Re: contrib/cache_scan (Re: What's needed for cache-only table scan?)

2014-02-12 14:59 GMT+09:00 Haribabu Kommi <kommi.haribabu@gmail.com>:

> 7. In ccache_find_tuple function this Assert(i_min + 1 < cchunk->ntups); can

> go wrong when only one tuple present in the block
>    with the equal item pointer what we are searching in the forward scan
> direction.
>

It shouldn't happen, because the first or second ItemPointerCompare will
handle the condition. Please assume the cchunk->ntups == 1. In this case,
any given ctid shall match either of them, because any ctid is less, equal or
larger to the tuple being only cached, thus, it moves to the right or left node
according to the scan direction.

> 8. I am not able to find a protection mechanism in insert/delete and etc of
> a tuple in Ttree. As this is a shared memory it can cause problems.
>

For design simplification, I put a giant lock per columnar-cache.
So, routines in cscan.c acquires exclusive lwlock prior to invocation of
ccache_insert_tuple / ccache_delete_tuple.