How to debug frozen solver?

Hi I have a problem with solver getting stuck at Root relaxation - it stays there for 2h without any progress. Any ideas?

m.params.Presolve = 2
m.params.PreSparsify = 1
m.params.NodefileStart = 0.5
m.params.Threads = 8
m.params.LogFile = add_timestamp_to_filename('logs/GRB_opt.txt')
m.params.DegenMoves = 0

CPU model: Intel(R) Xeon(R) CPU @ 2.80GHz, instruction set [SSE2|AVX|AVX2|AVX512]
Thread count: 24 physical cores, 48 logical processors, using up to 8 threads

WLS license 2543206 - registered to Nexocode
Optimize a model with 60561680 rows, 55516429 columns and 132824384 nonzeros
Model fingerprint: 0x6eba6ced
Model has 14042 general constraints
Variable types: 443751 continuous, 55072678 integer (50705781 binary)
Coefficient statistics:
  Matrix range     [1e+00, 1e+03]
  Objective range  [1e+00, 1e+00]
  Bounds range     [1e+00, 1e+00]
  RHS range        [1e+00, 2e+04]
Found heuristic solution: objective 8.591800e+14
Presolve removed 0 rows and 0 columns (presolve time = 7s) ...
Presolve removed 0 rows and 0 columns (presolve time = 11s) ...
Presolve removed 722398 rows and 14161 columns (presolve time = 18s) ...
Presolve removed 730539 rows and 14280 columns (presolve time = 21s) ...
Presolve removed 736001 rows and 310020 columns (presolve time = 25s) ...
Presolve removed 736001 rows and 46635743 columns (presolve time = 44s) ...
Presolve removed 97753344 rows and 46635743 columns (presolve time = 45s) ...
Presolve removed 97753344 rows and 46635743 columns (presolve time = 53s) ...
Presolve removed 47061724 rows and 46635743 columns
Presolve time: 52.65s
Presolved: 13499956 rows, 8880686 columns, 39426392 nonzeros
Found heuristic solution: objective 5.002538e+07
Variable types: 133677 continuous, 8747009 integer (7010725 binary)
Root relaxation presolve removed 34 rows and 34 columns (presolve time = 5s) ...
Root relaxation presolve removed 34 rows and 34 columns (presolve time = 10s) ...
Root relaxation presolve removed 34 rows and 34 columns (presolve time = 15s) ...
Root relaxation presolve removed 34 rows and 34 columns (presolve time = 20s) ...
Root relaxation presolve removed 34 rows and 34 columns (presolve time = 25s) ...
Root relaxation presolve removed 34 rows and 34 columns (presolve time = 30s) ...
Root relaxation presolve removed 34 rows and 34 columns (presolve time = 35s) ...
Root relaxation presolve removed 34 rows and 34 columns (presolve time = 40s) ...
Root relaxation presolve removed 34 rows and 34 columns (presolve time = 46s) ...
Root relaxation presolve removed 34 rows and 34 columns (presolve time = 50s) ...
Root relaxation presolve removed 34 rows and 34 columns
Root relaxation presolved: 4629965 rows, 4634825 columns, 17707188 nonzeros

Deterministic concurrent LP optimizer: primal simplex, dual simplex, and barrier
Showing barrier log only...

Root barrier log...

Elapsed ordering time = 19s
Elapsed ordering time = 22s
Elapsed ordering time = 25s
Elapsed ordering time = 30s
Elapsed ordering time = 35s
Elapsed ordering time = 40s
Elapsed ordering time = 45s
Elapsed ordering time = 50s
Elapsed ordering time = 55s
Elapsed ordering time = 60s
Elapsed ordering time = 65s
Elapsed ordering time = 70s
Elapsed ordering time = 75s
Elapsed ordering time = 80s
Elapsed ordering time = 85s
Elapsed ordering time = 90s
Elapsed ordering time = 95s
Elapsed ordering time = 100s
Elapsed ordering time = 105s
Elapsed ordering time = 110s
Elapsed ordering time = 115s
Elapsed ordering time = 120s
Elapsed ordering time = 125s
Elapsed ordering time = 130s
Elapsed ordering time = 135s
Elapsed ordering time = 140s
Elapsed ordering time = 145s
Elapsed ordering time = 150s
Elapsed ordering time = 155s
Elapsed ordering time = 160s
Elapsed ordering time = 165s
Elapsed ordering time = 170s
Elapsed ordering time = 175s
Elapsed ordering time = 180s
Elapsed ordering time = 185s
Elapsed ordering time = 190s
Elapsed ordering time = 195s
Elapsed ordering time = 200s
Elapsed ordering time = 205s
Elapsed ordering time = 210s
Elapsed ordering time = 215s
Elapsed ordering time = 220s
Elapsed ordering time = 225s
Elapsed ordering time = 230s
Elapsed ordering time = 235s
Elapsed ordering time = 240s
Elapsed ordering time = 245s
Elapsed ordering time = 250s
Elapsed ordering time = 255s
Elapsed ordering time = 260s
Elapsed ordering time = 265s
Elapsed ordering time = 270s
Elapsed ordering time = 275s
Elapsed ordering time = 280s
Elapsed ordering time = 313s
Elapsed ordering time = 315s
Elapsed ordering time = 320s
Elapsed ordering time = 325s
Ordering time: 838.67s
Elapsed ordering time = 839s
Elapsed ordering time = 840s
Elapsed ordering time = 845s
Elapsed ordering time = 850s
Elapsed ordering time = 855s
Elapsed ordering time = 860s
Elapsed ordering time = 865s
Elapsed ordering time = 870s
Elapsed ordering time = 875s
Elapsed ordering time = 880s
Elapsed ordering time = 885s
Elapsed ordering time = 890s
Elapsed ordering time = 895s
Elapsed ordering time = 900s
Ordering time: 908.07s

Barrier statistics:
 Dense cols : 13225
 AA' NZ     : 1.742e+07
 Factor NZ  : 2.565e+08 (roughly 6.0 GB of memory)
 Factor Ops : 1.079e+12 (roughly 6 seconds per iteration)
 Threads    : 6

                  Objective                Residual
Iter       Primal          Dual         Primal    Dual     Compl     Time
   0   1.22244919e+09 -6.81588642e+09  5.92e+03 2.65e+02  9.06e+04  1371s
   1   1.19094833e+09 -6.93573859e+09  5.71e+03 9.96e+02  8.25e+04  1380s
   2   1.12402383e+09 -7.55600633e+09  5.25e+03 1.48e+03  7.84e+04  1389s
   3   7.25843525e+08 -8.37559832e+09  3.00e+03 8.54e+02  4.70e+04  1399s
   4   1.43538171e+08 -9.05683853e+09  3.44e+02 1.83e+00  6.14e+03  1411s
   5   6.60118868e+07 -6.66387784e+09  9.22e+01 1.35e+00  1.82e+03  1425s
   6   4.29623838e+07 -3.16812403e+09  1.54e+01 9.70e-01  4.10e+02  1440s
   7   3.78905904e+07 -8.18539311e+08  2.11e+00 2.51e-01  7.54e+01  1454s
   8   3.53962295e+07 -1.40811914e+08  4.50e-01 3.53e-02  1.37e+01  1466s
   9   3.40602119e+07 -3.98061845e+07  2.41e-01 1.31e-02  5.58e+00  1476s
  10   3.36071360e+07 -2.64158820e+07  1.88e-01 1.06e-02  4.50e+00  1485s
  11   3.33476404e+07 -1.95361227e+07  1.59e-01 9.32e-03  3.94e+00  1493s
  12   3.32959745e+07 -1.35761238e+07  1.53e-01 8.13e-03  3.49e+00  1501s
  13   3.29926118e+07 -7.13840850e+06  1.22e-01 6.95e-03  2.98e+00  1509s
  14   3.27056670e+07  8.52086671e+06  9.57e-02 4.19e-03  1.79e+00  1518s
  15   3.26283181e+07  1.14558509e+07  8.94e-02 3.65e-03  1.56e+00  1528s
  16   3.24229144e+07  1.74068697e+07  7.49e-02 2.56e-03  1.11e+00  1540s
  17   3.23906760e+07  1.76552072e+07  7.15e-02 2.52e-03  1.08e+00  1550s
  18   3.23523320e+07  1.92521938e+07  6.77e-02 2.23e-03  9.63e-01  1562s
  19   3.21305914e+07  2.32306306e+07  4.94e-02 1.48e-03  6.52e-01  1579s
  20   3.20510189e+07  2.45716590e+07  4.15e-02 1.24e-03  5.47e-01  1594s
  21   3.19834798e+07  2.63968825e+07  3.35e-02 9.15e-04  4.08e-01  1608s
  22   3.19592584e+07  2.71983551e+07  3.09e-02 7.73e-04  3.48e-01  1621s
  23   3.19351880e+07  2.78535951e+07  2.84e-02 6.59e-04  2.98e-01  1636s
  24   3.18825998e+07  2.92514487e+07  2.32e-02 4.14e-04  1.92e-01  1651s
  25   3.18525625e+07  2.98680575e+07  2.02e-02 3.07e-04  1.45e-01  1665s
  26   3.18127915e+07  3.00915416e+07  1.56e-02 2.69e-04  1.25e-01  1680s
  27   3.17964968e+07  3.04121565e+07  1.39e-02 2.14e-04  1.01e-01  1695s
  28   3.17748483e+07  3.06496220e+07  1.12e-02 1.73e-04  8.19e-02  1708s
  29   3.17552467e+07  3.10292130e+07  8.87e-03 1.09e-04  5.29e-02  1723s
  30   3.17464118e+07  3.12007845e+07  7.75e-03 8.05e-05  3.97e-02  1738s
  31   3.17401670e+07  3.13092930e+07  6.91e-03 6.24e-05  3.14e-02  1753s
  32   3.17223945e+07  3.15537267e+07  4.38e-03 2.23e-05  1.23e-02  1767s
  33   3.17159461e+07  3.15952570e+07  3.35e-03 1.56e-05  8.79e-03  1781s
  34   3.17150281e+07  3.16015385e+07  3.22e-03 1.46e-05  8.27e-03  1797s
  35   3.17097189e+07  3.16260534e+07  2.36e-03 1.07e-05  6.09e-03  1810s
  36   3.17046144e+07  3.16590320e+07  1.53e-03 5.25e-06  3.32e-03  1822s
  37   3.16951985e+07  3.16942277e+07  1.86e-06 7.71e-08  7.05e-05  1835s
  38   3.16951750e+07  3.16951384e+07  7.40e-11 2.90e-09  2.66e-06  1850s
  39   3.16951750e+07  3.16951749e+07  2.58e-11 1.02e-11  2.66e-09  1862s

Barrier solved model in 39 iterations and 1861.80 seconds (1370.75 work units)
Optimal objective 3.16951750e+07


Root crossover log...

   48905 DPushes remaining with DInf 0.0000000e+00              1869s
     215 DPushes remaining with DInf 0.0000000e+00              1871s
       0 DPushes remaining with DInf 0.0000000e+00              1872s

 4341107 PPushes remaining with PInf 0.0000000e+00              1873s
 3590623 PPushes remaining with PInf 0.0000000e+00              1875s
 2632104 PPushes remaining with PInf 0.0000000e+00              1881s
 2174408 PPushes remaining with PInf 0.0000000e+00              1885s
 1839326 PPushes remaining with PInf 0.0000000e+00              1890s
 1580771 PPushes remaining with PInf 0.0000000e+00              1896s
 1357750 PPushes remaining with PInf 0.0000000e+00              1901s
 1169415 PPushes remaining with PInf 0.0000000e+00              1905s
 1003536 PPushes remaining with PInf 0.0000000e+00              1910s
  862037 PPushes remaining with PInf 0.0000000e+00              1915s
  717770 PPushes remaining with PInf 0.0000000e+00              1921s
  620841 PPushes remaining with PInf 0.0000000e+00              1926s
  537886 PPushes remaining with PInf 0.0000000e+00              1930s
  451111 PPushes remaining with PInf 0.0000000e+00              1936s
  391527 PPushes remaining with PInf 0.0000000e+00              1940s
  330227 PPushes remaining with PInf 0.0000000e+00              1946s
  288667 PPushes remaining with PInf 0.0000000e+00              1950s
  245300 PPushes remaining with PInf 0.0000000e+00              1956s
  216869 PPushes remaining with PInf 0.0000000e+00              1960s
  186482 PPushes remaining with PInf 0.0000000e+00              1966s
  164758 PPushes remaining with PInf 0.0000000e+00              1970s
  143325 PPushes remaining with PInf 0.0000000e+00              1976s
  129520 PPushes remaining with PInf 0.0000000e+00              1980s
  113880 PPushes remaining with PInf 0.0000000e+00              1986s
  103456 PPushes remaining with PInf 0.0000000e+00              1990s
   91825 PPushes remaining with PInf 0.0000000e+00              1996s
   19774 PPushes remaining with PInf 0.0000000e+00              2016s
   10779 PPushes remaining with PInf 0.0000000e+00              2033s
    9780 PPushes remaining with PInf 0.0000000e+00              2063s
    8781 PPushes remaining with PInf 0.0000000e+00              2104s
    7782 PPushes remaining with PInf 0.0000000e+00              2152s
    6783 PPushes remaining with PInf 0.0000000e+00              2212s
    5784 PPushes remaining with PInf 0.0000000e+00              2288s
    4785 PPushes remaining with PInf 0.0000000e+00              2376s
    3786 PPushes remaining with PInf 0.0000000e+00              2478s
    2787 PPushes remaining with PInf 0.0000000e+00              2603s
    1788 PPushes remaining with PInf 0.0000000e+00              2748s
     789 PPushes remaining with PInf 0.0000000e+00              2923s
       0 PPushes remaining with PInf 0.0000000e+00              3080s

  Push phase complete: Pinf 0.0000000e+00, Dinf 1.2404266e-05   3081s


Root simplex log...

Iteration    Objective       Primal Inf.    Dual Inf.      Time
 4383819    3.1695175e+07   0.000000e+00   0.000000e+00   3130s
Waiting for other threads to finish...        3195s
Waiting for other threads to finish...        3259s
Waiting for other threads to finish...        3322s
Waiting for other threads to finish...        3386s
Waiting for other threads to finish...        3450s
Waiting for other threads to finish...        3514s
Waiting for other threads to finish...        3578s
Waiting for other threads to finish...        3642s
Waiting for other threads to finish...        3705s
Waiting for other threads to finish...        3769s
Waiting for other threads to finish...        3833s
Waiting for other threads to finish...        3897s
Waiting for other threads to finish...        3961s
Waiting for other threads to finish...        4025s
Waiting for other threads to finish...        4089s
Waiting for other threads to finish...        5429s
Waiting for other threads to finish...        5492s
Concurrent spin time: 2398.41s (can be avoided by choosing Method=3)

Solved with barrier
 4383819    3.1695175e+07   0.000000e+00   0.000000e+00   5554s

Root relaxation: objective 3.169517e+07, 4383819 iterations, 5231.77 seconds (3666.34 work units)

Official comment

Simranjit Kaur

Gurobi Staff

November 13, 2026 01:21

This post is more than two years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum, or try Gurobot, our chatbot interface offering instant, expert-level support.

Jaromił Najman

August 26, 2024 08:44

Hi Krzysztof,

Is it possible that this run is hitting your machine's memory limit? It is possible that the OS starts swapping memory to not abort the process which as a result slows down the affected process tremendously.

If it is a memory issue, you might want to have a look at How do I avoid an out-of-memory condition?

Best regards,
Jaromił

Jonasz Staszek

Community Moderator

August 30, 2024 12:10

I would also add, to what Jaromił wrote, that your model is extremely large. I would suggest you reconsider the formulation of your model.

Judging by the other questions you asked, I believe you are trying to solve an inventory optimization problem. Perhaps this paper could serve as an inspiration.

Best regards
Jonasz

How to debug frozen solver?

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