[sql] Disable memory-mapping under sql::Recovery.

sql/connection.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sql/connection.h"
 
 #include <string.h>
 
 #include "base/bind.h"
 #include "base/debug/dump_without_crashing.h"
@@ skipping 1610 matching lines @@
 
   // http://www.sqlite.org/pragma.html#pragma_journal_mode
   // DELETE (default) - delete -journal file to commit.
   // TRUNCATE - truncate -journal file to commit.
   // PERSIST - zero out header of -journal file to commit.
   // TRUNCATE should be faster than DELETE because it won't need directory
   // changes for each transaction.  PERSIST may break the spirit of using
   // secure_delete.
   ignore_result(Execute("PRAGMA journal_mode = TRUNCATE"));
 
-  // Enable memory-mapped access.  This value will be capped by
-  // SQLITE_MAX_MMAP_SIZE, which could be different between 32-bit and 64-bit
-  // platforms.
-  mmap_enabled_ = false;
-  if (!mmap_disabled_)
-    ignore_result(Execute("PRAGMA mmap_size = 268435456"));  // 256MB.
-  {
-    Statement s(GetUniqueStatement("PRAGMA mmap_size"));
-    if (s.Step() && s.ColumnInt64(0) > 0)
-      mmap_enabled_ = true;
-  }
-
   const base::TimeDelta kBusyTimeout =
     base::TimeDelta::FromSeconds(kBusyTimeoutSeconds);
 
   if (page_size_ != 0) {
     // Enforce SQLite restrictions on |page_size_|.
     DCHECK(!(page_size_ & (page_size_ - 1)))
         << " page_size_ " << page_size_ << " is not a power of two.";
     const int kSqliteMaxPageSize = 32768;  // from sqliteLimit.h
     DCHECK_LE(page_size_, kSqliteMaxPageSize);
     const std::string sql =
         base::StringPrintf("PRAGMA page_size=%d", page_size_);
     ignore_result(ExecuteWithTimeout(sql.c_str(), kBusyTimeout));
   }
 
   if (cache_size_ != 0) {
     const std::string sql =
         base::StringPrintf("PRAGMA cache_size=%d", cache_size_);
     ignore_result(ExecuteWithTimeout(sql.c_str(), kBusyTimeout));
   }
 
   if (!ExecuteWithTimeout("PRAGMA secure_delete=ON", kBusyTimeout)) {
     bool was_poisoned = poisoned_;
     Close();
     if (was_poisoned && retry_flag == RETRY_ON_POISON)
       return OpenInternal(file_name, NO_RETRY);
     return false;
   }
 
+  // Enable memory-mapped access.  The explicit-disable case is because SQLite
+  // can be built to default-enable mmap.  This value will be capped by
+  // SQLITE_MAX_MMAP_SIZE, which could be different between 32-bit and 64-bit
+  // platforms.
+  if (mmap_disabled_) {
+    ignore_result(Execute("PRAGMA mmap_size = 0"));
+  } else {
+    ignore_result(Execute("PRAGMA mmap_size = 268435456"));  // 256MB.
+  }
+
+  // Determine if memory-mapping has actually been enabled.  The Execute() above
+  // can succeed without changing the amount mapped.
+  mmap_enabled_ = false;
+  {
+    Statement s(GetUniqueStatement("PRAGMA mmap_size"));
+    if (s.Step() && s.ColumnInt64(0) > 0)
+      mmap_enabled_ = true;
+  }
+

[Scott Hess - ex-Googler, 2015/11/04 23:36:42]

Hmm, and I moved the stanza down here because it seemed like the thing most
sensitive to database problems should come as late as possible to give other
statements a chance to flush out problems.

   return true;
 }
 
 void Connection::DoRollback() {
   Statement rollback(GetCachedStatement(SQL_FROM_HERE, "ROLLBACK"));
 
   // Collect the rollback time manually, sql::Statement would register it as
   // query time only.
   const base::TimeTicks before = Now();
   rollback.RunWithoutTimers();
@@ skipping 119 matching lines @@
   ignore_result(Execute(kNoWritableSchema));
 
   return ret;
 }
 
 base::TimeTicks TimeSource::Now() {
   return base::TimeTicks::Now();
 }
 
 }  // namespace sql