ProxySQL does not automatically reopen backend connections when the last executed query was an INSERT that generated an auto-increment

[hujiko]

Hey,

I am experiencing some behavior, that looks like a bug to me:

When I

• connect through ProxySQL to my MySQL server and execute an INSERT statement (that succeeds fine)
• then terminate the connection between MySQL and ProxySQL (by executing KILL <process id> in a separate MySQL connection
• Then issue a simple SELECT * FROM mytable

I get the following error in the mysql client CLI:

ERROR 2013 (HY000): Lost connection to MySQL server during query

I would expect ProxySQL to reconnect to MySQL automatically without the client actually noticing anything.

I am running ProxySQL 2.4.2 on Ubuntu 20. My MySQL version is 8.0.27-18.1.
The MySQL-Cluster actually is a Galera Cluster, but as only one host is used and no read-write-splitting is configured, this should not matter.

And apparently in the exact same setup, ProxySQL does exactly this, when the last executed statement on the connection was a SELECT statement.

So the following combination works fine:

• connect through ProxySQL to my MySQL server and execute an INSERT statement (that succeeds fine)
• on the same connection execute a SELECT * FROM mytable
• then terminate the connection between MySQL and ProxySQL (by executing KILL <process id> in a separate MySQL connection
• Then issue a simple SELECT * FROM mytable

In this combination you will not see any error message in the client, as ProxySQL reconnect the backend connection automatically.

mySQL Servers:

mysql [myHost]> select * from runtime_mysql_servers;
+--------------+-------------+------+-----------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------------+
| hostgroup_id | hostname    | port | gtid_port | status | weight | compression | max_connections | max_replication_lag | use_ssl | max_latency_ms | comment       |
+--------------+-------------+------+-----------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------------+
| 10           | 10.12.64.48 | 3306 | 0         | ONLINE | 1      | 0           | 200             | 0                   | 0       | 0              | testing |
+--------------+-------------+------+-----------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------------+
1 row in set (0.00 sec)

Global Variables:

mysql [myHost]> select * from runtime_global_variables;
+----------------------------------------------------------------------+--------------------------------------------+
| variable_name                                                        | variable_value                             |
+----------------------------------------------------------------------+--------------------------------------------+
| admin-admin_credentials                                              | admin:admin;cluster1:secret1pass           |
| admin-stats_credentials                                              | stats:stats                                |
| admin-stats_mysql_connections                                        | 60                                         |
| admin-stats_mysql_connection_pool                                    | 60                                         |
| admin-stats_mysql_query_cache                                        | 60                                         |
| admin-stats_mysql_query_digest_to_disk                               | 0                                          |
| admin-stats_system_cpu                                               | 60                                         |
| admin-stats_system_memory                                            | 60                                         |
| admin-mysql_ifaces                                                   | 0.0.0.0:6032                               |
| admin-telnet_admin_ifaces                                            | (null)                                     |
| admin-telnet_stats_ifaces                                            | (null)                                     |
| admin-refresh_interval                                               | 2000                                       |
| admin-read_only                                                      | false                                      |
| admin-hash_passwords                                                 | true                                       |
| admin-vacuum_stats                                                   | true                                       |
| admin-version                                                        | 2.4.2-1-g2c8ac95                           |
| admin-cluster_username                                               | cluster1                                   |
| admin-cluster_password                                               | secret1pass                                |
| admin-cluster_check_interval_ms                                      | 200                                        |
| admin-cluster_check_status_frequency                                 | 100                                        |
| admin-cluster_mysql_query_rules_diffs_before_sync                    | 3                                          |
| admin-cluster_mysql_servers_diffs_before_sync                        | 3                                          |
| admin-cluster_mysql_users_diffs_before_sync                          | 3                                          |
| admin-cluster_proxysql_servers_diffs_before_sync                     | 3                                          |
| admin-cluster_mysql_variables_diffs_before_sync                      | 3                                          |
| admin-cluster_admin_variables_diffs_before_sync                      | 3                                          |
| admin-cluster_ldap_variables_diffs_before_sync                       | 3                                          |
| admin-cluster_mysql_query_rules_save_to_disk                         | true                                       |
| admin-cluster_mysql_servers_save_to_disk                             | true                                       |
| admin-cluster_mysql_users_save_to_disk                               | true                                       |
| admin-cluster_proxysql_servers_save_to_disk                          | true                                       |
| admin-cluster_mysql_variables_save_to_disk                           | true                                       |
| admin-cluster_admin_variables_save_to_disk                           | true                                       |
| admin-cluster_ldap_variables_save_to_disk                            | true                                       |
| admin-checksum_mysql_query_rules                                     | true                                       |
| admin-checksum_mysql_servers                                         | true                                       |
| admin-checksum_mysql_users                                           | true                                       |
| admin-checksum_mysql_variables                                       | true                                       |
| admin-checksum_admin_variables                                       | true                                       |
| admin-checksum_ldap_variables                                        | true                                       |
| admin-restapi_enabled                                                | false                                      |
| admin-restapi_port                                                   | 6070                                       |
| admin-web_enabled                                                    | false                                      |
| admin-web_port                                                       | 6080                                       |
| admin-web_verbosity                                                  | 0                                          |
| admin-prometheus_memory_metrics_interval                             | 61                                         |
| mysql-default_charset                                                | utf8                                       |
| mysql-default_collation_connection                                   | utf8_general_ci                            |
| mysql-shun_on_failures                                               | 5                                          |
| mysql-shun_recovery_time_sec                                         | 10                                         |
| mysql-unshun_algorithm                                               | 0                                          |
| mysql-query_retries_on_failure                                       | 1                                          |
| mysql-client_host_cache_size                                         | 0                                          |
| mysql-client_host_error_counts                                       | 0                                          |
| mysql-connect_retries_on_failure                                     | 10                                         |
| mysql-connect_retries_delay                                          | 1                                          |
| mysql-connection_delay_multiplex_ms                                  | 0                                          |
| mysql-connection_max_age_ms                                          | 0                                          |
| mysql-connect_timeout_client                                         | 10000                                      |
| mysql-connect_timeout_server                                         | 10000                                      |
| mysql-connect_timeout_server_max                                     | 10000                                      |
| mysql-enable_client_deprecate_eof                                    | true                                       |
| mysql-enable_server_deprecate_eof                                    | true                                       |
| mysql-enable_load_data_local_infile                                  | false                                      |
| mysql-eventslog_filename                                             |                                            |
| mysql-eventslog_filesize                                             | 104857600                                  |
| mysql-eventslog_default_log                                          | 0                                          |
| mysql-eventslog_format                                               | 1                                          |
| mysql-auditlog_filename                                              |                                            |
| mysql-auditlog_filesize                                              | 104857600                                  |
| mysql-handle_unknown_charset                                         | 1                                          |
| mysql-free_connections_pct                                           | 10                                         |
| mysql-connection_warming                                             | false                                      |
| mysql-session_idle_ms                                                | 1                                          |
| mysql-have_ssl                                                       | false                                      |
| mysql-have_compress                                                  | true                                       |
| mysql-interfaces                                                     | 0.0.0.0:6033                               |
| mysql-log_mysql_warnings_enabled                                     | false                                      |
| mysql-monitor_enabled                                                | false                                      |
| mysql-monitor_history                                                | 60000                                      |
| mysql-monitor_connect_interval                                       | 200000                                     |
| mysql-monitor_connect_timeout                                        | 600                                        |
| mysql-monitor_ping_interval                                          | 200000                                     |
| mysql-monitor_ping_max_failures                                      | 3                                          |
| mysql-monitor_ping_timeout                                           | 1000                                       |
| mysql-monitor_read_only_interval                                     | 1000                                       |
| mysql-monitor_read_only_timeout                                      | 800                                        |
| mysql-monitor_read_only_max_timeout_count                            | 3                                          |
| mysql-monitor_replication_lag_group_by_host                          | false                                      |
| mysql-monitor_replication_lag_interval                               | 10000                                      |
| mysql-monitor_replication_lag_timeout                                | 1000                                       |
| mysql-monitor_replication_lag_count                                  | 1                                          |
| mysql-monitor_groupreplication_healthcheck_interval                  | 5000                                       |
| mysql-monitor_groupreplication_healthcheck_timeout                   | 800                                        |
| mysql-monitor_groupreplication_healthcheck_max_timeout_count         | 3                                          |
| mysql-monitor_groupreplication_max_transactions_behind_count         | 3                                          |
| mysql-monitor_groupreplication_max_transactions_behind_for_read_only | 1                                          |
| mysql-monitor_galera_healthcheck_interval                            | 5000                                       |
| mysql-monitor_galera_healthcheck_timeout                             | 800                                        |
| mysql-monitor_galera_healthcheck_max_timeout_count                   | 3                                          |
| mysql-monitor_username                                               | monitor                                    |
| mysql-monitor_password                                               | monitor                                    |
| mysql-monitor_replication_lag_use_percona_heartbeat                  |                                            |
| mysql-monitor_query_interval                                         | 60000                                      |
| mysql-monitor_query_timeout                                          | 100                                        |
| mysql-monitor_slave_lag_when_null                                    | 60                                         |
| mysql-monitor_threads_min                                            | 8                                          |
| mysql-monitor_threads_max                                            | 128                                        |
| mysql-monitor_threads_queue_maxsize                                  | 128                                        |
| mysql-monitor_wait_timeout                                           | true                                       |
| mysql-monitor_writer_is_also_reader                                  | true                                       |
| mysql-max_allowed_packet                                             | 67108864                                   |
| mysql-tcp_keepalive_time                                             | 0                                          |
| mysql-use_tcp_keepalive                                              | false                                      |
| mysql-automatic_detect_sqli                                          | false                                      |
| mysql-firewall_whitelist_enabled                                     | false                                      |
| mysql-firewall_whitelist_errormsg                                    | Firewall blocked this query                |
| mysql-throttle_connections_per_sec_to_hostgroup                      | 1000000                                    |
| mysql-max_transaction_idle_time                                      | 14400000                                   |
| mysql-max_transaction_time                                           | 14400000                                   |
| mysql-multiplexing                                                   | true                                       |
| mysql-log_unhealthy_connections                                      | true                                       |
| mysql-enforce_autocommit_on_reads                                    | false                                      |
| mysql-autocommit_false_not_reusable                                  | false                                      |
| mysql-autocommit_false_is_transaction                                | false                                      |
| mysql-verbose_query_error                                            | false                                      |
| mysql-hostgroup_manager_verbose                                      | 1                                          |
| mysql-binlog_reader_connect_retry_msec                               | 3000                                       |
| mysql-threshold_query_length                                         | 524288                                     |
| mysql-threshold_resultset_size                                       | 4194304                                    |
| mysql-query_digests_max_digest_length                                | 2048                                       |
| mysql-query_digests_max_query_length                                 | 65000                                      |
| mysql-query_digests_grouping_limit                                   | 3                                          |
| mysql-query_digests_groups_grouping_limit                            | 0                                          |
| mysql-wait_timeout                                                   | 28800000                                   |
| mysql-throttle_max_bytes_per_second_to_client                        | 0                                          |
| mysql-throttle_ratio_server_to_client                                | 0                                          |
| mysql-max_connections                                                | 2048                                       |
| mysql-max_stmts_per_connection                                       | 20                                         |
| mysql-max_stmts_cache                                                | 10000                                      |
| mysql-mirror_max_concurrency                                         | 16                                         |
| mysql-mirror_max_queue_length                                        | 32000                                      |
| mysql-default_max_latency_ms                                         | 1000                                       |
| mysql-default_query_delay                                            | 0                                          |
| mysql-default_query_timeout                                          | 10000                                      |
| mysql-query_processor_iterations                                     | 0                                          |
| mysql-query_processor_regex                                          | 1                                          |
| mysql-set_query_lock_on_hostgroup                                    | 1                                          |
| mysql-reset_connection_algorithm                                     | 2                                          |
| mysql-auto_increment_delay_multiplex                                 | 5                                          |
| mysql-auto_increment_delay_multiplex_timeout_ms                      | 10000                                      |
| mysql-long_query_time                                                | 1000                                       |
| mysql-query_cache_size_MB                                            | 256                                        |
| mysql-ping_interval_server_msec                                      | 10000                                      |
| mysql-ping_timeout_server                                            | 200                                        |
| mysql-default_schema                                                 | information_schema                         |
| mysql-poll_timeout                                                   | 2000                                       |
| mysql-poll_timeout_on_failure                                        | 100                                        |
| mysql-server_capabilities                                            | 569899                                     |
| mysql-server_version                                                 | 5.5.30                                     |
| mysql-keep_multiplexing_variables                                    | tx_isolation,transaction_isolation,version |
| mysql-kill_backend_connection_when_disconnect                        | true                                       |
| mysql-client_session_track_gtid                                      | true                                       |
| mysql-sessions_sort                                                  | true                                       |
| mysql-session_idle_show_processlist                                  | true                                       |
| mysql-show_processlist_extended                                      | 0                                          |
| mysql-commands_stats                                                 | true                                       |
| mysql-query_digests                                                  | true                                       |
| mysql-query_digests_lowercase                                        | false                                      |
| mysql-query_digests_replace_null                                     | false                                      |
| mysql-query_digests_no_digits                                        | false                                      |
| mysql-query_digests_normalize_digest_text                            | false                                      |
| mysql-query_digests_track_hostname                                   | false                                      |
| mysql-query_digests_keep_comment                                     | false                                      |
| mysql-servers_stats                                                  | true                                       |
| mysql-default_reconnect                                              | true                                       |
| mysql-ssl_p2s_ca                                                     |                                            |
| mysql-ssl_p2s_capath                                                 |                                            |
| mysql-ssl_p2s_cert                                                   |                                            |
| mysql-ssl_p2s_key                                                    |                                            |
| mysql-ssl_p2s_cipher                                                 |                                            |
| mysql-ssl_p2s_crl                                                    |                                            |
| mysql-ssl_p2s_crlpath                                                |                                            |
| mysql-stacksize                                                      | 1048576                                    |
| mysql-threads                                                        | 4                                          |
| mysql-init_connect                                                   |                                            |
| mysql-ldap_user_variable                                             |                                            |
| mysql-add_ldap_user_comment                                          |                                            |
| mysql-default_tx_isolation                                           | READ-COMMITTED                             |
| mysql-default_session_track_gtids                                    | OFF                                        |
| mysql-connpoll_reset_queue_length                                    | 50                                         |
| mysql-min_num_servers_lantency_awareness                             | 1000                                       |
| mysql-aurora_max_lag_ms_only_read_from_replicas                      | 2                                          |
| mysql-stats_time_backend_query                                       | false                                      |
| mysql-stats_time_query_processor                                     | false                                      |
| mysql-query_cache_stores_empty_result                                | true                                       |
+----------------------------------------------------------------------+--------------------------------------------+
196 rows in set (0.00 sec)

Galera Hostgroups

mysql [myHost]> select * from runtime_mysql_galera_hostgroups;
+------------------+-------------------------+------------------+-------------------+--------+-------------+-----------------------+-------------------------+---------+
| writer_hostgroup | backup_writer_hostgroup | reader_hostgroup | offline_hostgroup | active | max_writers | writer_is_also_reader | max_transactions_behind | comment |
+------------------+-------------------------+------------------+-------------------+--------+-------------+-----------------------+-------------------------+---------+
| 10               | 11                      | 12               | 13                | 1      | 99          | 1                     | 99                      | abc     |
+------------------+-------------------------+------------------+-------------------+--------+-------------+-----------------------+-------------------------+---------+
1 row in set (0.00 sec)

Query Rules:

mysql [myHost]> select * from runtime_mysql_query_rules;
Empty set (0.00 sec)

[renecannao]

I think the subject of this issue should be: "[...] was an INSERT that generated an auto-increment" .
If proxysql doesn't automatically use a different backend connection it means that it really needed that specific connection = multiplexing was disabled.
If multiplexing is disabled, most probably your INSERT generated an auto-increment value. That causes multiplexing to be disabled for 5 queries, due to mysql-auto_increment_delay_multiplex set to 5.
Please try to set mysql-auto_increment_delay_multiplex to 0 and see if the issue goes away.

[mirostauder]

After some testing we can confirm that
multiplexing does not behave as expected in this case.
We will investigate how to fix this issue.