Hi guys, My name is Shubham Barai and I am a final year student at Maharashtra Institute of Technology, Pune, India. I am very interested in contributing Postgresql this year through GSoC project.
I am particularly interested in working on the project "Explicitly support predicate locks in index access methods besides btree". I have gone through some research papers which were recommended on https://wiki.postgresql. org/wiki/GSoC_2017 to understand the concept of Serializable Snapshot Isolation used in PostgreSQL. I have also browsed through the codebase to get some idea of different access methods for gin, gist, and hash indexes. I want to discuss my proposal to get some feedback before I write my final proposal. Sorry, I am discussing my proposal little late. I was really busy in my academics. Currently, only B+-trees support page level predicate locking.For other indexes, it acquires relation level lock which can lead to unnecessary serialization failure due to rw dependency caused by any insert into the index. So, the main task of this project is to support page level predicate locking for remaining indexes. * Gist Index B+tree index acquires predicate locks only on leaf pages as index tuples with record pointers are stored on leaf pages. But for Gist index, we have to consider locking at each index level as index tuples can be stored in buffers associated with internal pages or in leaf pages. So, the functions where we need to insert a call for 1. PredicateLockPage() ->gistScanPage() after acquiring a shared lock on a buffer 2.CheckForSerializableConflictIn() -> gistdoinsert() after acquiring an exclusive lock on a target buffer and before inserting a tuple 3. PredicateLockPageSplit() ->gistplacetopage() If there is not enough space for insertion, we need to copy predicate lock from an old page to all new pages generated after a successful split operation. PredicateLockPageSplit(Relation relation, BlockNumber oldblkno, BlockNumber a lot) is used by b+-tree where two pages are involved in a split operation. For Gist index, we can define a similar function where more than one page can be generated after split operation. * Gin Index Gin index consists of a B-tree index over key values, where each key is an element of some indexed items and each tuple in a leaf page contains either a posting list if the list is small enough or a pointer to posting tree. 1. PredicateLockPage() ->startscanentry() before calling collectMatchBitmap() ->scanPostingTree() after acquiring a shared lock on a leaf page 2.CheckForSerializableConflictIn() -> ginentryinsert() ->gininsertitempointers() in case of insertion in a posting tree 3. PredicateLockPageSplit() -> dataBeginPlacetoPageLeaf() after calling dataPlacetoPageLeafSplit() * Hash Index 1. PredicateLockPage() ->hashgettuple() ->_hash_first() ->_hash_readnext() ->_hash_readprev() 2.CheckForSerializableConflictIn() -> _hash_doinsert() 3. PredicateLockPageSplit() currently, I am trying to understand how the splitting of bucket works. should we acquire predicate lock on every page from an old and new bucket in case there is a predicate lock on a page of an old bucket? There may be a lot of other places where we need to insert function calls for predicate locking that I haven't included yet. I didn't go into details of every index AM. can anyone help me find existing tests for b-tree? Regards, Shubham