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From "Fabien Rousseau (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-11349) MerkleTree mismatch when multiple range tombstones exists for the same partition and interval
Date Sun, 13 Mar 2016 11:51:36 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-11349?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Fabien Rousseau updated CASSANDRA-11349:
----------------------------------------
    Description: 
We observed that repair, for some of our clusters, streamed a lot of data and many partitions
were "out of sync".
Moreover, the read repair mismatch ratio is around 3% on those clusters, which is really high.

After investigation, it appears that, if two range tombstones exists for a partition for the
same range/interval, they're both included in the merkle tree computation.
But, if for some reason, on another node, the two range tombstones were already compacted
into a single range tombstone, this will result in a merkle tree difference.
Currently, this is clearly bad because MerkleTree differences are dependent on compactions
(and if a partition is deleted and created multiple times, the only way to ensure that repair
"works correctly"/"don't overstream data" is to major compact before each repair... which
is not really feasible).

Below is a list of steps allowing to easily reproduce this case:
{noformat}
ccm create test -v 2.1.13 -n 2 -s
ccm node1 cqlsh
CREATE KEYSPACE test_rt WITH replication = {'class': 'SimpleStrategy', 'replication_factor':
2};
USE test_rt;
CREATE TABLE IF NOT EXISTS table1 (
    c1 text,
    c2 text,
    c3 float,
    c4 float,
    PRIMARY KEY ((c1), c2)
);
INSERT INTO table1 (c1, c2, c3, c4) VALUES ( 'a', 'b', 1, 2);
DELETE FROM table1 WHERE c1 = 'a' AND c2 = 'b';
ctrl ^d
# now flush only one of the two nodes
ccm node1 flush 
ccm node1 cqlsh
USE test_rt;
INSERT INTO table1 (c1, c2, c3, c4) VALUES ( 'a', 'b', 1, 3);
DELETE FROM table1 WHERE c1 = 'a' AND c2 = 'b';
ctrl ^d
ccm node1 repair
# now grep the log and observe that there was some inconstencies detected between nodes (while
it shouldn't have detected any)
ccm node1 showlog | grep "out of sync"
{noformat}
Consequences of this are a costly repair, accumulating many small SSTables (up to thousands
for a rather short period of time when using VNodes, the time for compaction to absorb those
small files), but also an increased size on disk.


  was:
We observed that repair, for some of our clusters, streamed a lot of data and many partitions
were "out of sync".
Moreover, the read repair mismatch ratio is around 3% on those clusters, which is really high.

After investigation, it appears that, if two range tombstones exists for a partition for the
same range/interval, they're both included in the merkle tree computation.
But, if for some reason, on another node, the two range tombstones were already compacted
into a single range tombstone, this will result in a merkle tree difference.
Currently, this is clearly bad because MerkleTree differences are dependent on compactions
(and if a partition is deleted and created multiple times, the only way to ensure that repair
"works correctly"/"don't overstream data" is to major compact before each repair... which
is not really feasible).

Below is a list of steps allowing to easily reproduce this case:

ccm create test -v 2.1.13 -n 2 -s
ccm node1 cqlsh
CREATE KEYSPACE test_rt WITH replication = {'class': 'SimpleStrategy', 'replication_factor':
2};
USE test_rt;
CREATE TABLE IF NOT EXISTS table1 (
    c1 text,
    c2 text,
    c3 float,
    c4 float,
    PRIMARY KEY ((c1), c2)
);
INSERT INTO table1 (c1, c2, c3, c4) VALUES ( 'a', 'b', 1, 2);
DELETE FROM table1 WHERE c1 = 'a' AND c2 = 'b';
ctrl ^d
# now flush only one of the two nodes
ccm node1 flush 
ccm node1 cqlsh
USE test_rt;
INSERT INTO table1 (c1, c2, c3, c4) VALUES ( 'a', 'b', 1, 3);
DELETE FROM table1 WHERE c1 = 'a' AND c2 = 'b';
ctrl ^d
ccm node1 repair
# now grep the log and observe that there was some inconstencies detected between nodes (while
it shouldn't have detected any)
ccm node1 showlog | grep "out of sync"

Consequences of this are a costly repair, accumulating many small SSTables (up to thousands
for a rather short period of time when using VNodes, the time for compaction to absorb those
small files), but also an increased size on disk.



> MerkleTree mismatch when multiple range tombstones exists for the same partition and
interval
> ---------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-11349
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11349
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Fabien Rousseau
>
> We observed that repair, for some of our clusters, streamed a lot of data and many partitions
were "out of sync".
> Moreover, the read repair mismatch ratio is around 3% on those clusters, which is really
high.
> After investigation, it appears that, if two range tombstones exists for a partition
for the same range/interval, they're both included in the merkle tree computation.
> But, if for some reason, on another node, the two range tombstones were already compacted
into a single range tombstone, this will result in a merkle tree difference.
> Currently, this is clearly bad because MerkleTree differences are dependent on compactions
(and if a partition is deleted and created multiple times, the only way to ensure that repair
"works correctly"/"don't overstream data" is to major compact before each repair... which
is not really feasible).
> Below is a list of steps allowing to easily reproduce this case:
> {noformat}
> ccm create test -v 2.1.13 -n 2 -s
> ccm node1 cqlsh
> CREATE KEYSPACE test_rt WITH replication = {'class': 'SimpleStrategy', 'replication_factor':
2};
> USE test_rt;
> CREATE TABLE IF NOT EXISTS table1 (
>     c1 text,
>     c2 text,
>     c3 float,
>     c4 float,
>     PRIMARY KEY ((c1), c2)
> );
> INSERT INTO table1 (c1, c2, c3, c4) VALUES ( 'a', 'b', 1, 2);
> DELETE FROM table1 WHERE c1 = 'a' AND c2 = 'b';
> ctrl ^d
> # now flush only one of the two nodes
> ccm node1 flush 
> ccm node1 cqlsh
> USE test_rt;
> INSERT INTO table1 (c1, c2, c3, c4) VALUES ( 'a', 'b', 1, 3);
> DELETE FROM table1 WHERE c1 = 'a' AND c2 = 'b';
> ctrl ^d
> ccm node1 repair
> # now grep the log and observe that there was some inconstencies detected between nodes
(while it shouldn't have detected any)
> ccm node1 showlog | grep "out of sync"
> {noformat}
> Consequences of this are a costly repair, accumulating many small SSTables (up to thousands
for a rather short period of time when using VNodes, the time for compaction to absorb those
small files), but also an increased size on disk.



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