Hash table inefficiencies

[Ian2327]

Proposed Changes

Current state of hash table bucket halving. Currently implemented in hash_table.h under HASH_TABLE_ITERATE

Merge Checklist

The following items must be completed before PRs can be merged.
Check these off to verify you have completed all steps.

• make test Run local tests prior to pushing.
• make format Format source code to comply with lint policies. Note that some lint errors can only be resolved manually (e.g., Python)
• make lint Run lint on source code prior to pushing.
• Manual Update: Update the manual to reflect user-visible changes.
• Type Labels: Select a github label for the type: bugfix, enhancement, etc.
• Product Labels: Select a github label for the product: TaskVine, Makeflow, etc.
• PR RTM: Mark your PR as ready to merge.

[btovar]

Updated benchmarks (calling reduce table on hash_table_remove). Note that the timings for adding and removing are pretty similar now. For each step, (2^i - 1) entries are added or removed. Every time an entry is added or removed, the benchmark calls HASH_TABLE_ITERATE.

INSERTION PHASE:
step   0 size          1 load_max 0.007874 load_now 0.007874 time 0.000001
step   1 size          3 load_max 0.023622 load_now 0.023622 time 0.000001
step   2 size          7 load_max 0.055118 load_now 0.055118 time 0.000002
step   3 size         15 load_max 0.118110 load_now 0.118110 time 0.000004
step   4 size         31 load_max 0.244094 load_now 0.244094 time 0.000010
step   5 size         63 load_max 0.496063 load_now 0.496063 time 0.000023
step   6 size        127 load_max 0.755906 load_now 0.498039 time 0.000074
step   7 size        255 load_max 0.752941 load_now 0.499022 time 0.000309
step   8 size        511 load_max 0.751468 load_now 0.499511 time 0.001174
step   9 size       1023 load_max 0.750733 load_now 0.499756 time 0.004688
step  10 size       2047 load_max 0.750366 load_now 0.499878 time 0.020509
step  11 size       4095 load_max 0.750183 load_now 0.499939 time 0.112303
step  12 size       8191 load_max 0.750092 load_now 0.499969 time 0.613042
step  13 size      16383 load_max 0.750046 load_now 0.499985 time 2.777665
step  14 size      32767 load_max 0.750023 load_now 0.499992 time 11.401937
step  15 size      65535 load_max 0.750011 load_now 0.499996 time 45.774249
REMOVAL PHASE:
step  15 size      32767 load_min 0.249994 load_now 0.249994 time 49.533629
step  14 size      16383 load_min 0.124993 load_now 0.124993 time 15.401450
step  13 size       8191 load_min 0.062493 load_now 0.062493 time 5.421695
step  12 size       4095 load_min 0.031243 load_now 0.031243 time 2.160678
step  11 size       2047 load_min 0.015617 load_now 0.015617 time 0.945477
step  10 size       1023 load_min 0.007805 load_now 0.007805 time 0.440412
step   9 size        511 load_min 0.003899 load_now 0.003899 time 0.211325
step   8 size        255 load_min 0.001946 load_now 0.001946 time 0.103570
step   7 size        127 load_min 0.000969 load_now 0.000969 time 0.051359
step   6 size         63 load_min 0.000481 load_now 0.000481 time 0.025469
step   5 size         31 load_min 0.000237 load_now 0.000237 time 0.012639
step   4 size         15 load_min 0.000114 load_now 0.000114 time 0.006320
step   3 size          7 load_min 0.000053 load_now 0.000053 time 0.003150
step   2 size          3 load_min 0.000023 load_now 0.000023 time 0.001588
step   1 size          1 load_min 0.000008 load_now 0.000008 time 0.000810
step   0 size          0 load_min 0.000000 load_now 0.000000 time 0.000407

[btovar]

Doubling and halving with reusing old entries (less mallocs) does make a difference:
(about 10s for the case of 64K entries)

INSERTION PHASE:
step   0 size        1 buckets      127 load_max 0.007874 load_now 0.007874 time 0.000001 time_norm 0.000001
step   1 size        3 buckets      127 load_max 0.023622 load_now 0.023622 time 0.000001 time_norm 0.000000
step   2 size        7 buckets      127 load_max 0.055118 load_now 0.055118 time 0.000001 time_norm 0.000000
step   3 size       15 buckets      127 load_max 0.118110 load_now 0.118110 time 0.000003 time_norm 0.000000
step   4 size       31 buckets      127 load_max 0.244094 load_now 0.244094 time 0.000007 time_norm 0.000000
step   5 size       63 buckets      127 load_max 0.496063 load_now 0.496063 time 0.000017 time_norm 0.000001
step   6 size      127 buckets      255 load_max 0.755906 load_now 0.498039 time 0.000057 time_norm 0.000001
step   7 size      255 buckets      511 load_max 0.752941 load_now 0.499022 time 0.000217 time_norm 0.000002
step   8 size      511 buckets     1023 load_max 0.751468 load_now 0.499511 time 0.000843 time_norm 0.000003
step   9 size     1023 buckets     2047 load_max 0.750733 load_now 0.499756 time 0.003290 time_norm 0.000006
step  10 size     2047 buckets     4095 load_max 0.750366 load_now 0.499878 time 0.013082 time_norm 0.000013
step  11 size     4095 buckets     8191 load_max 0.750183 load_now 0.499939 time 0.058701 time_norm 0.000029
step  12 size     8191 buckets    16383 load_max 0.750092 load_now 0.499969 time 0.380795 time_norm 0.000093
step  13 size    16383 buckets    32767 load_max 0.750046 load_now 0.499985 time 1.938658 time_norm 0.000237
step  14 size    32767 buckets    65535 load_max 0.750023 load_now 0.499992 time 8.082540 time_norm 0.000493
step  15 size    65535 buckets   131071 load_max 0.750011 load_now 0.499996 time 32.875638 time_norm 0.001003
REMOVAL PHASE:
step  15 size    32767 buckets   131071 load_min 0.249994 load_now 0.249994 time 35.550363 time_norm 0.001085
step  14 size    16383 buckets    65535 load_min 0.125001 load_now 0.249989 time 11.423033 time_norm 0.000697
step  13 size     8191 buckets    32767 load_min 0.125002 load_now 0.249977 time 2.761504 time_norm 0.000337
step  12 size     4095 buckets    16383 load_min 0.125004 load_now 0.249954 time 0.610764 time_norm 0.000149
step  11 size     2047 buckets     8191 load_min 0.125008 load_now 0.249908 time 0.117709 time_norm 0.000057
step  10 size     1023 buckets     4095 load_min 0.125015 load_now 0.249817 time 0.024749 time_norm 0.000024
step   9 size      511 buckets     2047 load_min 0.125031 load_now 0.249634 time 0.005994 time_norm 0.000012
step   8 size      255 buckets     1023 load_min 0.125061 load_now 0.249267 time 0.001561 time_norm 0.000006
step   7 size      127 buckets      511 load_min 0.125122 load_now 0.248532 time 0.000382 time_norm 0.000003
step   6 size       63 buckets      255 load_min 0.125245 load_now 0.247059 time 0.000103 time_norm 0.000002
step   5 size       31 buckets      127 load_min 0.125490 load_now 0.244094 time 0.000026 time_norm 0.000001
step   4 size       15 buckets      127 load_min 0.118110 load_now 0.118110 time 0.000010 time_norm 0.000001
step   3 size        7 buckets      127 load_min 0.055118 load_now 0.055118 time 0.000004 time_norm 0.000001
step   2 size        3 buckets      127 load_min 0.023622 load_now 0.023622 time 0.000002 time_norm 0.000001
step   1 size        1 buckets      127 load_min 0.007874 load_now 0.007874 time 0.000001 time_norm 0.000001