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lib ldb: lmdb clear stale readers on write txn start

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In use process failures and Bind9 shut downs leave stale entries in the
lmdb reader table.  This can result in lmdb filling it's database file, as
the free list can not be reclaimed due to the stale reader.

In this fix we call mdb_reader_check at the start of each transaction,
to free any stale readers.  As the default maximum number of readers is
127, this should not impact on performance to any great extent.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14330

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Tue Mar 31 01:26:07 UTC 2020 on sn-devel-184
This commit is contained in:
Gary Lockyer 2020-03-30 12:08:30 +13:00 committed by Andrew Bartlett
parent 1cc250b46e
commit 89041a6d18
2 changed files with 23 additions and 1 deletions
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17
lib/ldb/ldb_mdb/ldb_mdb.c
View File

@ -641,6 +641,23 @@ static int lmdb_transaction_start(struct ldb_kv_private *ldb_kv)
return LDB_ERR_PROTOCOL_ERROR;
}
/*
* Clear out any stale readers
*/
{
int stale;
mdb_reader_check(lmdb->env, &stale);
if (stale > 0) {
ldb_debug(
lmdb->ldb,
LDB_DEBUG_ERROR,
"LMDB Stale readers, deleted (%d)",
stale);
}
}
ltx_head = lmdb_private_trans_head(lmdb);
tx_parent = lmdb_trans_get_tx(ltx_head);

7
lib/ldb/tests/ldb_lmdb_free_list_test.c
View File

@ -617,7 +617,12 @@ static void test_free_list_stale_reader(void **state)
ret = ldb_kv->kv_ops->finish_write(ldb_kv);
assert_int_equal(ret, LDB_SUCCESS);
}
assert_int_equal(ret, LDB_ERR_BUSY);
/*
* We now do an explicit clear of stale readers at the start of a
* write transaction so should not get LDB_ERR_BUSY any more
* assert_int_equal(ret, LDB_ERR_BUSY);
*/
assert_int_equal(ret, LDB_SUCCESS);
assert_int_not_equal(i, 0);
/*