Re: expiring + counter column?
The comment around line 448 in StorageProxy
// We do the replication on another stage because it
involves a read (see CM.makeReplicationMutation)
// and we want to avoid blocking too much the MUTATION stage
The read happens on another stage, it is not part of the mutation.
And the test before that checks shouldReplicateOnWrite for the CF's involved in
the mutation, which defaults to false.
See also the comments for StorageProxy.mutateCounter() and this comment which I
*think* is still valid
https://issues.apache.org/jira/browse/CASSANDRA-1909?focusedCommentId=12976727&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-12976727
Cheers
-
Aaron Morton
Freelance Cassandra Developer
@aaronmorton
http://www.thelastpickle.com
On 30 May 2011, at 06:41, Yang wrote:
> yeah, then maybe we can make that a silent omission. less desirable, but
> still better than unpredicted behavior. (this is not that bad: currently you
> can't know whether a write result really reached a quorum, i.e. become
> "effective", anyway)
>
>
> regarding "we never look at SStables", I think right now counter adds do
> require a read on SStables, although asynchronously:
> StorageProxy:
> private static void applyCounterMutation(final IMutation mutation, final
> Multimap hintedEndpoints, final
> IWriteResponseHandler responseHandler, final String localDataCenter, final
> ConsistencyLevel consistency_level, boolean executeOnMutationStage) {
> ..
>
> sendToHintedEndpoints(cm.makeReplicationMutation(), hintedEndpoints,
> responseHandler, localDataCenter, false, consistency_level);
>
> }
>
>
> CounterMutation.java:
> public RowMutation makeReplicationMutation() throws IOException {
>
>
> Table table = Table.open(readCommand.table);
> Row row = readCommand.getRow(table);
>
> }
>
>
> I think the "getRow()" line above does what the .pdf design doc in the JIRA
> described: replication to other replicas (non-leaders) replicate only the
> **sum** that I own, not individual delta that I just received. actually I'm
> not quite understanding why this approach was chosen, since it makes each
> write into read---write (when getReplicateOnWrite() ) , which can be slow.
> I'm still trying to understand that
>
>
> Thanks
> Yang
>
> On Sun, May 29, 2011 at 3:45 AM, aaron morton wrote:
> Without commenting on the other parts of the design, this part is not
> possible "attempts to add to a dead counter throws an exception "
>
> All write operations are no look operations (write to the log, update
> memtables) we never look at the SSTables. It goes against the architecture of
> the write path to require a read from disk.
>
> Cheers
>
> -
> Aaron Morton
> Freelance Cassandra Developer
> @aaronmorton
> http://www.thelastpickle.com
>
> On 29 May 2011, at 20:04, Yang wrote:
>
>>
>> sorry in the notation, instead of "ttl" I mean "timestamp"
>>
>>
>> On Sun, May 29, 2011 at 12:24 AM, Yang wrote:
>> sorry to beat on the dead horse.
>>
>> I looked at the link referred from #2103 :
>> https://issues.apache.org/jira/browse/CASSANDRA-2101
>> I agree with the reasoning in #2101 that the ultimate issue is that delete
>> and counter adds are not commutative. since by definition we can't achieve
>> predictable behavior with deletes + counter, can we redefine the behavior of
>> counter deletes, so that we can always guarantee the declared behavior? ---
>> specifically:
>>
>>
>> we define that once a counter column is deleted, you can never add to it
>> again. attempts to add to a dead counter throws an exception all
>> future adds are just ignored. i.e. a counter column has only one life,
>> until all tombstones are purged from system, after which it is possible for
>> the counter to have a new incarnation. basically instead of solving the
>> problem raised in #2103, we declare openly that it's unsolvable (which is
>> true), and make the code reflect this fact.
>>
>>
>>
>> I think this behavior would satisfy most use cases of counters. so instead
>> of relying on the advice to developers: "do not do updates for a period
>> after deletes, otherwise it probably wont' work", we enforce this into the
>> code.
>>
>>
>> the same logic can be carried over into expiring column, since they are
>> essentially automatically inserted deletes. that way #2103 could be "solved"
>>
>>
>> I'm attaching an example below, you can refer to them if needed.
>>
>> Thanks a lot
>> Yang
>>
>>
>> example:
>> for simplicity we assume there is only one column family , one column, so we
>> omit column name and cf name in our notation, assume all counterColumns have
>> a delta value of 1, we only mark their ttl now. so c(123) means a counter
>> column of ttl=1, adding a delta of 1. d(456) means a tombstone with
Re: expiring + counter column?
yeah, then maybe we can make that a silent omission. less desirable, but
still better than unpredicted behavior. (this is not that bad: currently you
can't know whether a write result really reached a quorum, i.e. become
"effective", anyway)
regarding "we never look at SStables", I think right now counter adds do
require a read on SStables, although asynchronously:
StorageProxy:
private static void applyCounterMutation(final IMutation mutation, final
Multimap hintedEndpoints, final
IWriteResponseHandler responseHandler, final String localDataCenter, final
ConsistencyLevel consistency_level, boolean executeOnMutationStage) {
..
sendToHintedEndpoints(cm.makeReplicationMutation(), hintedEndpoints,
responseHandler, localDataCenter, false, consistency_level);
}
CounterMutation.java:
public RowMutation makeReplicationMutation() throws IOException {
Table table = Table.open(readCommand.table);
Row row = readCommand.getRow(table);
}
I think the "getRow()" line above does what the .pdf design doc in the JIRA
described: replication to other replicas (non-leaders) replicate only the
**sum** that I own, not individual delta that I just received. actually I'm
not quite understanding why this approach was chosen, since it makes each
write into read---write (when getReplicateOnWrite() ) , which can be slow.
I'm still trying to understand that
Thanks
Yang
On Sun, May 29, 2011 at 3:45 AM, aaron morton wrote:
> Without commenting on the other parts of the design, this part is not
> possible "attempts to add to a dead counter throws an exception "
>
> All write operations are no look operations (write to the log, update
> memtables) we never look at the SSTables. It goes against the architecture
> of the write path to require a read from disk.
>
> Cheers
>
> -
> Aaron Morton
> Freelance Cassandra Developer
> @aaronmorton
> http://www.thelastpickle.com
>
> On 29 May 2011, at 20:04, Yang wrote:
>
>
> sorry in the notation, instead of "ttl" I mean "timestamp"
>
>
> On Sun, May 29, 2011 at 12:24 AM, Yang wrote:
>
>> sorry to beat on the dead horse.
>>
>> I looked at the link referred from #2103 :
>> https://issues.apache.org/jira/browse/CASSANDRA-2101
>> I agree with the reasoning in #2101 that the ultimate issue is that delete
>> and counter adds are not commutative. since by definition we can't achieve
>> predictable behavior with deletes + counter, can we redefine the behavior
>> of counter deletes, so that we can always guarantee the declared behavior?
>> --- specifically:
>>
>>
>> *we define that once a counter column is deleted, you can never add to it
>> again.* attempts to add to a dead counter throws an exception all
>> future adds are just ignored. i.e. a counter column has only one life,
>> until all tombstones are purged from system, after which it is possible for
>> the counter to have a new incarnation. basically instead of solving the
>> problem raised in #2103, we declare openly that it's unsolvable (which is
>> true), and make the code reflect this fact.
>>
>>
>>
>> I think this behavior would satisfy most use cases of counters. so instead
>> of relying on the advice to developers: "do not do updates for a period
>> after deletes, otherwise it probably wont' work", we enforce this into the
>> code.
>>
>>
>> the same logic can be carried over into expiring column, since they are
>> essentially automatically inserted deletes. that way #2103 could be "solved"
>>
>>
>> I'm attaching an example below, you can refer to them if needed.
>>
>> Thanks a lot
>> Yang
>>
>>
>> example:
>> for simplicity we assume there is only one column family , one column, so
>> we omit column name and cf name in our notation, assume all counterColumns
>> have a delta value of 1, we only mark their ttl now. so c(123) means a
>> counter column of ttl=1, adding a delta of 1. d(456) means a tombstone with
>> ttl=456.
>>
>> then we can have the following operations
>>
>> operationresult after operation
>> --
>> c(1)count=1
>> d(2)count = null ( counter not present )
>>
>> c(3)count = null ( add on dead counter
>> ignored)
>> ---
>>
>>
>> if the 2 adds arrive out of order , we would still guarantee eventual
>> consistency:
>>
>> operationresult after operation
>>
>>
>> c(1)count=1
>> c(3)count=2 (we have 2 adds, each with
>> delta=1)
>> d(2)count=null (deleted)
>> --
>> at the end of both scenarios, the result is guaranteed to be null;
>> note that in the second scenar
Re: expiring + counter column?
Without commenting on the other parts of the design, this part is not possible "attempts to add to a dead counter throws an exception " All write operations are no look operations (write to the log, update memtables) we never look at the SSTables. It goes against the architecture of the write path to require a read from disk. Cheers - Aaron Morton Freelance Cassandra Developer @aaronmorton http://www.thelastpickle.com On 29 May 2011, at 20:04, Yang wrote: > > sorry in the notation, instead of "ttl" I mean "timestamp" > > > On Sun, May 29, 2011 at 12:24 AM, Yang wrote: > sorry to beat on the dead horse. > > I looked at the link referred from #2103 : > https://issues.apache.org/jira/browse/CASSANDRA-2101 > I agree with the reasoning in #2101 that the ultimate issue is that delete > and counter adds are not commutative. since by definition we can't achieve > predictable behavior with deletes + counter, can we redefine the behavior of > counter deletes, so that we can always guarantee the declared behavior? --- > specifically: > > > we define that once a counter column is deleted, you can never add to it > again. attempts to add to a dead counter throws an exception all > future adds are just ignored. i.e. a counter column has only one life, until > all tombstones are purged from system, after which it is possible for the > counter to have a new incarnation. basically instead of solving the problem > raised in #2103, we declare openly that it's unsolvable (which is true), and > make the code reflect this fact. > > > > I think this behavior would satisfy most use cases of counters. so instead of > relying on the advice to developers: "do not do updates for a period after > deletes, otherwise it probably wont' work", we enforce this into the code. > > > the same logic can be carried over into expiring column, since they are > essentially automatically inserted deletes. that way #2103 could be "solved" > > > I'm attaching an example below, you can refer to them if needed. > > Thanks a lot > Yang > > > example: > for simplicity we assume there is only one column family , one column, so we > omit column name and cf name in our notation, assume all counterColumns have > a delta value of 1, we only mark their ttl now. so c(123) means a counter > column of ttl=1, adding a delta of 1. d(456) means a tombstone with ttl=456. > > then we can have the following operations > > operationresult after operation > -- > c(1)count=1 > d(2)count = null ( counter not present ) > > c(3)count = null ( add on dead counter ignored) > --- > > > if the 2 adds arrive out of order , we would still guarantee eventual > consistency: > > operationresult after operation > > c(1)count=1 > c(3)count=2 (we have 2 adds, each with delta=1) > d(2)count=null (deleted) > -- > at the end of both scenarios, the result is guaranteed to be null; > note that in the second scenario, line 2 shows a snapshot where we have a > state with count=2, which scenario 1 never sees this. this is fine, since > even regular columns can have this situation (just consider if the counter > columns were inserts/overwrites instead ) > > > > On Fri, May 27, 2011 at 5:57 PM, Jonathan Ellis wrote: > > No. See comments to https://issues.apache.org/jira/browse/CASSANDRA-2103 > > > > On Fri, May 27, 2011 at 7:29 PM, Yang wrote: > >> is this combination feature available , or on track ? > >> > >> thanks > >> Yang > >> > > > > > > > > -- > > Jonathan Ellis > > Project Chair, Apache Cassandra > > co-founder of DataStax, the source for professional Cassandra support > > http://www.datastax.com > > > >
Re: expiring + counter column?
sorry in the notation, instead of "ttl" I mean "timestamp" On Sun, May 29, 2011 at 12:24 AM, Yang wrote: > sorry to beat on the dead horse. > > I looked at the link referred from #2103 : > https://issues.apache.org/jira/browse/CASSANDRA-2101 > I agree with the reasoning in #2101 that the ultimate issue is that delete > and counter adds are not commutative. since by definition we can't achieve > predictable behavior with deletes + counter, can we redefine the behavior > of counter deletes, so that we can always guarantee the declared behavior? > --- specifically: > > > *we define that once a counter column is deleted, you can never add to it > again.* attempts to add to a dead counter throws an exception all > future adds are just ignored. i.e. a counter column has only one life, > until all tombstones are purged from system, after which it is possible for > the counter to have a new incarnation. basically instead of solving the > problem raised in #2103, we declare openly that it's unsolvable (which is > true), and make the code reflect this fact. > > > > I think this behavior would satisfy most use cases of counters. so instead > of relying on the advice to developers: "do not do updates for a period > after deletes, otherwise it probably wont' work", we enforce this into the > code. > > > the same logic can be carried over into expiring column, since they are > essentially automatically inserted deletes. that way #2103 could be "solved" > > > I'm attaching an example below, you can refer to them if needed. > > Thanks a lot > Yang > > > example: > for simplicity we assume there is only one column family , one column, so > we omit column name and cf name in our notation, assume all counterColumns > have a delta value of 1, we only mark their ttl now. so c(123) means a > counter column of ttl=1, adding a delta of 1. d(456) means a tombstone with > ttl=456. > > then we can have the following operations > > operationresult after operation > -- > c(1)count=1 > d(2)count = null ( counter not present ) > > c(3)count = null ( add on dead counter ignored) > --- > > > if the 2 adds arrive out of order , we would still guarantee eventual > consistency: > > operationresult after operation > > > c(1)count=1 > c(3)count=2 (we have 2 adds, each with > delta=1) > d(2)count=null (deleted) > -- > at the end of both scenarios, the result is guaranteed to be null; > note that in the second scenario, line 2 shows a snapshot where we have a > state with count=2, which scenario 1 never sees this. this is fine, since > even regular columns can have this situation (just consider if the counter > columns were inserts/overwrites instead ) > > > > On Fri, May 27, 2011 at 5:57 PM, Jonathan Ellis wrote: > > No. See comments to https://issues.apache.org/jira/browse/CASSANDRA-2103 > > > > On Fri, May 27, 2011 at 7:29 PM, Yang wrote: > >> is this combination feature available , or on track ? > >> > >> thanks > >> Yang > >> > > > > > > > > -- > > Jonathan Ellis > > Project Chair, Apache Cassandra > > co-founder of DataStax, the source for professional Cassandra support > > http://www.datastax.com > > > >
Re: expiring + counter column?
errata: "so c(123) means a counter column of ttl=1," > "so c(123) means a counter column of ttl=123," On Sun, May 29, 2011 at 12:24 AM, Yang wrote: > sorry to beat on the dead horse. > > I looked at the link referred from #2103 : > https://issues.apache.org/jira/browse/CASSANDRA-2101 > I agree with the reasoning in #2101 that the ultimate issue is that delete > and counter adds are not commutative. since by definition we can't achieve > predictable behavior with deletes + counter, can we redefine the behavior > of counter deletes, so that we can always guarantee the declared behavior? > --- specifically: > > > *we define that once a counter column is deleted, you can never add to it > again.* attempts to add to a dead counter throws an exception all > future adds are just ignored. i.e. a counter column has only one life, > until all tombstones are purged from system, after which it is possible for > the counter to have a new incarnation. basically instead of solving the > problem raised in #2103, we declare openly that it's unsolvable (which is > true), and make the code reflect this fact. > > > > I think this behavior would satisfy most use cases of counters. so instead > of relying on the advice to developers: "do not do updates for a period > after deletes, otherwise it probably wont' work", we enforce this into the > code. > > > the same logic can be carried over into expiring column, since they are > essentially automatically inserted deletes. that way #2103 could be "solved" > > > I'm attaching an example below, you can refer to them if needed. > > Thanks a lot > Yang > > > example: > for simplicity we assume there is only one column family , one column, so > we omit column name and cf name in our notation, assume all counterColumns > have a delta value of 1, we only mark their ttl now. so c(123) means a > counter column of ttl=1, adding a delta of 1. d(456) means a tombstone with > ttl=456. > > then we can have the following operations > > operationresult after operation > -- > c(1)count=1 > d(2)count = null ( counter not present ) > > c(3)count = null ( add on dead counter ignored) > --- > > > if the 2 adds arrive out of order , we would still guarantee eventual > consistency: > > operationresult after operation > > > c(1)count=1 > c(3)count=2 (we have 2 adds, each with > delta=1) > d(2)count=null (deleted) > -- > at the end of both scenarios, the result is guaranteed to be null; > note that in the second scenario, line 2 shows a snapshot where we have a > state with count=2, which scenario 1 never sees this. this is fine, since > even regular columns can have this situation (just consider if the counter > columns were inserts/overwrites instead ) > > > > On Fri, May 27, 2011 at 5:57 PM, Jonathan Ellis wrote: > > No. See comments to https://issues.apache.org/jira/browse/CASSANDRA-2103 > > > > On Fri, May 27, 2011 at 7:29 PM, Yang wrote: > >> is this combination feature available , or on track ? > >> > >> thanks > >> Yang > >> > > > > > > > > -- > > Jonathan Ellis > > Project Chair, Apache Cassandra > > co-founder of DataStax, the source for professional Cassandra support > > http://www.datastax.com > > > >
Re: expiring + counter column?
sorry to beat on the dead horse. I looked at the link referred from #2103 : https://issues.apache.org/jira/browse/CASSANDRA-2101 I agree with the reasoning in #2101 that the ultimate issue is that delete and counter adds are not commutative. since by definition we can't achieve predictable behavior with deletes + counter, can we redefine the behavior of counter deletes, so that we can always guarantee the declared behavior? --- specifically: *we define that once a counter column is deleted, you can never add to it again.* attempts to add to a dead counter throws an exception all future adds are just ignored. i.e. a counter column has only one life, until all tombstones are purged from system, after which it is possible for the counter to have a new incarnation. basically instead of solving the problem raised in #2103, we declare openly that it's unsolvable (which is true), and make the code reflect this fact. I think this behavior would satisfy most use cases of counters. so instead of relying on the advice to developers: "do not do updates for a period after deletes, otherwise it probably wont' work", we enforce this into the code. the same logic can be carried over into expiring column, since they are essentially automatically inserted deletes. that way #2103 could be "solved" I'm attaching an example below, you can refer to them if needed. Thanks a lot Yang example: for simplicity we assume there is only one column family , one column, so we omit column name and cf name in our notation, assume all counterColumns have a delta value of 1, we only mark their ttl now. so c(123) means a counter column of ttl=1, adding a delta of 1. d(456) means a tombstone with ttl=456. then we can have the following operations operationresult after operation -- c(1)count=1 d(2)count = null ( counter not present ) c(3)count = null ( add on dead counter ignored) --- if the 2 adds arrive out of order , we would still guarantee eventual consistency: operationresult after operation c(1)count=1 c(3)count=2 (we have 2 adds, each with delta=1) d(2)count=null (deleted) -- at the end of both scenarios, the result is guaranteed to be null; note that in the second scenario, line 2 shows a snapshot where we have a state with count=2, which scenario 1 never sees this. this is fine, since even regular columns can have this situation (just consider if the counter columns were inserts/overwrites instead ) On Fri, May 27, 2011 at 5:57 PM, Jonathan Ellis wrote: > No. See comments to https://issues.apache.org/jira/browse/CASSANDRA-2103 > > On Fri, May 27, 2011 at 7:29 PM, Yang wrote: >> is this combination feature available , or on track ? >> >> thanks >> Yang >> > > > > -- > Jonathan Ellis > Project Chair, Apache Cassandra > co-founder of DataStax, the source for professional Cassandra support > http://www.datastax.com >
Re: expiring + counter column?
How about implementing a freezing mechanism on counter columns. If there are no more increments within "freeze" seconds after the last increments (it would be orders or day or so); the column would lock itself on increments and won't accept increment. And after this freeze perioid, the ttl should work fine. The column will be gone forever after freeze + ttl seconds. On Sat, May 28, 2011 at 2:57 AM, Jonathan Ellis wrote: > No. See comments to https://issues.apache.org/jira/browse/CASSANDRA-2103 > > On Fri, May 27, 2011 at 7:29 PM, Yang wrote: > > is this combination feature available , or on track ? > > > > thanks > > Yang > > > > > > -- > Jonathan Ellis > Project Chair, Apache Cassandra > co-founder of DataStax, the source for professional Cassandra support > http://www.datastax.com >
Re: expiring + counter column?
No. See comments to https://issues.apache.org/jira/browse/CASSANDRA-2103 On Fri, May 27, 2011 at 7:29 PM, Yang wrote: > is this combination feature available , or on track ? > > thanks > Yang > -- Jonathan Ellis Project Chair, Apache Cassandra co-founder of DataStax, the source for professional Cassandra support http://www.datastax.com
