Look into making mmapdirectory's unmap safer [LUCENE-7409] #8462
Description
I have seen a few bugs around this recently: of course its a bug in application code but a JVM crash is not good.
I think we should see if we can prevent the crashes better than the current weak map, e.g. make it a safer option.
I made an ugly prototype here: https://github.com/apache/lucene-solr/compare/master...rmuir:ace?expand=1
It has a test that crashes the JVM without the patch but passes with.
Hacky patch only implements readBytes() but has no problems with the luceneutil benchmark (1M):
Report after iter 19:
Task QPS base StdDev QPS patch StdDev Pct diff
IntNRQ 105.23 (17.6%) 100.42 (10.1%) -4.6% ( -27% - 28%)
Respell 128.35 (13.2%) 125.88 (7.4%) -1.9% ( -19% - 21%)
Fuzzy1 110.14 (17.2%) 108.28 (13.2%) -1.7% ( -27% - 34%)
LowPhrase 337.02 (13.0%) 333.72 (9.3%) -1.0% ( -20% - 24%)
MedPhrase 146.44 (12.9%) 145.55 (8.0%) -0.6% ( -19% - 23%)
MedSpanNear 96.85 (13.1%) 96.57 (7.8%) -0.3% ( -18% - 23%)
HighSpanNear 95.85 (13.9%) 96.33 (8.2%) 0.5% ( -18% - 26%)
HighPhrase 146.84 (13.6%) 148.40 (8.4%) 1.1% ( -18% - 26%)
HighTerm 295.15 (15.8%) 298.77 (9.5%) 1.2% ( -20% - 31%)
LowSpanNear 268.80 (12.4%) 272.16 (7.9%) 1.2% ( -16% - 24%)
Wildcard 284.09 (11.7%) 290.91 (8.9%) 2.4% ( -16% - 25%)
Prefix3 212.50 (15.4%) 217.76 (10.0%) 2.5% ( -19% - 32%)
OrHighLow 358.65 (15.0%) 368.93 (10.7%) 2.9% ( -19% - 33%)
AndHighMed 799.65 (13.2%) 834.74 (7.8%) 4.4% ( -14% - 29%)
MedSloppyPhrase 229.36 (15.9%) 239.95 (9.8%) 4.6% ( -18% - 36%)
Fuzzy2 69.58 (14.6%) 72.82 (14.5%) 4.7% ( -21% - 39%)
AndHighHigh 426.98 (12.8%) 451.77 (7.3%) 5.8% ( -12% - 29%)
MedTerm 1361.11 (14.5%) 1450.90 (9.2%) 6.6% ( -14% - 35%)
PKLookup 266.61 (13.4%) 284.28 (8.4%) 6.6% ( -13% - 32%)
HighSloppyPhrase 251.22 (16.9%) 268.32 (10.7%) 6.8% ( -17% - 41%)
OrHighMed 235.92 (17.2%) 253.12 (12.8%) 7.3% ( -19% - 45%)
OrHighHigh 186.79 (13.5%) 201.15 (9.7%) 7.7% ( -13% - 35%)
LowSloppyPhrase 395.23 (15.9%) 425.93 (9.3%) 7.8% ( -15% - 39%)
AndHighLow 1128.28 (14.9%) 1242.11 (8.2%) 10.1% ( -11% - 38%)
LowTerm 3024.62 (12.9%) 3367.65 (9.7%) 11.3% ( -9% - 39%)
We should do more testing. Maybe its totally the wrong tradeoff, maybe we only need handles for getters and everything inlines correctly, rather than needing a ton for every getXYZ() method...
Migrated from LUCENE-7409 by Robert Muir (@rmuir), resolved Aug 18 2016
Attachments: LUCENE-7409.patch, StoreStore.java
Linked issues: