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https://issues.apache.org/jira/browse/CASSANDRA-2843?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sylvain Lebresne updated CASSANDRA-2843:
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Attachment: 2843_h.patch
bq. the IColumnMap name when it does not implement Map interface, and some
things it has in common with Map (iteration) it changes semantics of (iterating
values instead of keys). not sure what to use instead though, since we already
have an IColumnContainer. Maybe ISortedColumns?
Yeah, I'm not sure I have a better name either, maybe ISortedColumnHolder, but
not sure it's better than ISortedColumns so attached rebased patch simply
rename ColumnMap -> SortedColumns
bq. TSCM and ALCM extending instead of wrapping CSLM/AL, respectively
The idea was to save one object creation. I admit this is probably not a huge
deal, but it felt that in this case it was no big deal to extend instead of
wrapping either, so felt like worth "optimizing". I still stand by that choice
but I have no good argument against the criticism that it is possibly premature.
bq. unrelated reformatting
If we're talking about the ones in SuperColumn.java, sorry, I mistakenly forced
re-indentation on the file which rewrote the tab to spaces. New patch keeps the
old formatting. I'd mention that there is also a few places where I've rewrote
cf.getSortedColumns().iterator() to cf.iterator(), which is arguably a bit
gratuitous for this patch, but I figured this avoids creating a new Collection
in the case of CLSM and there's not so many occurrences.
> better performance on long row read
> -----------------------------------
>
> Key: CASSANDRA-2843
> URL: https://issues.apache.org/jira/browse/CASSANDRA-2843
> Project: Cassandra
> Issue Type: New Feature
> Reporter: Yang Yang
> Fix For: 1.0
>
> Attachments: 2843.patch, 2843_d.patch, 2843_g.patch, 2843_h.patch,
> fix.diff, microBenchmark.patch, patch_timing, std_timing
>
>
> currently if a row contains > 1000 columns, the run time becomes considerably
> slow (my test of
> a row with 30 00 columns (standard, regular) each with 8 bytes in name, and
> 40 bytes in value, is about 16ms.
> this is all running in memory, no disk read is involved.
> through debugging we can find
> most of this time is spent on
> [Wall Time] org.apache.cassandra.db.Table.getRow(QueryFilter)
> [Wall Time]
> org.apache.cassandra.db.ColumnFamilyStore.getColumnFamily(QueryFilter,
> ColumnFamily)
> [Wall Time]
> org.apache.cassandra.db.ColumnFamilyStore.getColumnFamily(QueryFilter, int,
> ColumnFamily)
> [Wall Time]
> org.apache.cassandra.db.ColumnFamilyStore.getTopLevelColumns(QueryFilter,
> int, ColumnFamily)
> [Wall Time]
> org.apache.cassandra.db.filter.QueryFilter.collectCollatedColumns(ColumnFamily,
> Iterator, int)
> [Wall Time]
> org.apache.cassandra.db.filter.SliceQueryFilter.collectReducedColumns(IColumnContainer,
> Iterator, int)
> [Wall Time] org.apache.cassandra.db.ColumnFamily.addColumn(IColumn)
> ColumnFamily.addColumn() is slow because it inserts into an internal
> concurrentSkipListMap() that maps column names to values.
> this structure is slow for two reasons: it needs to do synchronization; it
> needs to maintain a more complex structure of map.
> but if we look at the whole read path, thrift already defines the read output
> to be List<ColumnOrSuperColumn> so it does not make sense to use a luxury map
> data structure in the interium and finally convert it to a list. on the
> synchronization side, since the return CF is never going to be
> shared/modified by other threads, we know the access is always single thread,
> so no synchronization is needed.
> but these 2 features are indeed needed for ColumnFamily in other cases,
> particularly write. so we can provide a different ColumnFamily to
> CFS.getTopLevelColumnFamily(), so getTopLevelColumnFamily no longer always
> creates the standard ColumnFamily, but take a provided returnCF, whose cost
> is much cheaper.
> the provided patch is for demonstration now, will work further once we agree
> on the general direction.
> CFS, ColumnFamily, and Table are changed; a new FastColumnFamily is
> provided. the main work is to let the FastColumnFamily use an array for
> internal storage. at first I used binary search to insert new columns in
> addColumn(), but later I found that even this is not necessary, since all
> calling scenarios of ColumnFamily.addColumn() has an invariant that the
> inserted columns come in sorted order (I still have an issue to resolve
> descending or ascending now, but ascending works). so the current logic is
> simply to compare the new column against the end column in the array, if
> names not equal, append, if equal, reconcile.
> slight temporary hacks are made on getTopLevelColumnFamily so we have 2
> flavors of the method, one accepting a returnCF. but we could definitely
> think about what is the better way to provide this returnCF.
> this patch compiles fine, no tests are provided yet. but I tested it in my
> application, and the performance improvement is dramatic: it offers about 50%
> reduction in read time in the 3000-column case.
> thanks
> Yang
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