Re: [openstack-dev] [marconi] RabbitMQ (AMQP 0.9) driver for Marconi
Thanks Flavio, inline. On 6/13/14, 1:37 AM, "Flavio Percoco" wrote: >On 11/06/14 18:01 +, Janczuk, Tomasz wrote: >>Thanks Flavio, some comments inline below. >> >>On 6/11/14, 5:15 AM, "Flavio Percoco" wrote: >> 1. Marconi exposes HTTP APIs that allow messages to be listed without consuming them. This API cannot be implemented on top of AMQP 0.9 which implements a strict queueing semantics. >>> >>>I believe this is quite an important endpoint for Marconi. It's not >>>about listing messages but getting batch of messages. Wether it is >>>through claims or not doesn't really matter. What matters is giving >>>the user the opportunity to get a set of messages, do some work and >>>decide what to do with those messages afterwards. >> >>The sticky point here is that this Marconi¹s endpoint allows messages to >>be obtained *without* consuming them in the traditional messaging system >>sense: the messages remain visible to other consumers. It could be argued >>that such semantics can be implemented on top of AMQP by first getting >>the >>messages and then immediately releasing them for consumption by others, >>before the Marconi call returns. However, even that is only possible for >>messages that are at the front of the queue - the "paging" mechanism >>using >>markers cannot be supported. > >What matters is whether the listing functionality is useful or not. >Lets not think about it as "listing" or "paging" but about getting >batches of messages that are still available for others to process in >parallel. As mentioned in my previous email, AMQP has been a good way >to analyze the extra set of features Marconi exposes in the API but I >don't want to make the choice of usability based on whether >traditional messaging systems support it and how it could be >implemented there. This functionality is very useful in a number of scenarios. It has traditionally been the domain of database systems - flexible access to data is what DBs excel in (select top 1000 * from X order by create_date). Vast majority of existing messaging systems has a much more constrained and prescriptive way of accessing data than a database. Why does this functionality need to be part of Marconi? What are the benefits of listing messages in Marconi that cannot be realized with a plain database? In other words, if I need to access my data in that way, why would I use Marconi rather than a DB? > 5. Marconi message consumption API creates a ³claim ID² for a set of consumed messages, up to a limit. In the AMQP 0.9 model (as well as SQS and Azure Queues), ³claim ID² maps onto the concept of ³delivery tag² which has a 1-1 relationship with a message. Since there is no way to represent the 1-N mapping between claimID and messages in the AMQP 0.9 model, it effectively restrict consumption of messages to one per claimID. This in turn prevents batch consumption benefits. 6. Marconi message consumption acknowledgment requires both claimID and messageID to be provided. MessageID concept is missing in AMQP 0.9. In order to implement this API, assuming the artificial 1-1 restriction of claim-message mapping from #5 above, this API could be implemented by requiring that messageID === claimID. This is really a workaround. >>> >>>These 2 points represent quite a change in the way Marconi works and a >>>trade-off in terms of batch consumption (as you mentioned). I believe >>>we can have support for both things. For example, claimID+suffix where >>>suffix point to a specific claimed messages. >>> >>>I don't want to start an extended discussion about this here but lets >>>keep in mind that we may be able to support both. I personally think >>>Marconi's claim's are reasonable as they are, which means I currently >>>like them better than SQS's. >> >>What are the advantages of the Marconi model for claims over the SQS and >>Azure Queue model for acknowledgements? >> >>I think the SQS and Azure Queue model is both simpler and more flexible. >>But the key advantage is that it has been around for a while, has been >>proven to work, and people understand it. >> >>1. SQS and Azure require only one concept to acknowledge a message >>(receipt handle/pop receipt) as opposed to Marconi¹s two concepts >>(message >>ID + claim ID). SQS/Azure model is simpler. > >TBH, I'm not exactly sure where you're going with this. I mean, the >model may look simpler but it's not necessarily better nor easier to >implement. Keeping both, messages and claims, separate in terms of IDs >and management is flexible and powerful enough, IMHO. But I'm probably >missing your point. > >I don't believe requiring the messageID+ClaimID to delete a specific, >claimed, messages is hard. It may not be hard. It is just more complex than it needs to be to accomplish the same task. > >> >>2. Similarly to Marconi, SQS and Azure allow individual claimed messages >>to be deleted. This is a wash. > >Calling it a wash
Re: [openstack-dev] [marconi] RabbitMQ (AMQP 0.9) driver for Marconi
On 11/06/14 18:01 +, Janczuk, Tomasz wrote: Thanks Flavio, some comments inline below. On 6/11/14, 5:15 AM, "Flavio Percoco" wrote: 1. Marconi exposes HTTP APIs that allow messages to be listed without consuming them. This API cannot be implemented on top of AMQP 0.9 which implements a strict queueing semantics. I believe this is quite an important endpoint for Marconi. It's not about listing messages but getting batch of messages. Wether it is through claims or not doesn't really matter. What matters is giving the user the opportunity to get a set of messages, do some work and decide what to do with those messages afterwards. The sticky point here is that this Marconi¹s endpoint allows messages to be obtained *without* consuming them in the traditional messaging system sense: the messages remain visible to other consumers. It could be argued that such semantics can be implemented on top of AMQP by first getting the messages and then immediately releasing them for consumption by others, before the Marconi call returns. However, even that is only possible for messages that are at the front of the queue - the "paging" mechanism using markers cannot be supported. What matters is whether the listing functionality is useful or not. Lets not think about it as "listing" or "paging" but about getting batches of messages that are still available for others to process in parallel. As mentioned in my previous email, AMQP has been a good way to analyze the extra set of features Marconi exposes in the API but I don't want to make the choice of usability based on whether traditional messaging systems support it and how it could be implemented there. 5. Marconi message consumption API creates a ³claim ID² for a set of consumed messages, up to a limit. In the AMQP 0.9 model (as well as SQS and Azure Queues), ³claim ID² maps onto the concept of ³delivery tag² which has a 1-1 relationship with a message. Since there is no way to represent the 1-N mapping between claimID and messages in the AMQP 0.9 model, it effectively restrict consumption of messages to one per claimID. This in turn prevents batch consumption benefits. 6. Marconi message consumption acknowledgment requires both claimID and messageID to be provided. MessageID concept is missing in AMQP 0.9. In order to implement this API, assuming the artificial 1-1 restriction of claim-message mapping from #5 above, this API could be implemented by requiring that messageID === claimID. This is really a workaround. These 2 points represent quite a change in the way Marconi works and a trade-off in terms of batch consumption (as you mentioned). I believe we can have support for both things. For example, claimID+suffix where suffix point to a specific claimed messages. I don't want to start an extended discussion about this here but lets keep in mind that we may be able to support both. I personally think Marconi's claim's are reasonable as they are, which means I currently like them better than SQS's. What are the advantages of the Marconi model for claims over the SQS and Azure Queue model for acknowledgements? I think the SQS and Azure Queue model is both simpler and more flexible. But the key advantage is that it has been around for a while, has been proven to work, and people understand it. 1. SQS and Azure require only one concept to acknowledge a message (receipt handle/pop receipt) as opposed to Marconi¹s two concepts (message ID + claim ID). SQS/Azure model is simpler. TBH, I'm not exactly sure where you're going with this. I mean, the model may look simpler but it's not necessarily better nor easier to implement. Keeping both, messages and claims, separate in terms of IDs and management is flexible and powerful enough, IMHO. But I'm probably missing your point. I don't believe requiring the messageID+ClaimID to delete a specific, claimed, messages is hard. 2. Similarly to Marconi, SQS and Azure allow individual claimed messages to be deleted. This is a wash. Calling it a wash is neither helpful nor friendly. Why do you think it is a wash? Claiming a message does not delete the message, which means consumers may want to delete it before the claim is released. Do you have a better way to do it? 3. SQS and Azure allow a batch of messages *up to a particular receipt handle/pop receit* to be deleted. This is more flexible than Marconi¹s mechanism or deleting all messages associated with a particular claim, and works very well for the most common scenario of in-order message delivery. Pop semantic is on its way to the codebase. Limited claim deletes sounds like an interesting thing, lets talk about it. Want to submit a new spec? 7. RabbitMQ message acknowledgment MUST be sent over the same AMQP channel instance on which the message was originally received. This requires that the two Marconi HTTP calls that receive and acknowledge a message are affinitized to the same Marconi backend. It either substantially complicates
Re: [openstack-dev] [marconi] RabbitMQ (AMQP 0.9) driver for Marconi
Thanks Flavio, some comments inline below. On 6/11/14, 5:15 AM, "Flavio Percoco" wrote: >> >> 1. Marconi exposes HTTP APIs that allow messages to be listed without >>consuming them. This API cannot be implemented on top of AMQP 0.9 which >>implements a strict queueing semantics. > >I believe this is quite an important endpoint for Marconi. It's not >about listing messages but getting batch of messages. Wether it is >through claims or not doesn't really matter. What matters is giving >the user the opportunity to get a set of messages, do some work and >decide what to do with those messages afterwards. The sticky point here is that this Marconi¹s endpoint allows messages to be obtained *without* consuming them in the traditional messaging system sense: the messages remain visible to other consumers. It could be argued that such semantics can be implemented on top of AMQP by first getting the messages and then immediately releasing them for consumption by others, before the Marconi call returns. However, even that is only possible for messages that are at the front of the queue - the "paging" mechanism using markers cannot be supported. >> 3. Marconi exposes HTTP APIs that allow queues to be created, >>deleted, and listed. Queue creation and deletion can be implemented with >>AMQP 0.9, but listing queues is not possible with AMQP. However, listing >>queues can be implemented by accessing RabbitMQ management plugin over >>proprietary HTTP APIs that Rabbit exposes. > >We were really close to get rid of queues but we decided to keep them >around at the summit. One of the reasons to keep queues is their >metadata - rarely used but still useful for some use cases. > >Monitoring and UIs may be another interesting use case to keep queues >around as a first citizen resource. > >I must admit that keeping queues around still bugs me a bit but I'll >get over it. I suspect the metadata requirements will ultimately weigh a lot on this decision, and I understand Marconi so far did not really have a smoking gun case for queue metadata. In particular, if and when Marconi introduces an authentication/authorization model, the ACLs will need to be stored and managed somewhere. Queue metadata is a natural place to configure per-queue security. Both SQS and Azure Storage Queues model it that way. >> >> 5. Marconi message consumption API creates a ³claim ID² for a set of >>consumed messages, up to a limit. In the AMQP 0.9 model (as well as SQS >>and Azure Queues), ³claim ID² maps onto the concept of ³delivery tag² >>which has a 1-1 relationship with a message. Since there is no way to >>represent the 1-N mapping between claimID and messages in the AMQP 0.9 >>model, it effectively restrict consumption of messages to one per >>claimID. This in turn prevents batch consumption benefits. >> >> 6. Marconi message consumption acknowledgment requires both claimID >>and messageID to be provided. MessageID concept is missing in AMQP 0.9. >>In order to implement this API, assuming the artificial 1-1 restriction >>of claim-message mapping from #5 above, this API could be implemented by >>requiring that messageID === claimID. This is really a workaround. >> > >These 2 points represent quite a change in the way Marconi works and a >trade-off in terms of batch consumption (as you mentioned). I believe >we can have support for both things. For example, claimID+suffix where >suffix point to a specific claimed messages. > >I don't want to start an extended discussion about this here but lets >keep in mind that we may be able to support both. I personally think >Marconi's claim's are reasonable as they are, which means I currently >like them better than SQS's. What are the advantages of the Marconi model for claims over the SQS and Azure Queue model for acknowledgements? I think the SQS and Azure Queue model is both simpler and more flexible. But the key advantage is that it has been around for a while, has been proven to work, and people understand it. 1. SQS and Azure require only one concept to acknowledge a message (receipt handle/pop receipt) as opposed to Marconi¹s two concepts (message ID + claim ID). SQS/Azure model is simpler. 2. Similarly to Marconi, SQS and Azure allow individual claimed messages to be deleted. This is a wash. 3. SQS and Azure allow a batch of messages *up to a particular receipt handle/pop receit* to be deleted. This is more flexible than Marconi¹s mechanism or deleting all messages associated with a particular claim, and works very well for the most common scenario of in-order message delivery. > >> 7. RabbitMQ message acknowledgment MUST be sent over the same AMQP >>channel instance on which the message was originally received. This >>requires that the two Marconi HTTP calls that receive and acknowledge a >>message are affinitized to the same Marconi backend. It either >>substantially complicates driver implementation (server-side reverse >>proxing of requests) or adds new requirements onto the M
Re: [openstack-dev] [marconi] RabbitMQ (AMQP 0.9) driver for Marconi
On 10/06/14 18:12 +, Janczuk, Tomasz wrote: I the last few days I attempted to implement a RabbitMQ (AMQP 0.9) storage driver for Marconi. These are the take-aways from this experiment. High level, it showed that current Marconi APIs *cannot* be mapped onto the AMQP 0.9 abstractions. In fact, currently it is not even possible to support a subset of functionality that would allow both message publication and consumption. First and foremost, thank you! This is a great summary. I've been willing to do the same for quite some time and never got to it. Based on your findings, I'm making some questions that are not related to supporting AMQP drivers but having a better and reasonable API. 1. Marconi exposes HTTP APIs that allow messages to be listed without consuming them. This API cannot be implemented on top of AMQP 0.9 which implements a strict queueing semantics. I believe this is quite an important endpoint for Marconi. It's not about listing messages but getting batch of messages. Wether it is through claims or not doesn't really matter. What matters is giving the user the opportunity to get a set of messages, do some work and decide what to do with those messages afterwards. 2. Marconi exposes HTTP APIs that allow random access to messages by ID. This API cannot be implemented on top of AMQP 0.9 which does not allow random access to messages, and the message ID concept is not present in the model. We recently discussed the faith of this endpoint[0]. We can followup there or later on when we start discussing v2. 3. Marconi exposes HTTP APIs that allow queues to be created, deleted, and listed. Queue creation and deletion can be implemented with AMQP 0.9, but listing queues is not possible with AMQP. However, listing queues can be implemented by accessing RabbitMQ management plugin over proprietary HTTP APIs that Rabbit exposes. We were really close to get rid of queues but we decided to keep them around at the summit. One of the reasons to keep queues is their metadata - rarely used but still useful for some use cases. Monitoring and UIs may be another interesting use case to keep queues around as a first citizen resource. I must admit that keeping queues around still bugs me a bit but I'll get over it. 4. Marconi message publishing APIs return server-assigned message IDs. Message IDs are absent from the AMQP 0.9 model and so the result of message publication cannot provide them. I think this is related to whatever we decide for #2 5. Marconi message consumption API creates a “claim ID” for a set of consumed messages, up to a limit. In the AMQP 0.9 model (as well as SQS and Azure Queues), “claim ID” maps onto the concept of “delivery tag” which has a 1-1 relationship with a message. Since there is no way to represent the 1-N mapping between claimID and messages in the AMQP 0.9 model, it effectively restrict consumption of messages to one per claimID. This in turn prevents batch consumption benefits. 6. Marconi message consumption acknowledgment requires both claimID and messageID to be provided. MessageID concept is missing in AMQP 0.9. In order to implement this API, assuming the artificial 1-1 restriction of claim-message mapping from #5 above, this API could be implemented by requiring that messageID === claimID. This is really a workaround. These 2 points represent quite a change in the way Marconi works and a trade-off in terms of batch consumption (as you mentioned). I believe we can have support for both things. For example, claimID+suffix where suffix point to a specific claimed messages. I don't want to start an extended discussion about this here but lets keep in mind that we may be able to support both. I personally think Marconi's claim's are reasonable as they are, which means I currently like them better than SQS's. 7. RabbitMQ message acknowledgment MUST be sent over the same AMQP channel instance on which the message was originally received. This requires that the two Marconi HTTP calls that receive and acknowledge a message are affinitized to the same Marconi backend. It either substantially complicates driver implementation (server-side reverse proxing of requests) or adds new requirements onto the Marconi deployment (server affinity through load balancing). Nothing to do here. I guess a combination with a persistent-transport protocol would help but we don't want to make the store driver depend on the transport. 8. Currently Marconi does not support an HTTP API that allows a message to be consumed with immediate acknowledgement (such API is in the pipeline however). Despite the fact that such API would not even support the at-least-once guarantee, combined with the restriction from #7 it means that there is simply *no way* currently for a RabbitMQ based driver to implement any form of message consumption using today’s HTTP API. If Marconi aspires to support a range of implementation choice
[openstack-dev] [marconi] RabbitMQ (AMQP 0.9) driver for Marconi
I the last few days I attempted to implement a RabbitMQ (AMQP 0.9) storage driver for Marconi. These are the take-aways from this experiment. High level, it showed that current Marconi APIs *cannot* be mapped onto the AMQP 0.9 abstractions. In fact, currently it is not even possible to support a subset of functionality that would allow both message publication and consumption. 1. Marconi exposes HTTP APIs that allow messages to be listed without consuming them. This API cannot be implemented on top of AMQP 0.9 which implements a strict queueing semantics. 2. Marconi exposes HTTP APIs that allow random access to messages by ID. This API cannot be implemented on top of AMQP 0.9 which does not allow random access to messages, and the message ID concept is not present in the model. 3. Marconi exposes HTTP APIs that allow queues to be created, deleted, and listed. Queue creation and deletion can be implemented with AMQP 0.9, but listing queues is not possible with AMQP. However, listing queues can be implemented by accessing RabbitMQ management plugin over proprietary HTTP APIs that Rabbit exposes. 4. Marconi message publishing APIs return server-assigned message IDs. Message IDs are absent from the AMQP 0.9 model and so the result of message publication cannot provide them. 5. Marconi message consumption API creates a “claim ID” for a set of consumed messages, up to a limit. In the AMQP 0.9 model (as well as SQS and Azure Queues), “claim ID” maps onto the concept of “delivery tag” which has a 1-1 relationship with a message. Since there is no way to represent the 1-N mapping between claimID and messages in the AMQP 0.9 model, it effectively restrict consumption of messages to one per claimID. This in turn prevents batch consumption benefits. 6. Marconi message consumption acknowledgment requires both claimID and messageID to be provided. MessageID concept is missing in AMQP 0.9. In order to implement this API, assuming the artificial 1-1 restriction of claim-message mapping from #5 above, this API could be implemented by requiring that messageID === claimID. This is really a workaround. 7. RabbitMQ message acknowledgment MUST be sent over the same AMQP channel instance on which the message was originally received. This requires that the two Marconi HTTP calls that receive and acknowledge a message are affinitized to the same Marconi backend. It either substantially complicates driver implementation (server-side reverse proxing of requests) or adds new requirements onto the Marconi deployment (server affinity through load balancing). 8. Currently Marconi does not support an HTTP API that allows a message to be consumed with immediate acknowledgement (such API is in the pipeline however). Despite the fact that such API would not even support the at-least-once guarantee, combined with the restriction from #7 it means that there is simply *no way* currently for a RabbitMQ based driver to implement any form of message consumption using today’s HTTP API. If Marconi aspires to support a range of implementation choices for the HTTP APIs it prescribes, the HTTP APIs will likely need to be re-factored and simplified. Key issues are related to the APIs that allow messages to be looked up without consuming them, the explicit modeling of message IDs (unnecessary in systems with strict queuing semantics), and the acknowledgment (claim) model that is different from most acknowledgments models out there (SQS, Azure Queues, AMQP). I believe Marconi would benefit from a small set of core HTTP APIs that reflect a strict messaging semantics, providing a scenario parity with SQS or Azure Storage Queues. Thanks, Tomasz Janczuk @tjanczuk HP ___ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
