pecl:mysqlnd_ms

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pecl:mysqlnd_ms [2012/04/16 13:26] – [Raw Bin ideas (RFCs)] uwpecl:mysqlnd_ms [2012/04/17 12:06] – [Development steps (release planning)] uw
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   * [open] More fail over options   * [open] More fail over options
     * [open] Silent and automatic connection fail over if server returns configured error code     * [open] Silent and automatic connection fail over if server returns configured error code
 +      * NOTE: this may require refactoring of four filters. 
     * [open] Automatic on-connect fail over, if activated, shall be done in a loop until a connection can be opened. Currently we stop after the first attempt. If automatic fail over is on, we try "next" and in case of a failure of "next" we stop. With the new logic there shall be no stop until all possible "next" have been tried.     * [open] Automatic on-connect fail over, if activated, shall be done in a loop until a connection can be opened. Currently we stop after the first attempt. If automatic fail over is on, we try "next" and in case of a failure of "next" we stop. With the new logic there shall be no stop until all possible "next" have been tried.
 +    * [open] Remember failed hosts for the duration of a web request (the plugins' typical lifespan)
  
   * [open] Support directing statements manually to a group of nodes for more efficient server cache usage   * [open] Support directing statements manually to a group of nodes for more efficient server cache usage
   * [open] Refine QoS session consistency server selection policy   * [open] Refine QoS session consistency server selection policy
     * [open] Support "wait for GTID". Currently we loop over all servers until we find a matching one. MySQL 5.6 allows SQL users either to fetch the latest GTID or SQL users can ask for a GTID and their request will block until the GTID has been replicated on the server. We should support the latter logic as well.     * [open] Support "wait for GTID". Currently we loop over all servers until we find a matching one. MySQL 5.6 allows SQL users either to fetch the latest GTID or SQL users can ask for a GTID and their request will block until the GTID has been replicated on the server. We should support the latter logic as well.
 +    * [open] Remember the most current server and test this one first when searching for a GTID (a synchronous server). Use of cached information is possible for the duration of a read-only request sequence. The cache must be flushed and refreshed for every write.
  
   * [open] Improve load balancing   * [open] Improve load balancing
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 == Problem to solve / Idea == == Problem to solve / Idea ==
  
-MySQL replication is asnychronous. Slaves are //eventual consistent// because there is a time lag between an update on the master and the ability of all clients to read that update from the slaves. Slaves may serve stale data.+MySQL replication is asynchronous. Slaves are //eventual consistent// because there is a time lag between an update on the master and the ability of all clients to read that update from the slaves. Slaves may serve stale data.
  
 MySQL replication used for read scale-out requires applications to be able to cope with stale data. If stale data is acceptable, a replication system may replace a MySQL slave read access with an access to a local, eventually stale, cache. **The cache access will lower network latency resulting in faster reply to the query. Furthermore, it will reduce the load on the MySQL replication slaves, thus requiring less machines for a given read workload.** MySQL replication used for read scale-out requires applications to be able to cope with stale data. If stale data is acceptable, a replication system may replace a MySQL slave read access with an access to a local, eventually stale, cache. **The cache access will lower network latency resulting in faster reply to the query. Furthermore, it will reduce the load on the MySQL replication slaves, thus requiring less machines for a given read workload.**
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 Furthermore, it shall be possible to link the automatic fail over to certain error codes: if A returns error n, try next. If A returns m, stop the search and bail out. This way we can differentiate between a server that rejects new requests, e.g. because its overloaded, and a server that has failed. Furthermore, it shall be possible to link the automatic fail over to certain error codes: if A returns error n, try next. If A returns m, stop the search and bail out. This way we can differentiate between a server that rejects new requests, e.g. because its overloaded, and a server that has failed.
  
 +=== Support directing statements manually to a group of nodes for more efficient server cache usage ===
  
 +== Problem to solve / Idea ==
 +
 +In large clusters users can improve performance by optimizing query distribution and server selection using criteria such as cache usage, distance or latency. Application developers shall be allowed to annotate a statement in a way that its executed on a certain group of nodes. 
 +
 +Server cache usage can be optimized by distributing queries in a way that they hit hot caches. For example, clients may want to run all accesses to table A, B and C on the node group 1 and table accesses to D preferably on group 2. Because we do not support automatic table filtering/partitioning clients shall be allowed to manually route requests to the appropriate groups. 
 +
 +Some nodes may be co-located to clients whereas others may be remote. This is often done in large systems when storing multiple copies, e.g. on the machine, on the rack, in the same data center, in a different data center. In case of MySQL Replication its unlikely to find such highly optimized setups, however, there may be nodes closer to the client than others. Nodes closer to a client may be given a certain alias or group name and application developers shall be allowed to hint routing to a group of such nodes.
 +
 +== Feature description ==
 +
 +For every node in the configuration users shall be able to set one or more group names. A SQL hint, for example, MS_GROUP=name can be used to hint the load balancer to direct a request to a certain node group.
 +
 +
 +=== Refine QoS session consistency server selection policy ===
 +
 +== Problem to solve / Idea ==
 +
 +Users can request session consistency. Session consistency guarantees that a user will only be redirected to nodes that have already replicated his changes. Currently we check the status of all configured nodes before we pick a node for statement execution. Checking the status causes extra load on the nodes.
 +
 +== Feature description ==
 +
 +Two additional ways for finding candidates help lowering the overhead:
 +
 +   * Wait for GTID
 +   * Cache/persist GTID/synchron-status
 +
 +There are two ways to check in MySQL 5.6 if a server has replicated a GTID. One can ask a node whether a GTID has been replicated and either get an immediate response (yes/no) or delay the reply until the node has replicated the GTID (wait for GTID). Currently only the first logic is used. We shall also support "wait for GTID". In that case we pick a candidate and wait until the candidate has replicated the GTID. This will lower the checking overhead as only one node is checked but not all configured nodes.
 +
 +Furthermore we can persist GTID/synchron-status information and attempt to reuse it. If we search for a candidate for the first time we query all configured nodes and persist their responses. The responses are cached and used for all subsequent read-only operations until a write is done. After the write we flush the cache and, if a read-only operation follows, we check again all nodes and cache their synchro-status.
  
  
pecl/mysqlnd_ms.txt · Last modified: 2017/09/22 13:28 by 127.0.0.1

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