Summary:
A temporary hack to work around a bug in 6.10, 6.11, 6.12, 6.13 and
6.14. The bug will write out 8 bytes to OPTIONS file from the starting
address of BlockBasedTableOptions.read_amp_bytes_per_bit which is
actually a uint32. Consequently, the value of read_amp_bytes_per_bit
written in the OPTIONS file is wrong. From 6.15, RocksDB will
try to parse the read_amp_bytes_per_bit from OPTIONS file as a uint32.
To be able to load OPTIONS file generated by affected releases before
the fix, we need to manually parse read_amp_bytes_per_bit with this hack.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/7659
Test Plan:
Generate a db with current 6.14.fb (head at b6db05dbb5). Maybe use db_stress.
Checkout this PR, run
```
~/rocksdb/ldb --db=. --try_load_options --ignore_unknown_options idump --count_only
```
Expect success, and should not see
```
Failed: Invalid argument: Error parsing read_amp_bytes_per_bit:17179869184
```
Also
make check
Reviewed By: anand1976
Differential Revision: D24954752
Pulled By: riversand963
fbshipit-source-id: c7b802fc3e52acd050a4fc1cd475016122234394
98174bc3a3