cloud/src/meta-service/doris_txn.cpp

// Licensed to the Apache Software Foundation (ASF) under one
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// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
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// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

#include "doris_txn.h"

#include <bit>

namespace doris::cloud {

int get_txn_id_from_fdb_ts(std::string_view fdb_vts, int64_t* txn_id) {
    if (fdb_vts.size() != 10) return 1; // Malformed version timestamp

    // fdb version timestamp is big-endian
    //           MSB               LSB
    //           0000000000000000 0000
    //           ts               seq
    // byte addr 0 1 2 3 4 5 6 7  8 9
    int64_t ver = *reinterpret_cast<const int64_t*>(fdb_vts.data());

    // TODO(gavin): implementation for big-endian or make it endian-independent
    static_assert(std::endian::native == std::endian::little); // Since c++20
    // Convert big endian to little endian
    static auto to_little = [](int64_t v) {
        v = ((v & 0xffffffff00000000) >> 32) | ((v & 0x00000000ffffffff) << 32);
        v = ((v & 0xffff0000ffff0000) >> 16) | ((v & 0x0000ffff0000ffff) << 16);
        v = ((v & 0xff00ff00ff00ff00) >> 8) | ((v & 0x00ff00ff00ff00ff) << 8);
        return v;
    };
    ver = to_little(ver);

    int64_t seq = *reinterpret_cast<const int64_t*>(fdb_vts.data() + 2);
    seq = to_little(seq);
    seq &= 0x000000000000ffff; // Strip off non-seq part

    // CAUTION: DO NOT EVER TOUCH IT!!! UNLESS YOU ARE PREPARED FOR THE DOOM!!!
    // CAUTION: DO NOT EVER TOUCH IT!!! UNLESS YOU ARE PREPARED FOR THE DOOM!!!
    // CAUTION: DO NOT EVER TOUCH IT!!! UNLESS YOU ARE PREPARED FOR THE DOOM!!!
    static constexpr int SEQ_RETAIN_BITS = 10;

    if (seq >= (1L << SEQ_RETAIN_BITS)) {
        // seq exceeds the max value
        return 2;
    }

    // Squeeze seq into ver
    seq &= ((1L << SEQ_RETAIN_BITS) - 1L); // Strip off uninterested part
    ver <<= SEQ_RETAIN_BITS;
    ver |= seq;

    *txn_id = ver;
    return 0;
}

} // namespace doris::cloud