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Phase 0: logical DB dump/restore without external tools (spike C)

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DbDumper reads every prefixed table through the Nextcloud connection in
one REPEATABLE READ (read-only) transaction, with keyset pagination on
the primary key, and streams each table as JSON lines into its own blob
stream (BlobWriter), so unchanged tables are deduplicated. Restore
replaces table contents in one transaction and resets PostgreSQL
sequences.

Spike C (NC34, PostgreSQL, standard image without pg_dump/pgsql ext):
300k-row table with bytea: dump 6.3s / 50 MiB peak, 94 MiB JSON -> 20 MiB
stored; unchanged second dump stores nothing; restore makes every table
checksum-identical and all 110 sequences continue above the maximum.
This commit is contained in:
Dillard Blom
2026-10-01 18:26:27 +02:00
parent 1839997972
commit 915e534ab2
4 changed files with 443 additions and 0 deletions
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spikes/03-db-dump.php
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<?php
declare(strict_types=1);
// Spike C: logical DB dump/restore through the Nextcloud connection (no pg_dump/mysqldump).
// Run inside a Nextcloud container as the web user:
// php -d memory_limit=128M /var/www/html/custom_apps/ng_backup/spikes/03-db-dump.php /tmp/ngb-db-repo
require '/var/www/html/lib/base.php';
set_exception_handler(null);
restore_error_handler();
require __DIR__ . '/bootstrap.php';
use OCA\NgBackup\Backend\LocalBackend;
use OCA\NgBackup\Db\DbDumper;
use OCA\NgBackup\Repository\Repository;
$repoDir = $argv[1] ?? '/tmp/ngb-db-repo';
exec('rm -rf ' . escapeshellarg($repoDir));
$ok = true;
$check = static function (string $name, bool $pass) use (&$ok): void {
printf("%-62s %s\n", $name, $pass ? 'PASS' : 'FAIL');
$ok = $ok && $pass;
};
/** @var \OC\DB\ConnectionAdapter $adapter */
$adapter = \OCP\Server::get(\OCP\IDBConnection::class);
$db = $adapter->getInner();
$prefix = \OCP\Server::get(\OCP\IConfig::class)->getSystemValueString('dbtableprefix', 'oc_');
$dumper = new DbDumper($db, $prefix);
printf("database: %s, prefix %s\n", get_class($db->getDatabasePlatform()), $prefix);
$tables = array_values(array_filter($db->createSchemaManager()->listTableNames(), fn ($t) => str_starts_with($t, $prefix)));
sort($tables);
$before = [];
foreach ($tables as $t) {
$before[$t] = $dumper->checksum($t);
}
printf("%d tables, %d rows\n", count($tables), array_sum(array_column($before, 'rows')));
$repo = Repository::init(new LocalBackend($repoDir), 'spike passphrase');
memory_reset_peak_usage();
$stats = ['newBlobs' => 0, 'dupBlobs' => 0, 'uploaded' => 0];
$t = microtime(true);
$manifest = $dumper->dump($repo, $stats);
$repo->putObject('db/1', json_encode($manifest, JSON_THROW_ON_ERROR));
printf("dump 1: %.1fs, peak %.1f MiB, %s\n", microtime(true) - $t, memory_get_peak_usage() / 1048576, json_encode($stats));
$dumpBytes = array_sum(array_column($manifest['tables'], 'bytes'));
printf("dump size (plain JSON lines): %.1f MiB\n", $dumpBytes / 1048576);
$check('checksums in dump match live tables', array_map(fn ($x) => $x['sha256'], $manifest['tables']) === array_map(fn ($x) => $x['sha256'], $before));
// Second dump without changes: blobs are reused.
$stats2 = ['newBlobs' => 0, 'dupBlobs' => 0, 'uploaded' => 0];
$dumper->dump($repo, $stats2);
printf("dump 2 (no changes): %s\n", json_encode($stats2));
$check('unchanged database: (almost) nothing new stored', $stats2['uploaded'] < 0.05 * max(1, $stats['uploaded']));
// Damage the database.
$db->executeStatement('DELETE FROM ' . $prefix . 'filecache WHERE path LIKE ?', ['files/Docs/%']);
$db->executeStatement('UPDATE ' . $prefix . 'appconfig SET configvalue = ? WHERE appid = ? AND configkey = ?', ['damaged', 'core', 'installedat']);
$db->insert($prefix . 'users', ['uid' => 'intruder', 'displayname' => 'Intruder', 'password' => 'x', 'uid_lower' => 'intruder']);
$changed = array_filter($tables, fn ($tb) => $dumper->checksum($tb)['sha256'] !== $before[$tb]['sha256']);
printf("tables changed by the damage: %s\n", implode(', ', $changed));
$check('damage visible in checksums', count($changed) >= 3);
// Restore.
memory_reset_peak_usage();
$t = microtime(true);
$repo2 = Repository::open(new LocalBackend($repoDir), 'spike passphrase');
$m = json_decode($repo2->getObject('db/1'), true, 512, JSON_THROW_ON_ERROR);
$rows = $dumper->restore($repo2, $m);
printf("restore: %d rows in %.1fs, peak %.1f MiB\n", $rows, microtime(true) - $t, memory_get_peak_usage() / 1048576);
$mismatch = [];
foreach ($tables as $tb) {
$after = $dumper->checksum($tb);
if ($after !== $before[$tb]) {
$mismatch[] = $tb;
}
}
$check('after restore: every table identical to before', $mismatch === []);
if ($mismatch) {
echo 'mismatch: ' . implode(', ', $mismatch) . "\n";
}
// Sequences must continue after the restored maximum (PostgreSQL).
if ($db->getDatabasePlatform() instanceof \Doctrine\DBAL\Platforms\PostgreSQLPlatform) {
$serials = $db->fetchAllAssociative("SELECT table_name, column_name, pg_get_serial_sequence(table_name, column_name) AS seq
FROM information_schema.columns WHERE table_schema = current_schema() AND table_name LIKE ?
AND pg_get_serial_sequence(table_name, column_name) IS NOT NULL", [$prefix . '%']);
$bad = [];
foreach ($serials as $s) {
$max = (int)$db->fetchOne(sprintf('SELECT COALESCE(MAX(%s), 0) FROM %s', $db->quoteIdentifier($s['column_name']), $db->quoteIdentifier($s['table_name'])));
$seq = $db->fetchAssociative('SELECT last_value, is_called FROM ' . $s['seq']);
$next = (int)$seq['last_value'] + ($seq['is_called'] ? 1 : 0);
if ($next <= $max) {
$bad[] = "{$s['table_name']}.{$s['column_name']} next=$next max=$max";
}
}
$check(sprintf('all %d sequences continue above the restored maximum', count($serials)), $bad === []);
if ($bad) {
echo implode("\n", $bad), "\n";
}
}
exec('rm -rf ' . escapeshellarg($repoDir));
echo $ok ? "ALL PASS\n" : "FAILURES\n";
exit($ok ? 0 : 1);