Hi, Kevin sir! On 1 June 2017 at 02:20, Kevin Grittner <kgri...@gmail.com> wrote:
> On Wed, May 31, 2017 at 3:02 PM, Shubham Barai <shubhambara...@gmail.com> > wrote: > > > I have been accepted as GSoC student for the project "Explicitly support > > predicate locks in index access methods besides b-tree". I want to share > my > > approach for implementation of page level predicate locking in gist > index. > > For the benefit of all following the discussion, implementing > support in an index AM conceptually consists of two things: > (1) Any scan with user-visible results must create SIRead predicate > locks on "gaps" scanned. (For example, a scan just to find an > insertion spot for an index entry does not generally count, whereas > a scan to satisfy a user "EXISTS" test does.) > (2) Any insert into the index must CheckForSerializableConflictIn() > at enough points that at least one of them will detect an overlap > with a predicate lock from a preceding scan if the inserted index > entry might have changed the results of that preceding scan. > > Detecting such a conflict does not automatically result in a > serialization failure, but is only part of tracking the information > necessary to make such a determination. All that is handled by the > existing machinery if the AM does the above. > > With a btree index, locking gaps at the leaf level is normally > sufficient, because both scan and insertion of an index entry must > descend that far. > > > The main difference between b-tree and gist index while searching for a > > target tuple is that in gist index, we can determine if there is a match > or > > not at any level of the index. > > Agreed. A gist scan can fail at any level, but for that scan to > have produced a different result due to insertion of an index entry, > *some* page that the scan looked at must be modified. > > > The simplest way to do that will be by inserting a call for > > prdicatelockpage() in gistscanpage(). > > Yup. > > > Insertion algorithm also needs to check for conflicting predicate locks > at > > each level of the index. > > Yup. > > > We can insert a call for CheckForSerializableConflictIn() at two places > in > > gistdoinsert(). > > > > 1. after acquiring an exclusive lock on internal page (in case we are > trying > > to replace an old search key) > > > > 2. after acquiring an exclusive lock on leaf page > > > > If there is not enough space for insertion, we have to copy predicate > lock > > from an old page to all new pages generated after a successful split > > operation. For that, we can insert a call for PredicateLockPageSplit() in > > gistplacetopage(). > > That all sounds good. When you code a patch, don't forget to add > tests to src/test/isolation. > > Do you need any help getting a development/build/test environment > set up? > Yes, any link to the documentation will be helpful. > > -- > Kevin Grittner > VMware vCenter Server > https://www.vmware.com/ >
