Re: copy.c allocation constant

On Thu, Jan 25, 2018 at 9:35 AM, Bruce Momjian <bruce@momjian.us> wrote:
> The BSD memory allocator used to allocate in powers of two, and keep the
> header in a separate location.  They did this so they could combine two
> free, identically-sized memory blocks into a single one that was double
> the size.  I have no idea how it works now.

According to "man malloc" on my FreeBSD 11.1 box (which uses jemalloc,
I think NetBSD and OpenBSD use something else), the code Andrew showed
at the top of this thread will waste ~16kB (because it'll round up to
80kB) and nodeHash.c will waste ~8kB for every ~32kB chunk of tuples
as described in that other thread.

       +----------------------------------------------------------+
       |Category   Spacing   Size                                 |
       |Small           lg   [8]                                  |
       |                16   [16, 32, 48, 64, 80, 96, 112, 128]   |
       |                32   [160, 192, 224, 256]                 |
       |                64   [320, 384, 448, 512]                 |
       |               128   [640, 768, 896, 1024]                |
       |               256   [1280, 1536, 1792, 2048]             |
       |               512   [2560, 3072, 3584, 4096]             |
       |             1 KiB   [5 KiB, 6 KiB, 7 KiB, 8 KiB]         |
       |             2 KiB   [10 KiB, 12 KiB, 14 KiB]             |
       |Large        2 KiB   [16 KiB]                             |
       |             4 KiB   [20 KiB, 24 KiB, 28 KiB, 32 KiB]     |
       |             8 KiB   [40 KiB, 48 KiB, 54 KiB, 64 KiB]     |
       |            16 KiB   [80 KiB, 96 KiB, 112 KiB, 128 KiB]   |
       |            32 KiB   [160 KiB, 192 KiB, 224 KiB, 256 KiB] |
       |            64 KiB   [320 KiB, 384 KiB, 448 KiB, 512 KiB] |
       |           128 KiB   [640 KiB, 768 KiB, 896 KiB, 1 MiB]   |
       |           256 KiB   [1280 KiB, 1536 KiB, 1792 KiB]       |
       |Huge       256 KiB   [2 MiB]                              |
       |           512 KiB   [2560 KiB, 3 MiB, 3584 KiB, 4 MiB]   |
       |             1 MiB   [5 MiB, 6 MiB, 7 MiB, 8 MiB]         |
       |             2 MiB   [10 MiB, 12 MiB, 14 MiB, 16 MiB]     |
       |             4 MiB   [20 MiB, 24 MiB, 28 MiB, 32 MiB]     |
       |             8 MiB   [40 MiB, 48 MiB, 56 MiB, 64 MiB]     |
       |               ...   ...                                  |
       |           512 PiB   [2560 PiB, 3 EiB, 3584 PiB, 4 EiB]   |
       |             1 EiB   [5 EiB, 6 EiB, 7 EiB]                |
       +----------------------------------------------------------+

-- 
Thomas Munro
http://www.enterprisedb.com