Merge "Flush after every 2MB merge of replace ops." am: 8f7aaf9d am: 93340462

}

bool Worker::MergeReplaceZeroOps() {

    // Flush every 8192 ops. Since all ops are independent and there is no

    // Flush after merging 2MB. Since all ops are independent and there is no

    // dependency between COW ops, we will flush the data and the number

    // of ops merged in COW file for every 8192 ops. If there is a crash,

    // we will end up replaying some of the COW ops which were already merged.

    // That is ok.

    // of ops merged in COW block device. If there is a crash, we will

    // end up replaying some of the COW ops which were already merged. That is

    // ok.

    //

    // Why 8192 ops ? Increasing this may improve merge time 3-4 seconds but

    // we need to make sure that we checkpoint; 8k ops seems optimal. In-case

    // if there is a crash merge should always make forward progress.

    int total_ops_merged_per_commit = (PAYLOAD_BUFFER_SZ / BLOCK_SZ) * 32;

    // Although increasing this greater than 2MB may help in improving merge

    // times; however, on devices with low memory, this can be problematic

    // when there are multiple merge threads in parallel.

    int total_ops_merged_per_commit = (PAYLOAD_BUFFER_SZ / BLOCK_SZ) * 2;

    int num_ops_merged = 0;

    SNAP_LOG(INFO) << "MergeReplaceZeroOps started....";