[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Sylvain Lebresne updated CASSANDRA-12126: - Source Control Link: [3.0|https://github.com/apache/cassandra/commit/2d0b16804785660e8515aca9944784fb3733c619], [3.11|https://github.com/apache/cassandra/commit/080280dc0177da6176dd4ba970e5a35aa7e2a729], [4.0|https://github.com/apache/cassandra/commit/9a3ca008bad2a7bfa887a] (was: [3.0|https://github.com/apache/cassandra/commit/2d0b16804785660e8515aca9944784fb3733c619],[3.11|https://github.com/apache/cassandra/commit/080280dc0177da6176dd4ba970e5a35aa7e2a729],[trunk|https://github.com/apache/cassandra/commit/9a3ca008bad2a7bfa887a]) > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Assignee: Sylvain Lebresne >Priority: Normal > Labels: LWT, pull-request-available > Fix For: 4.0-beta4, 3.0.24, 3.11.10 > > Time Spent: 10m > Remaining Estimate: 0h > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Sylvain Lebresne updated CASSANDRA-12126: - Source Control Link: [3.0|https://github.com/apache/cassandra/commit/2d0b16804785660e8515aca9944784fb3733c619],[3.11|https://github.com/apache/cassandra/commit/080280dc0177da6176dd4ba970e5a35aa7e2a729],[trunk|https://github.com/apache/cassandra/commit/9a3ca008bad2a7bfa887a] (was: [3.0|https://github.com/apache/cassandra/commit/2d0b16804785660e8515aca9944784fb3733c619], [3.11|https://github.com/apache/cassandra/commit/080280dc0177da6176dd4ba970e5a35aa7e2a729], [trunk|https://github.com/apache/cassandra/commit/9a3ca008bad2a7bfa887a) > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Assignee: Sylvain Lebresne >Priority: Normal > Labels: LWT, pull-request-available > Fix For: 4.0-beta4, 3.0.24, 3.11.10 > > Time Spent: 10m > Remaining Estimate: 0h > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Sylvain Lebresne updated CASSANDRA-12126: - Fix Version/s: (was: 4.0-beta) (was: 3.11.x) (was: 3.0.x) 3.11.10 3.0.24 4.0-beta4 Since Version: 2.0.0 Source Control Link: [3.0|https://github.com/apache/cassandra/commit/2d0b16804785660e8515aca9944784fb3733c619], [3.11|https://github.com/apache/cassandra/commit/080280dc0177da6176dd4ba970e5a35aa7e2a729], [trunk|https://github.com/apache/cassandra/commit/9a3ca008bad2a7bfa887a Resolution: Fixed Status: Resolved (was: Ready to Commit) Committed following the dev mailing list discussion. Thanks. > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Assignee: Sylvain Lebresne >Priority: Normal > Labels: LWT, pull-request-available > Fix For: 4.0-beta4, 3.0.24, 3.11.10 > > Time Spent: 10m > Remaining Estimate: 0h > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Benjamin Lerer updated CASSANDRA-12126: --- Status: Ready to Commit (was: Review In Progress) > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Assignee: Sylvain Lebresne >Priority: Normal > Labels: LWT, pull-request-available > Fix For: 3.0.x, 3.11.x, 4.0-beta > > Time Spent: 10m > Remaining Estimate: 0h > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Adam Holmberg updated CASSANDRA-12126: -- Complexity: Normal > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Assignee: Sylvain Lebresne >Priority: Normal > Labels: LWT, pull-request-available > Fix For: 3.0.x, 3.11.x, 4.0-beta > > Time Spent: 10m > Remaining Estimate: 0h > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Benjamin Lerer updated CASSANDRA-12126: --- Fix Version/s: (was: 4.0-triage) > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Assignee: Sylvain Lebresne >Priority: Normal > Labels: LWT, pull-request-available > Fix For: 3.0.x, 3.11.x, 4.0-beta > > Time Spent: 10m > Remaining Estimate: 0h > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Benjamin Lerer updated CASSANDRA-12126: --- Reviewers: Benjamin Lerer, Benjamin Lerer (was: Benjamin Lerer) Benjamin Lerer, Benjamin Lerer (was: Benjamin Lerer) Status: Review In Progress (was: Patch Available) > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Assignee: Sylvain Lebresne >Priority: Normal > Labels: LWT, pull-request-available > Fix For: 3.0.x, 3.11.x, 4.0-beta > > Time Spent: 10m > Remaining Estimate: 0h > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Benjamin Lerer updated CASSANDRA-12126: --- Fix Version/s: 4.0-rc 3.11.x 3.0.x > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Assignee: Sylvain Lebresne >Priority: Normal > Labels: LWT, pull-request-available > Fix For: 3.0.x, 3.11.x, 4.0-rc > > Time Spent: 10m > Remaining Estimate: 0h > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Benjamin Lerer updated CASSANDRA-12126: --- Fix Version/s: (was: 4.0-rc) 4.0-beta > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Assignee: Sylvain Lebresne >Priority: Normal > Labels: LWT, pull-request-available > Fix For: 3.0.x, 3.11.x, 4.0-beta > > Time Spent: 10m > Remaining Estimate: 0h > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Benjamin Lerer updated CASSANDRA-12126: --- Reviewers: Benjamin Lerer > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Assignee: Sylvain Lebresne >Priority: Normal > Labels: LWT, pull-request-available > Time Spent: 10m > Remaining Estimate: 0h > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Sylvain Lebresne updated CASSANDRA-12126: - Test and Documentation Plan: Included in-jvm dtests Status: Patch Available (was: Open) I'm only semi-sure how to parse Jenkins CI results these days but from what I can tell, all failures are unrelated so marking ready for review. > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Assignee: Sylvain Lebresne >Priority: Normal > Labels: LWT, pull-request-available > Time Spent: 10m > Remaining Estimate: 0h > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] ASF GitHub Bot updated CASSANDRA-12126: --- Labels: LWT pull-request-available (was: LWT) > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Priority: Normal > Labels: LWT, pull-request-available > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Benedict Elliott Smith updated CASSANDRA-12126: --- Component/s: Feature/Lightweight Transactions > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Feature/Lightweight Transactions, Legacy/Coordination >Reporter: Sankalp Kohli >Priority: Normal > Labels: LWT > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian Jira (v8.3.4#803005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Jeremy Hanna updated CASSANDRA-12126: - Labels: LWT (was: ) > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Coordination >Reporter: sankalp kohli >Priority: Major > Labels: LWT > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian JIRA (v7.6.3#76005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Stefan Podkowinski updated CASSANDRA-12126: --- Status: Open (was: Patch Available) > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Coordination >Reporter: sankalp kohli >Priority: Major > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian JIRA (v7.6.3#76005) - To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Stefan Podkowinski updated CASSANDRA-12126: --- Component/s: Coordination > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Coordination >Reporter: sankalp kohli >Assignee: Stefan Podkowinski > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian JIRA (v6.3.15#6346)
[jira] [Updated] (CASSANDRA-12126) CAS Reads Inconsistencies
[ https://issues.apache.org/jira/browse/CASSANDRA-12126?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Stefan Podkowinski updated CASSANDRA-12126: --- Status: Patch Available (was: In Progress) > CAS Reads Inconsistencies > -- > > Key: CASSANDRA-12126 > URL: https://issues.apache.org/jira/browse/CASSANDRA-12126 > Project: Cassandra > Issue Type: Bug > Components: Coordination >Reporter: sankalp kohli >Assignee: Stefan Podkowinski > > While looking at the CAS code in Cassandra, I found a potential issue with > CAS Reads. Here is how it can happen with RF=3 > 1) You issue a CAS Write and it fails in the propose phase. A machine replies > true to a propose and saves the commit in accepted filed. The other two > machines B and C does not get to the accept phase. > Current state is that machine A has this commit in paxos table as accepted > but not committed and B and C does not. > 2) Issue a CAS Read and it goes to only B and C. You wont be able to read the > value written in step 1. This step is as if nothing is inflight. > 3) Issue another CAS Read and it goes to A and B. Now we will discover that > there is something inflight from A and will propose and commit it with the > current ballot. Now we can read the value written in step 1 as part of this > CAS read. > If we skip step 3 and instead run step 4, we will never learn about value > written in step 1. > 4. Issue a CAS Write and it involves only B and C. This will succeed and > commit a different value than step 1. Step 1 value will never be seen again > and was never seen before. > If you read the Lamport “paxos made simple” paper and read section 2.3. It > talks about this issue which is how learners can find out if majority of the > acceptors have accepted the proposal. > In step 3, it is correct that we propose the value again since we dont know > if it was accepted by majority of acceptors. When we ask majority of > acceptors, and more than one acceptors but not majority has something in > flight, we have no way of knowing if it is accepted by majority of acceptors. > So this behavior is correct. > However we need to fix step 2, since it caused reads to not be linearizable > with respect to writes and other reads. In this case, we know that majority > of acceptors have no inflight commit which means we have majority that > nothing was accepted by majority. I think we should run a propose step here > with empty commit and that will cause write written in step 1 to not be > visible ever after. > With this fix, we will either see data written in step 1 on next serial read > or will never see it which is what we want. -- This message was sent by Atlassian JIRA (v6.3.15#6346)
