openfire(4)数据库浅析之序列

openfire中提供了生产序列的管理器（SequenceManager），其构造函数如下：

 

public SequenceManager(int seqType, int size) {
        managers.put(seqType, this);
        this.type = seqType;
        this.blockSize = size;
        currentID = 0l;
        maxID = 0l;
    }

seqType，为序列类型，默认有3种类型：

    public static final int ROSTER = 18;
    public static final int OFFLINE = 19;
    public static final int MUC_ROOM = 23;

 

size：序列的增加值。例如a=a+2；

 

 

private void getNextBlock(int count) {
        if (count == 0) {
            Log.error("Failed at last attempt to obtain an ID, aborting...");
            return;
        }

        Connection con = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        boolean abortTransaction = false;
        boolean success = false;

        try {
            con = DbConnectionManager.getTransactionConnection();
            // Get the current ID from the database.
            pstmt = con.prepareStatement(LOAD_ID);
            pstmt.setInt(1, type);
            rs = pstmt.executeQuery();

            long currentID = 1;
            if (rs.next()) {
                currentID = rs.getLong(1);
            }
            else {
                createNewID(con, type);
            }
            DbConnectionManager.fastcloseStmt(rs, pstmt);

            // Increment the id to define our block.
            long newID = currentID + blockSize;
            // The WHERE clause includes the last value of the id. This ensures
            // that an update will occur only if nobody else has performed an
            // update first.
            pstmt = con.prepareStatement(UPDATE_ID);
            pstmt.setLong(1, newID);
            pstmt.setInt(2, type);
            pstmt.setLong(3, currentID);
            // Check to see if the row was affected. If not, some other process
            // already changed the original id that we read. Therefore, this
            // round failed and we'll have to try again.
            success = pstmt.executeUpdate() == 1;
            if (success) {
                this.currentID = currentID;
                this.maxID = newID;
            }
        }
        catch (SQLException e) {
            Log.error(e.getMessage(), e);
            abortTransaction = true;
        }
        finally {
            DbConnectionManager.closeStatement(rs, pstmt);
            DbConnectionManager.closeTransactionConnection(con, abortTransaction);
        }

        if (!success) {
            Log.error("WARNING: failed to obtain next ID block due to " +
                    "thread contention. Trying again...");
            // Call this method again, but sleep briefly to try to avoid thread contention.
            try {
                Thread.sleep(75);
            }
            catch (InterruptedException ie) {
                // Ignore.
            }
            getNextBlock(count - 1);
        }
    }

此方法为：更具类型到数据库中ofid查询ID，获取表中的id，然后id加一个变量，然后将新的id更新到数据库中。

 

private void createNewID(Connection con, int type) throws SQLException {
        Log.warn("Autocreating jiveID row for type '" + type + "'");

        // create new ID row
        PreparedStatement pstmt = null;

        try {
            pstmt = con.prepareStatement(CREATE_ID);
            pstmt.setInt(1, type);
            pstmt.execute();
        }
        finally {
            DbConnectionManager.closeStatement(pstmt);
        }
    }

在表中创建一条序列的记录。

 

此篇文章就到此，稍后会有更多关于openfire的个人解读。

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