This approach prevents concurrent data changes and ensures subsequent reads of the table see a stable view of committed data. To achieve this, you can obtain SHARE lock mode over the table before querying. For example, suppose an application runs a transaction at the isolation level read committed and needs to ensure that data in a table remains stable for the rest of the transaction. LOCK TABLE provides for cases when you might need more restrictive locking. When acquiring locks for commands that reference tables, EDB Postgres Advanced Server always uses the least restrictive lock mode possible. There's no UNLOCK TABLE command locks are always released at transaction end. Once obtained, the lock is held for the remainder of the current transaction. If the lock can't be acquired immediately, the command is aborted and an error occurs. If you specify NOWAIT, LOCK TABLE doesn't wait to acquire the desired lock. LOCK TABLE obtains a table-level lock, waiting if necessary for any conflicting locks to be released. Resource group would be beneficial for eliminating potential risks and answering customer’s questions.Toggle Wrap Copy ROW SHARE | ROW EXCLUSIVE | SHARE | SHARE ROW EXCLUSIVE | EXCLUSIVE Description An investigation of comparing resource queue/ I talked Wu just now and summarized our discussion as above. Performance to resource queue at all scenarios? In fact, CATL has raised the concerns when they were suggested to move to resource group. Group able to match all requirements based on resource queue when customer move to resource group? What is about the impact to existing application-level architecture and how much effort is expected? Does resource group have better than, or at least the same L Resource group’s capability for resource queue (functionality and performance). The result is customer will have no option and HAVE TO move to resource group when upgrading to GP7. To resolve the problem thoroughly, we must remove theĬode rather than just deprecating the functionality. As Deep figured out, one of major reasons to remove it is code invasion to Postgres lock mechanism. It in code as long as possible for compatibility of old versions. In general, we deprecate a functionality but keep L The concrete time to remove resource queue. However, I also have some concerns about: Partition lock), it is possible to cause subtle invalid lock protection due to other code defects, which is very hard to be tracked, as the issue we hit from CATL jira. I totally agree to remove resource queue in technique perspective.īesides the reasons mentioned by Deep, I’d like to supplement a reason: because of the implementation of resource requeue (calculating hash code on members but memory address of Add appropriate deprecation notices to GP6. This means ripping out any changes made to accommodate resource queues.ģ. Completely align Postgres based locking code with upstream Postgres lockingĬode. Delete all resource queue code, documentation and other artifacts from GP7.Ģ. Large turnaround time to support/maintain this feature fixes.ġ. Iv) There is little in-code documentation on any of the aforementionedģ. To lock data structures such as PROCLOCK for instance. To Postgres locking code to accommodate resourcequeues. Iii) Though much much smaller in relative footprint, subtle changes are present These are missing from the resource queue lock routines. Infrastructure changes that brought performance improvements as well asĬritical fixes. With the Postgres merges 9.6-12, we saw a lot of locking Inception while the upstream routines have improved, absorbed critical fixes There are undocumented subtleĭiffs that are there from inception. So there is a ResLock* functionĮach routine varies in subtle and dangerous ways. Ii) But to manipulate resource queue locks, custom routines exist which areĬopies of each and every Postgres lock routine. I) Resource queues share the same lock tables in shared memory used by ALL So, it is an apt time to bring up the cause for deprecation. We already have 2 major versions supporting resource groups. Resource groups were released in GP5, which provide superior functionality to GP7 (and add deprecation notices to GP6):ġ. Reasons why we should remove the resource queue feature from We have the following proposal to remove the resource queue feature from GP7
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