From 6534b804a57d5f6cfc40ca7f63a64d1c5153748f Mon Sep 17 00:00:00 2001 From: Hallvard Furuseth Date: Sun, 23 Aug 2015 22:00:14 +0200 Subject: [PATCH] mdb_page_alloc(): Use original snapshot of freeDB. I can't help thinking this should be safer, and useful somewhere. --- libraries/liblmdb/mdb.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c index d2b1d57199..67c2f2d5bb 100644 --- a/libraries/liblmdb/mdb.c +++ b/libraries/liblmdb/mdb.c @@ -1300,6 +1300,8 @@ struct MDB_cursor { #define C_UNTRACK 0x40 /**< Un-track cursor when closing */ #define C_WRITEMAP MDB_TXN_WRITEMAP /**< Copy of txn flag */ /** Read-only cursor into the txn's original snapshot in the map. + * Set for read-only txns, and in #mdb_page_alloc() for #FREE_DBI when + * #MDB_DEVEL & 2. Only implements code which is necessary for this. */ #define C_ORIG_RDONLY MDB_TXN_RDONLY /** @} */ @@ -2259,6 +2261,8 @@ mdb_page_dirty(MDB_txn *txn, MDB_page *mp) * Do not modify the freedB, just merge freeDB records into me_pghead[] * and move me_pglast to say which records were consumed. Only this * function can create me_pghead and move me_pglast/mt_next_pgno. + * When #MDB_DEVEL & 2, it is not affected by #mdb_freelist_save(): it + * then uses the transaction's original snapshot of the freeDB. * @param[in] mc cursor A cursor handle identifying the transaction and * database for which we are allocating. * @param[in] num the number of pages to allocate. @@ -2334,6 +2338,14 @@ mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp) last = env->me_pglast; oldest = env->me_pgoldest; mdb_cursor_init(&m2, txn, FREE_DBI, NULL); +#if (MDB_DEVEL) & 2 /* "& 2" so MDB_DEVEL=1 won't hide bugs breaking freeDB */ + /* Use original snapshot. TODO: Should need less care in code + * which modifies the database. Maybe we can delete some code? + */ + m2.mc_flags |= C_ORIG_RDONLY; + m2.mc_db = &env->me_metas[(txn->mt_txnid-1) & 1]->mm_dbs[FREE_DBI]; + m2.mc_dbflag = (unsigned char *)""; /* probably unnecessary */ +#endif if (last) { op = MDB_SET_RANGE; key.mv_data = &last; /* will look up last+1 */ @@ -3260,6 +3272,9 @@ mdb_txn_abort(MDB_txn *txn) /** Save the freelist as of this transaction to the freeDB. * This changes the freelist. Keep trying until it stabilizes. + * + * When (MDB_DEVEL) & 2, the changes do not affect #mdb_page_alloc(), + * it then uses the transaction's original snapshot of the freeDB. */ static int mdb_freelist_save(MDB_txn *txn) -- 2.39.5