Can I propose an adjustment? If we add a timestamp to every table, we can generate the JSON on-the-fly. Then, the snapshot becomes a timestamp field, `snapshot_time`, and all the data `select` queries add `where timestamp <= snapshot_time limit 1`. Instead of updating rows, we only ever insert new rows with new timestamps. This gives us snapshots back to eternity, and if a snapshot ever breaks, rolling back is as simple as updating the `snapshot_time`. Our data is so tiny, space is almost certainly not a problem, but if it is, truncating is as easy as `delete where count > X and timestamp < Y`.
That gives us all the benefits of your plan, plus the benefits of relational data, type safety, more powerful querying, etc. And it shouldn't be much more work to implement: add timestamp columns, snapshotting updates the snapshot field, and getting the config simply runs what the snapshot otherwise would to create the JSON. If generation performance is an issue (it may be in Perl, probably not in Go), we can always cache the latest snapshot in memory, and only regenerate it when the `snapshot_time` changes. On Wed, Jul 26, 2017 at 9:08 AM, Gelinas, Derek <[email protected]> wrote: > That’s not a terrible idea. Fewer changes to the code that way for sure, > really just the DS interface page. > > > On Jul 26, 2017, at 10:30 AM, Nir Sopher <[email protected]> wrote: > > > > Hi Derek, > > > > As discussed in the summit, we also see significant value in > > > > 1. DS Deployment Granularity - using DS individual config files. > > 2. Delivery Service Configuration Versioning (DSCV) - separating the > > "provisioning" from the "deployment". > > 3. Improving the roll-out procedure, joining the capabilities #1 & #2 > > > > We are on the same page with these needs:) > > > > However, as I see it, these are #1 & #2 are 2 separate features, each has > > different requirements. > > For example, for DSCV, I would suggest to manage the versions as > standard > > rows in the Delivery-Service table, side by side with the "hot" DS > > configuration. > > This will allow the existing code (with minor adjustments) to properly > work > > on these rows. > > Furthermore, it also allows you to simply "restore" the DS "hot" > > configuration to a specified revision. > > It is also more resilient to DS table schema updates. > > > > I'll soon share, on another thread, a link to a "DSCV functional spec" I > > was working on. It extends the presentation > > <https://cwiki.apache.org/confluence/download/attachments/69407844/TC% > 20Summit%20-%20Spring%202017%20-%20Self-Service.pptx? > version=1&modificationDate=1495451091000&api=v2> > > we > > had in the summit. > > I would appreciate any inputs to this spec. > > > > Nir > > > > On Tue, Jul 25, 2017 at 10:13 PM, Gelinas, Derek < > [email protected]> > > wrote: > > > >> At the summit, there was some talk about changing the manner in which we > >> generate configuration files. The early stages of this idea had me > >> creating large CDN definition files, but in the course of our > discussion it > >> became clear that we would be better served by creating delivery service > >> configuration files instead. This would shift us from a > server-generated > >> implementation, as we have now, to generating the configuration files > for > >> the caches locally. The data for this would come from a new API that > would > >> provide the delivery service definitions in json format. > >> > >> What I’m envisioning is creating delivery service “snapshots” which are > >> saved to the database as json objects. These snapshots would have the > full > >> range of information specific to the delivery service, including the > new DS > >> profiles. The database would store up to five of these objects per DS, > and > >> one DS object would be set to “active” through the UI or API. > >> > >> In this way, we could create multiple versions of a delivery service, or > >> safely modify the definition currently “live” (but not necessarily > active) > >> in the database without changing the configuration in the field. > >> Configuration would only be changed when the DS was saved and then that > >> saved version was set to become active. In the reverse manner, existing > >> saved delivery services could be restored to the live DB for > modification. > >> > >> By divorcing the “live” db from the active configuration we prevent the > >> possibility of accidental edits affecting the field, or > edits-in-progress > >> from being sent out prematurely when one person is working on a delivery > >> service and another is queueing updates. > >> > >> Once set, it would be this active delivery service definition that would > >> be provided to the rest of traffic ops for any delivery service > >> operations. For config file generation, new API endpoints would be > created > >> that do the following: > >> > >> - List the delivery services and the active versions of each assigned to > >> the specific server. > >> - Provide the json object from the database when requested - I’m > thinking > >> that the endpoint would send the current active by default, or a > specific > >> version if specified. > >> > >> These definitions would be absurdly cacheable - we would not need to > worry > >> about sending stale data because each new version would have a > completely > >> different name - and so could be generated once and sent to thousands of > >> caches with greatly reduced load on traffic ops. The load would > consist of > >> the initial creation of the json object, and the minimal serving of that > >> object, so this would still result in greatly reduced load on the > traffic > >> ops host(s) even without the use of caching. Because of this, the new > >> cache management service could check with traffic ops multiple times per > >> minute for updates. Once a delivery service was changed, the new json > >> would be downloaded and configs generated on the cache itself. > >> > >> Other benefits of the use of a cache manager service rather than the ORT > >> script include: > >> > >> - Decreased load from logins - once the cache has logged in, it could > use > >> the cookie from the previous session and only re-login when that cookie > has > >> expired. we could also explore the use of certificates or keys instead, > >> and eliminate logins altogether. > >> - Multiple checks per minute rather than every X minutes - faster > checks, > >> more agile CDN. > >> - Service could provide regular status updates to traffic ops, giving us > >> the ability to keep an eye out for drastic shifts in i/o, unwanted > >> behavior, problems with the ATS service, etc. This leads to building a > >> traffic ops that can adapt itself on the fly to changing conditions and > >> adjust accordingly. > >> - Queue commands to run on the host from traffic ops. ATS restarts, > >> system reboots, all manner of things could be triggered and scheduled > right > >> from traffic ops. > >> > >> Thoughts? > >> > >> Derek > >
