Simplify cache write

The previous cache write routine was too complex.  I'm sure I can
rewrite it to more elegantly.  But the primary motivation of this
complex logic is for disk activity reduction on Windows 7, and I
observed it on my old IDE disk.  I checked it again recently, and
there is no difference between with and without this complex logic.
For this reason, it was removed.  Will revert this change if many of
users are not happy with this.

src/AbstractSingleDiskAdaptor.cc

@@ -96,49 +96,10 @@ ssize_t AbstractSingleDiskAdaptor::readDataDropCache(unsigned char* data,
 
 void AbstractSingleDiskAdaptor::writeCache(const WrDiskCacheEntry* entry)
 {
-  // Write cached data in 4KiB aligned offset. This reduces disk
-  // activity especially on Windows 7 NTFS. In this code, we assume
-  // that maximum length of DataCell data is 16KiB to simplify the
-  // code.
-  unsigned char buf[16_k];
-  int64_t start = 0;
-  size_t buflen = 0;
-  size_t buffoffset = 0;
-  const WrDiskCacheEntry::DataCellSet& dataSet = entry->getDataSet();
-  for (auto& d : dataSet) {
-    if (start + static_cast<ssize_t>(buflen) < d->goff) {
-      A2_LOG_DEBUG(fmt("Cache flush goff=%" PRId64 ", len=%lu", start,
-                       static_cast<unsigned long>(buflen)));
-      writeData(buf + buffoffset, buflen - buffoffset, start);
-      start = d->goff;
-      buflen = buffoffset = 0;
-    }
-    if (buflen == 0 && (d->goff & 0xfff) == 0 && (d->len & 0xfff) == 0) {
-      // Already aligned. Write it without copy.
-      A2_LOG_DEBUG(fmt("Cache flush goff=%" PRId64 ", len=%lu", start,
-                       static_cast<unsigned long>(d->len)));
-      writeData(d->data + d->offset, d->len, start);
-      start += d->len;
-    }
-    else {
-      if (buflen == 0) {
-        buflen = buffoffset = d->goff & 0xfff;
-      }
-      size_t wlen = std::min(sizeof(buf) - buflen, d->len);
-      memcpy(buf + buflen, d->data + d->offset, wlen);
-      buflen += wlen;
-      if (buflen == sizeof(buf)) {
-        A2_LOG_DEBUG(fmt("Cache flush goff=%" PRId64 ", len=%lu", start,
-                         static_cast<unsigned long>(buflen)));
-        writeData(buf + buffoffset, buflen - buffoffset, start);
-        memcpy(buf, d->data + d->offset + wlen, d->len - wlen);
-        start += sizeof(buf) - buffoffset;
-        buflen = d->len - wlen;
-        buffoffset = 0;
-      }
-    }
+  for (auto& d : entry->getDataSet()) {
+    A2_LOG_DEBUG(fmt("Cache flush goff=%" PRId64 ", len=%lu", d->goff, d->len));
+    writeData(d->data + d->offset, d->len, d->goff);
   }
-  writeData(buf + buffoffset, buflen - buffoffset, start);
 }
 
 bool AbstractSingleDiskAdaptor::fileExists()

src/MultiDiskAdaptor.cc

@@ -412,98 +412,10 @@ ssize_t MultiDiskAdaptor::readData(unsigned char* data, size_t len,
 
 void MultiDiskAdaptor::writeCache(const WrDiskCacheEntry* entry)
 {
-  // Write cached data in 4KiB aligned offset. This reduces disk
-  // activity especially on Windows 7 NTFS.
-  unsigned char buf[16_k];
-  size_t buflen = 0;
-  size_t buffoffset = 0;
-  auto& dataSet = entry->getDataSet();
-  if (dataSet.empty()) {
-    return;
-  }
-  auto dent =
-      findFirstDiskWriterEntry(diskWriterEntries_, (*dataSet.begin())->goff),
-       eod = diskWriterEntries_.cend();
-  auto i = std::begin(dataSet), eoi = std::end(dataSet);
-  size_t celloff = 0;
-  for (; dent != eod; ++dent) {
-    int64_t lstart = 0, lp = 0;
-    auto& fent = (*dent)->getFileEntry();
-    if (fent->getLength() == 0) {
-      continue;
-    }
-    for (; i != eoi;) {
-      if (std::max(fent->getOffset(),
-                   static_cast<int64_t>((*i)->goff + celloff)) <
-          std::min(fent->getLastOffset(),
-                   static_cast<int64_t>((*i)->goff + (*i)->len))) {
-        openIfNot((*dent).get(), &DiskWriterEntry::openFile);
-        if (!(*dent)->isOpen()) {
-          throwOnDiskWriterNotOpened((*dent).get(), (*i)->goff + celloff);
-        }
-      }
-      else {
-        A2_LOG_DEBUG(fmt("%s Cache flush loff=%" PRId64 ", len=%lu",
-                         fent->getPath().c_str(), lstart,
-                         static_cast<unsigned long>(buflen - buffoffset)));
-        (*dent)->getDiskWriter()->writeData(buf + buffoffset,
-                                            buflen - buffoffset, lstart);
-        buflen = buffoffset = 0;
-        break;
-      }
-      int64_t loff = fent->gtoloff((*i)->goff + celloff);
-      if (static_cast<int64_t>(lstart + buflen) < loff) {
-        A2_LOG_DEBUG(fmt("%s Cache flush loff=%" PRId64 ", len=%lu",
-                         fent->getPath().c_str(), lstart,
-                         static_cast<unsigned long>(buflen - buffoffset)));
-        (*dent)->getDiskWriter()->writeData(buf + buffoffset,
-                                            buflen - buffoffset, lstart);
-        lstart = lp = loff;
-        buflen = buffoffset = 0;
-      }
-      // If the position of the cache data is not aligned, offset
-      // buffer so that next write can be aligned.
-      if (buflen == 0) {
-        buflen = buffoffset = loff & 0xfff;
-      }
-      assert((*i)->len > celloff);
-      for (;;) {
-        size_t wlen = std::min(static_cast<int64_t>((*i)->len - celloff),
-                               fent->getLength() - lp);
-        wlen = std::min(wlen, sizeof(buf) - buflen);
-        memcpy(buf + buflen, (*i)->data + (*i)->offset + celloff, wlen);
-        buflen += wlen;
-        celloff += wlen;
-        lp += wlen;
-        if (lp == fent->getLength() || buflen == sizeof(buf)) {
-          A2_LOG_DEBUG(fmt("%s Cache flush loff=%" PRId64 ", len=%lu",
-                           fent->getPath().c_str(), lstart,
-                           static_cast<unsigned long>(buflen - buffoffset)));
-          (*dent)->getDiskWriter()->writeData(buf + buffoffset,
-                                              buflen - buffoffset, lstart);
-          lstart += buflen - buffoffset;
-          lp = lstart;
-          buflen = buffoffset = 0;
-        }
-        if (lp == fent->getLength() || celloff == (*i)->len) {
-          break;
-        }
-      }
-      if (celloff == (*i)->len) {
-        ++i;
-        celloff = 0;
-      }
-    }
-    if (i == eoi) {
-      A2_LOG_DEBUG(fmt("%s Cache flush loff=%" PRId64 ", len=%lu",
-                       fent->getPath().c_str(), lstart,
-                       static_cast<unsigned long>(buflen - buffoffset)));
-      (*dent)->getDiskWriter()->writeData(buf + buffoffset, buflen - buffoffset,
-                                          lstart);
-      break;
-    }
+  for (auto& d : entry->getDataSet()) {
+    A2_LOG_DEBUG(fmt("Cache flush goff=%" PRId64 ", len=%lu", d->goff, d->len));
+    writeData(d->data + d->offset, d->len, d->goff);
   }
-  assert(i == eoi);
 }
 
 bool MultiDiskAdaptor::fileExists()