On Fri, Feb 25, 2022 at 8:54 AM Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Fri, Feb 25, 2022 at 4:41 AM Melanie Plageman > <melanieplage...@gmail.com> wrote: > > > > I'm trying to understand why hash indexes are built primarily in shared > > buffers except when allocating a new splitpoint's worth of bucket pages > > -- which is done with smgrextend() directly in _hash_alloc_buckets(). > > > > Is this just so that the value returned by smgrnblocks() includes the > > new splitpoint's worth of bucket pages? > > > > All writes of tuple data to pages in this new splitpoint will go > > through shared buffers (via hash_getnewbuf()). > > > > I asked this and got some thoughts from Robert in [1], but I still don't > > really get it. > > > > When a new page is needed during the hash index build, why can't > > _hash_expandtable() just call ReadBufferExtended() with P_NEW instead of > > _hash_getnewbuf()? Does it have to do with the BUCKET_TO_BLKNO mapping? > > > > We allocate the chunk of pages (power-of-2 groups) at the time of > split which allows them to appear consecutively in an index. >
I think allocating chunks of pages via "ReadBufferExtended() with P_NEW" will be time-consuming as compared to what we do now. -- With Regards, Amit Kapila.
