Re: [HACKERS] Page Scan Mode in Hash Index

On Wed, Sep 20, 2017 at 5:37 AM, Ashutosh Sharma <ashu.coek88@gmail.com> wrote:
> Thanks for all your review comments. Please find my comments in-line.

+            if (!BlockNumberIsValid(opaque->hasho_nextblkno))
+            {
+                if (so->currPos.buf == so->hashso_bucket_buf ||
+                    so->currPos.buf == so->hashso_split_bucket_buf)
+                    prev_blkno = InvalidBlockNumber;
+                else
+                    prev_blkno = opaque->hasho_prevblkno;
+            }

1. Why not remove the outer "if" statement?

2. How about adding a comment, like /* If this is a primary bucket
page, hasho_prevblkno is not a real block number. */

> When _hash_readpage() doesn't find any qualifying tuples i.e. when
> _hash_readnext() returns Invalid buffer, we just update prevPage,
> nextPage and buf in
> currPos (not currPage or lsn) as currPage and lsn should point to last
> page in the hash bucket so that we can mark the killed items as dead
> at the end of scan (with the help of _hash_kill_items). Hence, we keep
> the currpage and lsn as it is if no more valid hash pages are found.

How about adding a comment about this, by extending this comment:

+                 * Remember next and previous block numbers for scrollable
+                 * cursors to know the start position and return FALSE
+                 * indicating that no more matching tuples were found.

e.g. (Don't reset currPage or lsn, because we expect _hash_kill_items
to be called for the old page after this function returns.)

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company


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