pecl:mysqlnd_ms
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pecl:mysqlnd_ms [2012/04/17 11:48] – [Raw Bin ideas (RFCs)] uw | pecl:mysqlnd_ms [2012/08/10 09:13] – [Development steps (release planning)] uw | ||
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=== 1.4 - Tweaking based on user feedback | === 1.4 - Tweaking based on user feedback | ||
+ | |||
+ | == Coding/ | ||
+ | |||
+ | * [done] More fail over options | ||
+ | * [done] 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 " | ||
+ | * [done] Remember failed hosts for the duration of a web request (the plugins' | ||
+ | |||
+ | * [done] Refine QoS session consistency server selection policy | ||
+ | * [done] 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. | ||
+ | |||
+ | * [done] Improve load balancing | ||
+ | * [done] Allow users to set a ratio/ | ||
+ | |||
+ | == QA == | ||
+ | |||
+ | * [done] 85-90% code coverage through tests | ||
+ | |||
+ | == Documentation, | ||
+ | |||
+ | * [done] Update documentation | ||
+ | * [done] Assorted blog postings | ||
+ | |||
+ | === 1.5 - Tweaking based on user feedback | ||
+ | |||
+ | Work has not started yet. | ||
== Coding/ | == Coding/ | ||
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* [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. | * NOTE: this may require refactoring of four filters. | ||
- | * [open] | + | * [open] |
* [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] 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] 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] Allow users to set a ratio/ | ||
* [open] Work with php.net Windows team to provide PECL/ | * [open] Work with php.net Windows team to provide PECL/ | ||
+ | * Ensure the code builds | ||
+ | * Encourage Windows team to create builds | ||
== QA == | == QA == | ||
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* [open] Update documentation | * [open] Update documentation | ||
* [open] Assorted blog postings | * [open] Assorted blog postings | ||
- | |||
- | === Open and delayed tasks === | ||
- | |||
- | == Coding/ | ||
- | |||
- | * [incomplete - 1.2] make load balancer schemata aware | ||
- | * for each statement detect database/ | ||
- | * follow schemata based partitioning rules | ||
- | * basic idea: http:// | ||
- | * cancelled/ | ||
- | * [cancelled] improve trx_stickiness using MYSQL*/ | ||
- | * cancelled: http:// | ||
- | * [open] bail on unknown config settings. For example, bail if someone uses round_robin instead of roundrobin | ||
- | |||
- | == QA == | ||
- | |||
- | * [open] >= 90% code coverage through tests | ||
- | * [open] write report on parsing overhead, goal: <5% in worst case micro benchmarks | ||
- | |||
- | == Documentation, | ||
- | |||
- | * [done] impact of connection limits such as allow_persistent, | ||
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== Feature description == | == Feature description == | ||
- | === Eventual consistent: automatic chaining of PECL/ | + | === More fail over configuration options |
== Problem to solve / Idea == | == Problem to solve / Idea == | ||
- | MySQL replication is asynchronous. Slaves are //eventual consistent// | + | Whenever the plugin tries to connect to a node it may fail to do so. Connection attempts can be made when opening |
- | 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 | + | The fail over logic itself |
- | + | ||
- | For certain queries, PECL/ | + | |
- | + | ||
- | (MySQL semi-synchronous replication does not change the matter as it requires only one slave to have received but not yet applied the update.) | + | |
- | + | ||
- | **PECL/ | + | |
== Feature description == | == Feature description == | ||
- | Applications shall be able to define a " | ||
- | * [RW_]CONSISTENT | + | Automatic |
- | * [RO_]EVENTUAL_CONSISTENT | + | |
- | + | ||
- | With CONSISTENT every statement shall be run on the master to avoid stale data. EVENTUAL_CONSISTENT allows the use of slaves and thus, stale, non-consistent data may be read. | + | |
- | + | ||
- | PECL/ | + | |
- | + | ||
- | However, PECL/ | + | |
- | + | ||
- | /* Force use of master - consistent read although no SQL hint is used */ | + | |
- | mysqlnd_ms_set_service_level($link, | + | |
- | $link-> | + | |
- | $link-> | + | |
- | + | ||
- | /* Use master or slaves for reads - allow read stale, non-consistent data is acceptable */ | + | |
- | mysqlnd_ms_set_service_level($link, | + | |
- | $link-> | + | |
- | + | ||
- | The service level EVENTUAL_CONSISTENT can be combined with automatic, local caching. It shall be configurable if and for which queries caching shall be used. Configuration can, for example, be done via the PECL/ | + | |
- | + | ||
- | If PECL/ | + | |
- | + | ||
- | Use and integration of PECL/ | + | |
- | + | ||
- | + | ||
- | === Global Transaction ID === | + | |
- | == Problem to solve / Idea == | + | |
- | + | ||
- | In the scope of MySQL master - slave replication global transaction IDs can be understood as a measure to identify a database state. Replicas/ | + | |
- | + | ||
- | The MySQL built-in replication does not feature global transaction IDs. MySQL replication uses transaction log files and log file positions to identify change sets that replicas (slaves) need to apply. Log file and log file position are local to a machine. A tuple of (log file, log file position) does not uniquely identify a change set in the whole cluster. | + | |
- | + | ||
- | If, for example, your setup is A -> B -> C (A is the master, B is a slave reading from A, C is a slave reading from B) and B fails you are faced with the challenge to identify the log file and log file position on A from which C shall continue to read and apply change sets. C cannot continue reading from the same (log file, log position) as it was reading from B. The tuple (log file=2, log position=17) on B can identify a different change set than the tuple (log file=2, log position=17) on A. C might get out of sync, loose change sets or apply them multiple times, if it would blindly continue reading from the same position on A. | + | |
- | + | ||
- | Today, it can become a bit of a time consuming guessing game to identify the next change set that B needs to process in this fail-over example. | + | |
- | + | ||
- | Fail-over and circular-replication | + | |
- | + | ||
- | The plugin | + | |
- | + | ||
- | == Feature description == | + | |
- | + | ||
- | Global transaction IDs can be used for multiple purposes: | + | |
- | + | ||
- | * Simplify server fail-over (server-side, | + | |
- | + | ||
- | * Monitor slave replication status (client-side, | + | |
- | * Identify " | + | |
- | * Identify slaves which are " | + | |
- | * Let the load balancer skip slaves which have fallen to far behind to reduce their load | + | |
- | + | ||
- | The plugin shall support using a global transaction ID for: | + | |
- | + | ||
- | - server fail-over (e.g. promoting new master after master failure) | + | |
- | - selection of " | + | |
- | + | ||
- | Gobal transaction ID generation shall be done by SQL injection. The plugin shall insert SQL at the end of each (write) transaction (see http:// | + | |
- | + | ||
- | The SQL used for globals transaction ID generation can be different for the different purposes. It may be good enough to inject SET @_g_trx_id=UUID_SHORT() on the master before a SQL transaction commits to help with fail-over. Whereas the selection of slaves of a certain state (" | + | |
- | + | ||
- | Thus, the user shall be able to configure: | + | |
- | + | ||
- | * SQL used for ID generation | + | |
- | * SQL used to retrieve ID | + | |
- | + | ||
- | If no SQL is given to retrieve the ID, the plugin does not feature '2) selection of " | + | |
- | + | ||
- | This is useful if, for example, an application does a write and needs to read the modified data " | + | |
- | + | ||
- | /* write to master */ | + | |
- | $link-> | + | |
- | $write_trx_id = mysqlnd_ms_get_last_global_transaction_id(); | + | |
- | + | ||
- | /* Force use of master - consistent read although no SQL hint is used */ | + | |
- | mysqlnd_ms_set_service_level($link, | + | |
- | $link-> | + | |
- | $link-> | + | |
- | + | ||
- | /* Read from a slave which has replicated global transaction ID or, if no slave found, use master */ | + | |
- | mysqlnd_ms_set_service_level($link, | + | |
- | $link-> | + | |
- | $link-> | + | |
- | + | ||
- | /* Use master or slaves for reads - allow read stale, non-consistent data is acceptable */ | + | |
- | mysqlnd_ms_set_service_level($link, | + | |
- | $link-> | + | |
- | + | ||
- | The global transaction ID feature of the plugin is turned off by default. The feature is seen as an experts topic. | + | |
- | + | ||
- | === mysqlnd_ms_change_user() === | + | |
- | == Problem to solve / Idea == | + | |
- | + | ||
- | Give users a way to overrule all automatic decisions, including the use of host credentials from the config when broadcasting COM_CHANGE_USER after mysqlnd_change_user(master_user, | + | |
- | + | ||
- | == Feature description == | + | |
- | + | ||
- | bool mysqlnd_ms_change_user(mixed $connection, | + | |
- | + | ||
- | $where: MYSQLND_MS_ALL_CONNECTIONS, | + | |
- | + | ||
- | Consider: | + | |
- | + | ||
- | $where: MYSQLND_MS_ALL_CONNECTIONS, | + | |
- | + | ||
- | === mysqlnd_ms_get_errors() === | + | |
- | == Problem to solve / Idea == | + | |
- | + | ||
- | Not all MS errors can be bubbled up through the standard APIs. For example, failing to parse parts of the MS config may result in connection error. Upon connect, the user will get the error code for the failed connect. However, the failure to parse the config, the cause of the problem, is only shown as a warning. | + | |
- | + | ||
- | == Feature description == | + | |
- | + | ||
- | array mysqlnd_ms_get_errors([mixed $connection]) | + | |
- | + | ||
- | TDB. | + | |
- | + | ||
- | === More fail over configuration options === | + | |
- | == Problem to solve / Idea == | + | |
- | + | ||
- | Whenever the plugin tries to connect to a node it may fail to do so. Connection attempts can be made when opening a connection or later, when executing a statement (lazy connections). By default the plugin bails out if the connection attempt fails. To make using the plugin as transparent as possible it is possible to optionally enable automatic fail over in case of failed connection attempts. | + | |
- | + | ||
- | + | ||
- | == Feature description == | + | |
- | Up to version 1.3 the automatic | + | - make it configurable whether |
+ | - link fail over to certain error codes | ||
+ | - remember failed hosts to skip them for the rest of the web request | ||
- | In the future the search for an alternative shall not stop after B but continue until a connection has been established or there are no alternatives. If a connect to A fails, the plugin shall try B, C, D and so forth. Automatic fail over, automatic connection attempts shall not stop after trying B and failing to connect to B. | + | Up to version 1.3 the automatic fail over stops after trying one alternative. For example, if a connection to A fails we try B. If connecting to B fails we stop and bail out. In that case the user must handle the error although there may be node C and D, ... which could be used. In the future the search for an alternative shall not stop after B but continue until a connection has been established or there are no alternatives. If a connect to A fails, the plugin shall try B, C, D and so forth. Automatic fail over, automatic connection attempts shall not stop after trying B and failing to connect to B. |
Whether this shall become a new default or become configurable is to be decided. | Whether this shall become a new default or become configurable is to be decided. | ||
Furthermore, | Furthermore, | ||
+ | |||
+ | Upon request the plugin will remember failed nodes for the duration of a web request. If connecting to a node has failed once no further attempts will be made to connect to the node. This may lead to situations where nodes are skipped although they became available again in the meantime. This is ignore because most web requests are short-lived. | ||
=== Support directing statements manually to a group of nodes for more efficient server cache usage === | === Support directing statements manually to a group of nodes for more efficient server cache usage === | ||
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== Problem to solve / Idea == | == 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. The load shall be optionally reduced with tweaking settings. | + | 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 == | == Feature description == | ||
+ | |||
+ | Two additional ways for finding candidates help lowering the overhead: | ||
+ | |||
+ | * Wait for GTID | ||
+ | * Cache/ | ||
+ | |||
+ | 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/ | ||
+ | |||
+ |
pecl/mysqlnd_ms.txt · Last modified: 2017/09/22 13:28 by 127.0.0.1