update类型的数据无法更新到目标库，通过追踪源码，发现同步源库的binlog日志中UPDATE类型的old参数为null,导致跳出更新程序，无法更新。

仔细检查了目标库的binlog是否开启，以及binlog的格式设置，以及binlog_row_image的设置，均满足官方要求。通过换服务器安装，换目标库等等的尝试发现都无果之后，走上了修改源码的道路。这里定位问题所在为源库MySQL的未知设置问题。

修改com.alibaba.otter.canal.client.adapter.rdb.service.RdbSyncService类中的update方法如下。
第一种方式对binlog中的old参数值不进行判断，直接对所有字段值进行update操作；
第二种方式兼容原有逻辑，如果有old参数值按照原有逻辑进行，如果没有按照上述第一种方式进行；

第一种方式

        /**
         * 更新操作
         *
         * @param config 配置项
         * @param dml DML数据
         */
        private void update(BatchExecutor batchExecutor, MappingConfig config, SingleDml dml) throws SQLException {
            Map<String, Object> data = dml.getData();
            if (data == null || data.isEmpty()) {
                return;
            }
            //这里先设置了插入，根据需求，可以自行选择是否需要。
            insert(batchExecutor,config,dml);
    //将old的判断去除。
    //        Map<String, Object> old = dml.getOld();
    //        if (old == null || old.isEmpty()) {
    //            return;
    //        }
    //将下方的old调整为传过来的data.核心思想就是根据data解析字段为目标字段，并对目标库中的所有字段进行更新。
            DbMapping dbMapping = config.getDbMapping();
    
            Map<String, String> columnsMap = SyncUtil.getColumnsMap(dbMapping, data);
    
            Map<String, Integer> ctype = getTargetColumnType(batchExecutor.getConn(), config);
    
            StringBuilder updateSql = new StringBuilder();
            updateSql.append("UPDATE ").append(SyncUtil.getDbTableName(dbMapping)).append(" SET ");
    //        Set<String> columnsSet = data.keySet();
            List<Map<String, ?>> values = new ArrayList<>();
            boolean hasMatched = false;
    //        for (String srcColumnName : old.keySet()) {
            for (String srcColumnName : data.keySet()) {
                List<String> targetColumnNames = new ArrayList<>();
                columnsMap.forEach((targetColumn, srcColumn) -> {
                    if (srcColumnName.equalsIgnoreCase(srcColumn)) {
                        targetColumnNames.add(targetColumn);
                    }
                });
                if (!targetColumnNames.isEmpty()) {
                    hasMatched = true;
                    for (String targetColumnName : targetColumnNames) {
                        updateSql.append("`").append(targetColumnName).append("`").append("=?, ");
                        Integer type = ctype.get(Util.cleanColumn(targetColumnName).toLowerCase());
                        if (type == null) {
                            throw new RuntimeException("Target column: " + targetColumnName + " not matched");
                        }
                        BatchExecutor.setValue(values, type, data.get(srcColumnName));
                    }
                }
            }
            if (!hasMatched) {
                logger.warn("Did not matched any columns to update ");
                return;
            }
            int len = updateSql.length();
            updateSql.delete(len - 2, len).append(" WHERE ");
    
            // 拼接主键
    //        appendCondition(dbMapping, updateSql, ctype, values, data, old);
            appendCondition(dbMapping, updateSql, ctype, values, data, data);
            batchExecutor.execute(updateSql.toString(), values);
            if (logger.isTraceEnabled()) {
                logger.trace("Update target table, sql: {}", updateSql);
            }
        }
    

第二种方式

  /**
     * 更新操作
     *
     * @param config 配置项
     * @param dml DML数据
     */
    private void update(BatchExecutor batchExecutor, MappingConfig config, SingleDml dml) throws SQLException {
        Map<String, Object> data = dml.getData();
        if (data == null || data.isEmpty()) {
            return;
        }
//这里用common作为公共变量存储data或者old
        Map<String, Object> common = new ConcurrentHashMap<String, Object>();
        Map<String, Object> old = dml.getOld();
        if (old == null || old.isEmpty()) {
            common = data;
        }else{
            common = old;
        }

        DbMapping dbMapping = config.getDbMapping();

        Map<String, String> columnsMap = SyncUtil.getColumnsMap(dbMapping, data);

        Map<String, Integer> ctype = getTargetColumnType(batchExecutor.getConn(), config);

        StringBuilder updateSql = new StringBuilder();
        updateSql.append("UPDATE ").append(SyncUtil.getDbTableName(dbMapping)).append(" SET ");
        List<Map<String, ?>> values = new ArrayList<>();
        boolean hasMatched = false;
//        for (String srcColumnName : old.keySet()) {
        for (String srcColumnName : common.keySet()) {
            List<String> targetColumnNames = new ArrayList<>();
            columnsMap.forEach((targetColumn, srcColumn) -> {
                if (srcColumnName.equalsIgnoreCase(srcColumn)) {
                    targetColumnNames.add(targetColumn);
                }
            });
            if (!targetColumnNames.isEmpty()) {
                hasMatched = true;
                for (String targetColumnName : targetColumnNames) {
                    updateSql.append("`").append(targetColumnName).append("`").append("=?, ");
                    Integer type = ctype.get(Util.cleanColumn(targetColumnName).toLowerCase());
                    if (type == null) {
                        throw new RuntimeException("Target column: " + targetColumnName + " not matched");
                    }
                    BatchExecutor.setValue(values, type, data.get(srcColumnName));
                }
            }
        }
        if (!hasMatched) {
            logger.warn("Did not matched any columns to update ");
            return;
        int len = updateSql.length();
        updateSql.delete(len - 2, len).append(" WHERE ");

        // 拼接主键
//        appendCondition(dbMapping, updateSql, ctype, values, data, old);
        appendCondition(dbMapping, updateSql, ctype, values, data, common);
        batchExecutor.execute(updateSql.toString(), values);
        if (logger.isTraceEnabled()) {
            logger.trace("Update target table, sql: {}", updateSql);
        }
    }