[RocksDB] Introduce an option to skip log error on recovery

Summary:
Currently, with paranoid_check on, DB::Open will fail on any log read error on recovery.
If client is ok with losing most recent updates, we could simply skip those errors.
However, it's important to introduce an additional flag, so that paranoid_check can
still guard against more serious problems.

Test Plan: make check; db_stress

Reviewers: dhruba, emayanke

Reviewed By: emayanke

CC: leveldb, emayanke

Differential Revision: https://reviews.facebook.net/D10869

db/db_impl.cc

@@ -590,7 +590,8 @@ Status DBImpl::RecoverLogFile(uint64_t log_number,
     Env* env;
     Logger* info_log;
     const char* fname;
-    Status* status;  // nullptr if options_.paranoid_checks==false
+    Status* status;  // nullptr if options_.paranoid_checks==false or
+                     //            options_.skip_log_error_on_recovery==true
     virtual void Corruption(size_t bytes, const Status& s) {
       Log(info_log, "%s%s: dropping %d bytes; %s",
           (this->status == nullptr ? "(ignoring error) " : ""),
@@ -615,7 +616,8 @@ Status DBImpl::RecoverLogFile(uint64_t log_number,
   reporter.env = env_;
   reporter.info_log = options_.info_log.get();
   reporter.fname = fname.c_str();
-  reporter.status = (options_.paranoid_checks ? &status : nullptr);
+  reporter.status = (options_.paranoid_checks &&
+                     !options_.skip_log_error_on_recovery ? &status : nullptr);
   // We intentially make log::Reader do checksumming even if
   // paranoid_checks==false so that corruptions cause entire commits
   // to be skipped instead of propagating bad information (like overly
@@ -633,8 +635,7 @@ Status DBImpl::RecoverLogFile(uint64_t log_number,
   if (external_table) {
     mem = external_table;
   }
-  while (reader.ReadRecord(&record, &scratch) &&
-         status.ok()) {
+  while (reader.ReadRecord(&record, &scratch) && status.ok()) {
     if (record.size() < 12) {
       reporter.Corruption(
           record.size(), Status::Corruption("log record too small"));

include/leveldb/options.h

@@ -424,6 +424,12 @@ struct Options {
 
   // Disable child process inherit open files. Default: true
   bool is_fd_close_on_exec;
+
+  // Skip log corruption error on recovery (If client is ok with
+  // losing most recent changes)
+  // Default: false
+  bool skip_log_error_on_recovery;
+
 };
 
 // Options that control read operations

util/options.cc

@@ -68,7 +68,8 @@ Options::Options()
       allow_readahead_compactions(true),
       allow_mmap_reads(false),
       allow_mmap_writes(true),
-      is_fd_close_on_exec(true) {
+      is_fd_close_on_exec(true),
+      skip_log_error_on_recovery(false) {
 }
 
 void
@@ -189,6 +190,8 @@ Options::Dump(Logger* log) const
         allow_mmap_writes);
     Log(log,"                     Options.is_fd_close_on_exec: %d",
         is_fd_close_on_exec);
+    Log(log,"              Options.skip_log_error_on_recovery: %d",
+        skip_log_error_on_recovery);
 }   // Options::Dump
 
 //