// Convert an index iterator value (i.e., an encoded BlockHandle)
// into an iterator over the contents of the corresponding block.
Iterator* Table::BlockReader(void* arg,
const ReadOptions& options,
const Slice& index_value) {
Table* table = reinterpret_cast<Table*>(arg);
Cache* block_cache = table->rep_->options.block_cache;
Block* block = NULL;
Cache::Handle* cache_handle = NULL;
BlockHandle handle;
Slice input = index_value;
Status s = handle.DecodeFrom(&input);
// We intentionally allow extra stuff in index_value so that we
// can add more features in the future.
if (s.ok()) {
BlockContents contents;
if (block_cache != NULL) {
char cache_key_buffer[16];
EncodeFixed64(cache_key_buffer, table->rep_->cache_id);
EncodeFixed64(cache_key_buffer+8, handle.offset());
Slice key(cache_key_buffer, sizeof(cache_key_buffer));
cache_handle = block_cache->Lookup(key);
if (cache_handle != NULL) {
block = reinterpret_cast<Block*>(block_cache->Value(cache_handle));
} else {
s = ReadBlock(table->rep_->file, options, handle, &contents);
if (s.ok()) {
block = new Block(contents);
if (contents.cachable && options.fill_cache) {
cache_handle = block_cache->Insert(
key, block, block->size(), &DeleteCachedBlock);
}
}
}
} else {
s = ReadBlock(table->rep_->file, options, handle, &contents);
if (s.ok()) {
block = new Block(contents);
}
}
}
Iterator* iter;
if (block != NULL) {
iter = block->NewIterator(table->rep_->options.comparator);
if (cache_handle == NULL) {
iter->RegisterCleanup(&DeleteBlock, block, NULL);
} else {
iter->RegisterCleanup(&ReleaseBlock, block_cache, cache_handle);
}
} else {
iter = NewErrorIterator(s);
}
return iter;
}
