Re: duplicated hbase timestamps

Sun, 14 Dec 2008 14:42:03 -0800

The below looks like the known issue, HBASE-29 'HStore#get and HStore#getFull may not return expected values by timestamp when there is more than one MapFile'. What do you think Toby? Basically, if updates do not go in in chronological order, you'll get unexpected results. We need to fix this but first need to get ourselves set up with some smarter internals before we can address it (Though, that said, I'd think your particular case shouldn't be that hard to make work). 

St.Ack

Toby White wrote:
Sorry for the very slow response - local priorities changed and I didn't have a chance to respond properly before.
The issue described previously is still occurring (brief recap - hbase is reporting cells with duplicate timestamps, see the quoted output below.)
I originally saw this with 0.18.0 - I've now checked, and I still see it with 0.18.1 (both on hadoop 0.18.1) and current trunk:r725828 (with hdfs upgraded to run on hadoop 0.19.0) 

This is running in pseudo-distributed mode.
I've been able to narrow down the trigger a bit. I can't cause it to happen entirely reproducibly, but it seems 
to occur only when I've done the following:

* Create a row;
* Add lots of data at different timestamps into one column (thrift mutateRowTs or shell put) * Delete all data in that column, or indeed the entire row (thrift deleteAll or deleteAllRow or shell deleteall) 
* at this point, hbase reports that the row has indeed been removed.
* Recreate the row, and put data back into the same column, at the same timestamps, but with potentially different values (thrift mutateRowTs / shell put) * On reading the row, Hbase seems to see and report back both the newly-added data, and the data previously deleted (thrift getVer / shell get)
On a row where this has happened once, it seems to happen almost always thereafter, each time appending a whole new set of data. So, if you're adding/removing 100 cells at a time, then the total number of cells hbase reports back will grow by 100 every time you repeat the cycle.
On a row where it hasn't happened yet, the delete behaviour seems usually correct.
The problem is observable working either through the Python thrift interface, or directly through the Hbase JRuby shell.
The HDFS filesystem on which I'm observing this is fairly small - under 100Mb compressed - I can forward it for debugging off list if that's helpful. I'd be grateful for any help sorting this out. 

Toby

On 20 Oct 2008, at 17:51, Jean-Daniel Cryans wrote:


Toby,

Can you tell us more about your setup? Numbers of machines, if NTP is
installed and running, number of regions in your table and other useful
stuff.

Thx,

J-D

On Mon, Oct 20, 2008 at 11:11 AM, Toby White
<[email protected]>wrote:
I'm seeing a strange effect on my hbase instance. Sometimes, on requesting 
the full history of a column, I get back individual cells several times
over.

That is, I'm getting results like this:

base(main):006:0* get 'my_table', 'scw9npU7Q4ma_khXqlDGXg', {COLUMN =>
'value:', VERSIONS=>4000}
timestamp=1224504133000, value=1013.0
timestamp=1224502749000, value=1012.0
timestamp=1224502749000, value=1012.0
timestamp=1224499880000, value=1011.0
timestamp=1224499880000, value=1011.0
timestamp=1224499880000, value=1011.0
timestamp=1224415961000, value=1010.0
timestamp=1224415961000, value=1010.0
timestamp=1224415961000, value=1010.0
timestamp=1224415701000, value=1009.0
timestamp=1224415701000, value=1009.0
timestamp=1224415701000, value=1009.0
timestamp=1224414200000, value=1008.0
timestamp=1224414200000, value=1008.0
timestamp=1224414200000, value=1008.0

This happens both through the hbase shell as shown here, and when
communicating with the server via thrift.
In either case, the cells are reported either as shown above; that is, with each cell simply repeated several times (in this case, 3) or sometimes with 
the series repeated; something like this:
base(main):006:0* get 'golddigger', 'scw9npU7Q4ma_khXqlDGXg', {COLUMN => 
'value:', VERSIONS=>4000}
timestamp=1224504133000, value=1013.0
timestamp=1224502749000, value=1012.0
timestamp=1224499880000, value=1011.0
timestamp=1224415961000, value=1010.0
timestamp=1224415701000, value=1009.0
timestamp=1224414200000, value=1008.0
timestamp=1224504133000, value=1013.0
timestamp=1224502749000, value=1012.0
timestamp=1224499880000, value=1011.0
timestamp=1224415961000, value=1010.0
timestamp=1224415701000, value=1009.0
timestamp=1224414200000, value=1008.0
or sometimes a combination of both ie an entire series, each cell repeated 
a couple of times, and then the whole lot repeated again.
This doesn't happen with all rows, only some of them, apparently at random. Sometimes, restarting hbase & the underlying hdf makes the problem go away; 
sometimes, it doesn't, and the issue persists.

This is with hbase 0.18.0 on hadoop 0.18.1

Is this a known issue?

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