> batches of columns to be skipped within a Block.
> * Bloom filters for individual rows are gone, and the global filter contains
> ColumnKeys instead, meaning that a query for a column that doesn't exist in a
> row that does will often not need to seek to the row.
> * Metadata (deletion/gc time) and ColumnKeys (key, colname1, colname2...)
> for columns are defined recursively, so deeply nested slices are possible,
> * Slices representing a single parent (CF, SC, etc) can have different
> Metadata, meaning that a tombstone Slice from d-f could sit between Slices
> containing columns a-c and g-h. This allows for eventually consistent range
> deletes of columns.
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