Check that `auto_vacuum` is disabled when porting a SQLite database to Postgres, as `VACUUM`s must not be performed between runs of the script. (#13195)

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reivilibre 2022-07-07 11:08:04 +01:00 committed by GitHub
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changelog.d/13195.misc Normal file
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@ -0,0 +1 @@
Check that `auto_vacuum` is disabled when porting a SQLite database to Postgres, as `VACUUM`s must not be performed between runs of the script.

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@ -143,6 +143,14 @@ to do step 2.
It is safe to at any time kill the port script and restart it.
However, under no circumstances should the SQLite database be `VACUUM`ed between
multiple runs of the script. Doing so can lead to an inconsistent copy of your database
into Postgres.
To avoid accidental error, the script will check that SQLite's `auto_vacuum` mechanism
is disabled, but the script is not able to protect against a manual `VACUUM` operation
performed either by the administrator or by any automated task that the administrator
may have configured.
Note that the database may take up significantly more (25% - 100% more)
space on disk after porting to Postgres.

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@ -621,6 +621,25 @@ class Porter:
self.postgres_store.db_pool.updates.has_completed_background_updates()
)
@staticmethod
def _is_sqlite_autovacuum_enabled(txn: LoggingTransaction) -> bool:
"""
Returns true if auto_vacuum is enabled in SQLite.
https://www.sqlite.org/pragma.html#pragma_auto_vacuum
Vacuuming changes the rowids on rows in the database.
Auto-vacuuming is therefore dangerous when used in conjunction with this script.
Note that the auto_vacuum setting can't be changed without performing
a VACUUM after trying to change the pragma.
"""
txn.execute("PRAGMA auto_vacuum")
row = txn.fetchone()
assert row is not None, "`PRAGMA auto_vacuum` did not give a row."
(autovacuum_setting,) = row
# 0 means off. 1 means full. 2 means incremental.
return autovacuum_setting != 0
async def run(self) -> None:
"""Ports the SQLite database to a PostgreSQL database.
@ -637,6 +656,21 @@ class Porter:
allow_outdated_version=True,
)
# For safety, ensure auto_vacuums are disabled.
if await self.sqlite_store.db_pool.runInteraction(
"is_sqlite_autovacuum_enabled", self._is_sqlite_autovacuum_enabled
):
end_error = (
"auto_vacuum is enabled in the SQLite database."
" (This is not the default configuration.)\n"
" This script relies on rowids being consistent and must not"
" be used if the database could be vacuumed between re-runs.\n"
" To disable auto_vacuum, you need to stop Synapse and run the following SQL:\n"
" PRAGMA auto_vacuum=off;\n"
" VACUUM;"
)
return
# Check if all background updates are done, abort if not.
updates_complete = (
await self.sqlite_store.db_pool.updates.has_completed_background_updates()