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* Fix concurrency issues in download-using-manifests' handling of the

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SQLite manifest cache.  The DBI AutoCommit feature caused every
  process to have an active transaction at all times, which could
  indefinitely block processes wanting to update the manifest cache.

* Disable fsync() in the manifest cache because we don't need
  integrity (the cache can always be recreated if it gets corrupted).
This commit is contained in:
Eelco Dolstra 2011-07-13 14:05:54 +00:00
parent 0a623a10c7
commit e649f3168b
2 changed files with 12 additions and 1 deletions
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7
scripts/NixManifest.pm.in
View File

@ -219,11 +219,12 @@ sub updateManifestDB {
# Open/create the database.
our $dbh = DBI->connect("dbi:SQLite:dbname=$dbPath", "", "")
or die "cannot open database `$dbPath'";
$dbh->{AutoCommit} = 0;
$dbh->{RaiseError} = 1;
$dbh->{PrintError} = 0;
$dbh->do("pragma foreign_keys = on");
$dbh->do("pragma synchronous = off"); # we can always reproduce the cache
$dbh->do("pragma journal_mode = truncate");
# Initialise the database schema, if necessary.
$dbh->do(<<EOF);
@ -278,6 +279,8 @@ EOF
open MAINLOCK, ">>$manifestDir/cache.lock" or die;
flock(MAINLOCK, LOCK_EX) or die;
$dbh->begin_work;
# Read each manifest in $manifestDir and add it to the database,
# unless we've already done so on a previous run.
my %seen;
@ -291,6 +294,8 @@ EOF
"select 1 from Manifests where path = ? and timestamp = ?",
{}, $manifest, $timestamp)} == 1;
print STDERR "caching $manifest...\n";
$dbh->do("delete from Manifests where path = ?", {}, $manifest);
$dbh->do("insert into Manifests(path, timestamp) values (?, ?)",

6
scripts/download-using-manifests.pl.in
View File

@ -267,6 +267,12 @@ my @path = computeSmallestDownload $targetPath;
die "don't know how to produce $targetPath\n" if scalar @path == 0;
# We don't need the manifest anymore, so close it as an optimisation:
# if we still have SQLite locks blocking other processes (we
# shouldn't), this gets rid of them.
$dbh->disconnect;
# Traverse the shortest path, perform the actions described by the
# edges.
my $curStep = 1;