Re: [COMMITTERS] pgsql: Move each SLRU's lwlocks to a separate tranche.

On Fri, Mar 25, 2016 at 9:48 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> It's stupid that we keep spending time and energy figuring out which
>> shared memory data structures require alignment and which ones don't.
>> Let's just align them *all* and be done with it.  The memory cost
>> shouldn't be more than a few kB.
>
> I think such a proposal should come with a measurement, not just
> speculation about what it costs.

About 6kB with default settings.  See below.

LOG:  shared memory size: 148471808
LOG:  size 48 -> maxalign 48, cachelinealign 128, delta 80
LOG:  size 25988 -> maxalign 25992, cachelinealign 26112, delta 120
LOG:  size 2904 -> maxalign 2904, cachelinealign 2944, delta 40
LOG:  size 264 -> maxalign 264, cachelinealign 384, delta 120
LOG:  size 4209296 -> maxalign 4209296, cachelinealign 4209408, delta 112
LOG:  size 529216 -> maxalign 529216, cachelinealign 529280, delta 64
LOG:  size 133600 -> maxalign 133600, cachelinealign 133632, delta 32
LOG:  size 32 -> maxalign 32, cachelinealign 128, delta 96
LOG:  size 267072 -> maxalign 267072, cachelinealign 267136, delta 64
LOG:  size 66880 -> maxalign 66880, cachelinealign 66944, delta 64
LOG:  size 133600 -> maxalign 133600, cachelinealign 133632, delta 32
LOG:  size 948 -> maxalign 952, cachelinealign 1024, delta 72
LOG:  size 2904 -> maxalign 2904, cachelinealign 2944, delta 40
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 20640 -> maxalign 20640, cachelinealign 20736, delta 96
LOG:  size 28 -> maxalign 32, cachelinealign 128, delta 96
LOG:  size 2904 -> maxalign 2904, cachelinealign 2944, delta 40
LOG:  size 2904 -> maxalign 2904, cachelinealign 2944, delta 40
LOG:  size 4100 -> maxalign 4104, cachelinealign 4224, delta 120
LOG:  size 2904 -> maxalign 2904, cachelinealign 2944, delta 40
LOG:  size 2904 -> maxalign 2904, cachelinealign 2944, delta 40
LOG:  size 88 -> maxalign 88, cachelinealign 128, delta 40
LOG:  size 2904 -> maxalign 2904, cachelinealign 2944, delta 40
LOG:  size 24 -> maxalign 24, cachelinealign 128, delta 104
LOG:  size 16 -> maxalign 16, cachelinealign 128, delta 112
LOG:  size 133600 -> maxalign 133600, cachelinealign 133632, delta 32
LOG:  size 16 -> maxalign 16, cachelinealign 128, delta 112
LOG:  size 96 -> maxalign 96, cachelinealign 128, delta 32
LOG:  size 95584 -> maxalign 95584, cachelinealign 95616, delta 32
LOG:  size 1392 -> maxalign 1392, cachelinealign 1408, delta 16
LOG:  size 1 -> maxalign 8, cachelinealign 128, delta 120
LOG:  size 488 -> maxalign 488, cachelinealign 512, delta 24
LOG:  size 16 -> maxalign 16, cachelinealign 128, delta 112
LOG:  size 3016 -> maxalign 3016, cachelinealign 3072, delta 56
LOG:  size 69144 -> maxalign 69144, cachelinealign 69248, delta 104
LOG:  size 940 -> maxalign 944, cachelinealign 1024, delta 80
LOG:  size 4760 -> maxalign 4760, cachelinealign 4864, delta 104
LOG:  size 327720 -> maxalign 327720, cachelinealign 327808, delta 88
LOG:  size 224 -> maxalign 224, cachelinealign 256, delta 32
LOG:  size 56 -> maxalign 56, cachelinealign 128, delta 72
LOG:  size 1192 -> maxalign 1192, cachelinealign 1280, delta 88
LOG:  size 1356 -> maxalign 1360, cachelinealign 1408, delta 48
LOG:  size 656 -> maxalign 656, cachelinealign 768, delta 112
LOG:  size 1832 -> maxalign 1832, cachelinealign 1920, delta 88
LOG:  size 66880 -> maxalign 66880, cachelinealign 66944, delta 64
LOG:  total additional space consumed due to cache line alignment = 6096

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