Both Percona and Maria allow MySQL to be configured to listen on an extra port when their thread pool is enable.
* https://www.percona.com/doc/percona-server/5.7/performance/threadpool.html
* https://mariadb.com/kb/en/the-mariadb-library/thread-pool-in-mariadb-51-53/
This is valuable because if the table has a lot of traffic (read or write load), gh-ost can end up starving the thread pool as incomming connections are immediately blocked.
By using gh-ost on the extra port, MySQL locking will still behave the same, but MySQL will keep a dedicated thread for each gh-ost connection.
When doing this, it's important to inspect the extra-max-connections variable. Both Percona and Maria default to 1, so gh-ost may easily exceed with its threads.
An example local run using this
```
$ mysql -S /tmp/mysql_sandbox20393.sock -e "select @@global.port, @@global.extra_port"
+---------------+---------------------+
| @@global.port | @@global.extra_port |
+---------------+---------------------+
| 20393 | 30393 |
+---------------+---------------------+
./bin/gh-ost \
--initially-drop-ghost-table \
--initially-drop-old-table \
--assume-rbr \
--port="20395" \
--assume-master-host="127.0.0.1:30393" \
--max-load=Threads_running=25 \
--critical-load=Threads_running=1000 \
--chunk-size=1000 \
--max-lag-millis=1500 \
--user="gh-ost" \
--password="gh-ost" \
--database="test" \
--table="mytable" \
--verbose \
--alter="ADD mynewcol decimal(11,2) DEFAULT 0.0 NOT NULL" \
--exact-rowcount \
--concurrent-rowcount \
--default-retries=120 \
--panic-flag-file=/tmp/ghost.panic.flag \
--postpone-cut-over-flag-file=/tmp/ghost.postpone.flag \
--execute
```
when throttling on user command there really is no need for injecting heartbeat. The user commanded, therefore gh-ost complies and trusts the reasoning for throttling. What this will allow is complete quiet time. This, in turn, will allow such features as relocating via orchestrator/pseudo-gtid at time of throttling
- Identifying textual characters sets; converting into specific type when applying dml events
- Refactored `ColumnsList`: introducing `Column` type
- Refactored `unsigned` handling, as part of `Column`
- `Column` type supports `convertArg()`: converting value of argument according to column data type
- DB URI attempts `utf8mb4,utf8,latin1` charsets in that order (first one to be recognized wins)
- Local tests filter by pattern
- Local tests append table schema on failure
- Local tests do not have postpone flag file
- Added character set local tests: `utf8`, `utf8mb4`, `latin1`
- `--max-lag-millis` is at least `100ms`
- `--heartbeat-interval-millis` introduced; defaults `500ms`, can range `100ms` - `1s`
- Control replicas lag calculated asynchronously to throttle test
- aggressive when `max-lag-millis < 1000` and when `replication-lag-query` is given
This will wait indefinitely for the replication status to change.
This allows us to run test schema changes in RDS without needing
custom RDS commands in gh-ost.
- Cutover would stall after `lock tables` wait-timeout due do waiting on a channel that would never be written to. This has been identified, reproduced, fixed, confirmed.
- Change of table names. Heres the story:
- Because were testing this even while `pt-online-schema-change` is being used in production, the `_tbl_old` naming convention makes for a collision.
- "old" table name is now `_tbl_del`, "del" standing for "delete"
- ghost table name is now `_tbl_gho`
- when issuing `--test-on-replica`, we keep the ghost table around, and were also briefly renaming original table to "old". Well this collides with a potentially existing "old" table on master (one that hasnt been dropped yet).
`--test-on-replica` uses `_tbl_ght` (ghost-test)
- similar problem with `--execute-on-replica`, and in this case the table doesnt stick around; calling it `_tbl_ghr` (ghost-replica)
- changelog table is now `_tbl_ghc` (ghost-changelog)
- To clarify, I dont want to go down the path of creating "old" tables with 2 or 3 or 4 or 5 or infinite leading underscored. I think this is very confusing and actually not operations friendly. Its OK that the migration will fail saying "hey, you ALREADY have an old table here, why dont you take care of it first", rather than create _yet_another_ `____tbl_old` table. Were always confused on which table it actually is that gets migrated, which is safe to `drop`, etc.
- just after rowcopy completing, just before cutover, during cutover: marking as point in time _of interest_ so as to increase logging frequency.
- Rowcopy time is bounded by copy end-time
- Retries are configurable via `--default-retries` (default: `60`)
- `migrator` notes the hostname
- `applier` and `inspector` note `impliedKey` (`@@hostname` and `@@port`)
- Added lots of code comments
- Adding documentation for "triggerless design"
- Supporting multi-step, safe cut-over phase, where queries are blocked throughout the phase, and worst case scenario is table outage (no data corruption)
- Self-rollsback in case of failure (restored original table)
- Supporting `--allow-nullable-unique-key`
- Tool will bail out if chosen key has nullable columns and the above is not provided
- Fixed `OriginalBinlogRowImage` comaprison (lower/upper case issue)
- Introduced reasonable streamer reconnect sleep time
- Operation would terminate after events lock noticed but before applying all events: race condition where the event would be captured asynchronously. The event is now handled sequentially with the DML events, hence now safe.
- Multiple rowcopy operations would still write to `rowCopyComplete` channel. This is still the case, but now we only wait for the first and then just flush (read and discard) any others, to avoid blocking
- Events DML listener is only added after table creation: the problem was that with very busy tables, the events func buffer would fill up, and the "tables-created" event would be blocked.
- `waitForEventsUpToLock()` unifies the waiting on all variants of complete-migration
- With `--test-on-replica`, now stopping replication "nicely", using `master_pos_wait()`
- With `--test-on-replica`, not throttling on replication after replication is stopped (duh)
- More debug output
- Introduced `SwapTablesTimeoutSeconds`; `RENAME` is limited by this timeout
- If `RENAME` fails (due to the above), we throttle and retry
- `SwapTablesAtomic()` sets `lock_wait_timeout` and notifies with connection id
- `GrabVoluntaryLock()` intentionally grabs (and later releases) voluntary lock. It notifies when it is taken and awaits instructions as for when it could be released.
- `IssueBlockingQueryOnVoluntaryLock()` does what it says. It notifies with its connection_id so that it can be easily traced
- `stopWritesAndCompleteMigrationOnMasterViaLock()` does the thang. Oh dear this was agonizing and the code is a pain to look at, though under the limitations I do believe it is as clean as I could hope for.
- Added `switch-to-rbr` flag; applying binlog format change if needed
- Using dedicated db instance for locking & renaming on applier (must be used from within same connection)
- Heartbeat now uses `time.RFC3339Nano`
- Swap tables works! Caveat: short table outage
- `--test-on-replica` works!
- retries: using `panicAbort`: from any goroutine, regardless of context, it is possible to terminate the operation
- Reintroduced changelog events listener on streamer. This is the correct implementation.
- `INSERT`, `DELETE`, `UPDATE` statements
- support for `--noop`
- initial support for `--test-on-replica`. Verifying against `--allow-on-master`
- Changelog events no longer read from binlog stream, because reading it may be throttled, and we have to be able to keep reading the heartbeat and state events.
They are now being read directly from table, mapping already-seen-events to avoid confusion
Changlelog listener pools table in 2*frequency of heartbeat injection
- Throttling variables protected by mutex
- Added `--throttle-additional-flag-file`: `operation pauses when this file exists; hint: keep default, use for throttling multiple gh-osc operations`
- ColumnList is not a `struct` which contains ordinal mapping
- More implicit write changelog + audit changelog
- builder now builds `DELETE` and `INSERT` queries from data it will eventually get from DML event
- Sanity check for binlog_row_image
- Restarting replication to be sure binlog settings apply
- Prepare for accepting `SIGHUP` (reloading configuration)
- Supporting `--throttle-file-flag`
- Printing status
- Supporting transactional table syntax
- code cleanup; refactoring
- proper use of atomic where required
- iterations are in changelog (erm... maybe too much)
- `LOCK TABLES`, `UNLOCK TABLES` working
- Using heartbeat
- Throttling works based on heartbeat
- Refactored binlog_reader stuff. Now streaming events (into golang channel, which makes for nice buffering and throttling)
- Binlog table listeners work
- More Migrator logic; existing logic for waiting on `state` events (e.g. `TablesCreatedState`)
