Create a transaction:
To explicitly roll back a transaction, such as from a conditional code block, you can call the failure method, and the transaction will be unconditionally rolled back at the end of the block. Neither calling the success method nor calling the failure method will cause the transaction to be rolled back (default).
Define the name of the USER tag as a schema indexable property in a transaction, and then actually set a real user's value using a separate transaction:
Many database management systems use a lock mechanism to manage simultaneous access to the same database. Neo4j transactions control each graphical database resource (nodes and relationships) with clear read and write locks.
Multiple read locks are not mutually exclusive, and multiple locks can be obtained in the same data resource in multiple threads at the same time. At a given moment, only one write lock can be obtained for the same data resource, and there must be no other active locks, either read locks or write locks.
The default setting for Neo4j transactions does not automatically acquire read locks. Therefore, the data read is the state of the latest commit of the node, relationship, and index entity, unless the local modification (even if not committed) is visible in its own transaction.
Write locks are automatically obtained when an attempt is made to make a change to any graphics resource and are valid for the duration of the transaction. Each transaction ensures that all locks are automatically released upon completion.
If a higher level of isolation is needed to ensure that others can't modify the graphics resource being read, Neo4j provides a potentially explicit read lock on the graphics resource. The corresponding code is given in Listing 7-5, but this time there is an additional explicit request to get a read lock on the node before reading any properties.
There are two good reasons to avoid using system locks when reading data. As mentioned before, this will first result in the state of the transaction and is very memory intensive. Second, the main trade-off here is to write data at the same time, because the thread wants to update any node or relationship that has an explicit read lock, which is locked before the lock is released or the transaction is completed.
If transaction A attempts to lock them in the order of node 1 and node 2, and transaction B attempts to acquire locks in the reverse order for the same node, then each transaction may lock one node and wait indefinitely for the other node to release, thus Generate an invalid lock.
When an invalid lock occurs, Neo4j has a built-in mechanism to detect it, and if so, throws a DeadlockDetectedExcepTIon exception and the transaction is rolled back. The detection of invalid locks can only be done when the lock is specifically managed by Neo4j, which means by relying on Neo4j's automatic default locking mechanism, or simply by using the related locking methods (acquireReadLock and acquireWriteLock) of the Neo4j API we discussed earlier. If you use any other locking mechanism, such as using Java's synchronized keywords, even if an invalid lock occurs, it will not be detected, and the application is likely to terminate.
To effectively handle invalid locks: The first one insists on using the core API provided by Neo4j without using any external locking mechanism. This will ensure that Neo4j's invalid lock detection mechanism is effective, ensuring that your application is not fully locked and that the data is consistent. All operations in the Neo4j core API (unless otherwise specified) are thread-safe, so external synchronization is generally not required. The other is to avoid invalid locks by ensuring that graphical resources can be accessed in the same order.
Deep traversal1 traversal order
Each time the visitor accesses a node, it needs to decide which node to access next node along the next step, repeating the process until the end of the traversal. By selecting an appropriate path in the graph, the traversal can end very quickly and use very little memory. This is the two main sequential algorithms in graph theory, and these two algorithms are used in most Neo4j traversals: depth-first algorithms and breadth-first algorithms.
Depth first:
Depth-first order indicates that you should first jump to the first-level child of the node that you are currently in and that you have not previously visited. If all of the next generation of child nodes have been accessed, they should be returned to the first node with child nodes that have not been visited.
Use Neo4j to traverse the API depth-first traversal of the entire graph:
Depth first is the default branch order strategy of Neo4j. When creating a traversal description, if you do not specify the order of traversal, the default is depth first.
The composite terminal is a typical representative of the connector (CONNECTOR), which is composed of a plug (female) and a socket (male) to realize the connection function. For the transfer of voltage, current and signal, this series is characterized by safe, reliable and stable contact, and is mainly used in electric power, communication, industrial control and other industries.
composite terminal block,component terminal block,composite terminal block adapter
Sichuan Xinlian electronic science and technology Company , https://www.sztmlch.com