[CBRD-20697] Ordered fix: prevent unfixed page from being deallocated

[ribram]

http://jira.cubrid.org/browse/CBRD-20697

This issue is that vacuum deallocated pages unfixed by ordered fix. Active worker wants to advance during heap scan from a page to next page. Next page has higher priority, so current page must be unfixed. A vacuum worker fixes page and deallocates it before active worker fixes it again.

[razvanradulescu]

I agree with the fix

[eseokoh]

I think we have manage mutexes for hash_anchor and bcb, and would like propose the change as follows:

  for (i = 0; i < saved_pages_cnt; i++)
    {
      if (ordered_holders_info[i].prevent_dealloc)
        {
          /* we need to remove prevent deallocate. */
          PGBUF_BUFFER_HASH *hash_anchor = &pgbuf_Pool.buf_hash_table[PGBUF_HASH_VALUE (&ordered_holders_info[i].vpid)];
          bufptr = pgbuf_search_hash_chain (hash_anchor, &ordered_holders_info[i].vpid);

          if (bufptr == NULL)
            {
              /* oops... no longer in buffer?? */
              assert (false);
              pthread_mutex_unlock (&hash_anchor->hash_mutex);
              continue;
            }

          if (bufptr->avoid_dealloc_cnt <= 0)
            {
              /* oops... deallocate not prevented */
              assert (false);
            }
          else
            {
              ATOMIC_INC_32 (&bufptr->avoid_dealloc_cnt, -1);
            }

          PGBUF_BCB_UNLOCK (bufptr);
        }
    }

We may have to also confirm the case: bufptr == NULL
This case means that bcb was victimized by the other. It is very unlikely, but I'm not 100% sure.
Can you confirm it?

[ribram]

Yes, I have made the required changes :).