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mdbx: fix DB-shrinking race with copy-asis & readers.
Change-Id: I1e05616de03d814850a1c8ad20e83941b2d1c911
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@ -259,11 +259,14 @@ typedef struct MDBX_reader {
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volatile mdbx_pid_t mr_pid;
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/* The thread ID of the thread owning this txn. */
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volatile mdbx_tid_t mr_tid;
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/* The number of pages used in the reader's MVCC snapshot,
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* i.e. the value of meta->mm_geo.next and txn->mt_next_pgno */
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volatile pgno_t mr_snapshot_pages;
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/* cache line alignment */
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uint8_t pad[MDBX_CACHELINE_SIZE -
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(sizeof(txnid_t) + sizeof(mdbx_pid_t) + sizeof(mdbx_tid_t)) %
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MDBX_CACHELINE_SIZE];
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uint8_t pad[MDBX_CACHELINE_SIZE - (sizeof(txnid_t) + sizeof(mdbx_pid_t) +
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sizeof(mdbx_tid_t) + sizeof(pgno_t)) %
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MDBX_CACHELINE_SIZE];
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} MDBX_reader;
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/* Information about a single database in the environment. */
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59
src/mdbx.c
59
src/mdbx.c
@ -2163,7 +2163,7 @@ static txnid_t mdbx_find_oldest(MDBX_txn *txn) {
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mdbx_tassert(txn, edge <= txn->mt_txnid - 1);
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MDBX_lockinfo *const lck = env->me_lck;
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if (unlikely(env->me_lck == NULL /* exclusive mode */))
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if (unlikely(lck == NULL /* exclusive mode */))
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return env->me_oldest_stub = edge;
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const txnid_t last_oldest = lck->mti_oldest;
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@ -2201,6 +2201,25 @@ static txnid_t mdbx_find_oldest(MDBX_txn *txn) {
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return oldest;
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}
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/* Find largest mvcc-snapshot still referenced. */
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static pgno_t mdbx_find_largest(MDBX_env *env, pgno_t largest) {
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MDBX_lockinfo *const lck = env->me_lck;
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if (likely(lck != NULL /* exclusive mode */)) {
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const unsigned snap_nreaders = lck->mti_numreaders;
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for (unsigned i = 0; i < snap_nreaders; ++i) {
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if (lck->mti_readers[i].mr_pid) {
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/* mdbx_jitter4testing(true); */
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const pgno_t snap = lck->mti_readers[i].mr_snapshot_pages;
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if (snap && snap >= largest &&
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lck->mti_oldest >= lck->mti_readers[i].mr_txnid)
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largest = snap;
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}
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}
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}
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return largest;
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}
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/* Add a page to the txn's dirty list */
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static int __must_check_result mdbx_page_dirty(MDBX_txn *txn, MDBX_page *mp) {
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int (*const adder)(MDBX_DPL, pgno_t pgno, MDBX_page * page) =
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@ -3233,6 +3252,7 @@ static int mdbx_txn_renew0(MDBX_txn *txn, unsigned flags) {
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const txnid_t snap = mdbx_meta_txnid_fluid(env, meta);
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mdbx_jitter4testing(false);
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if (r) {
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r->mr_snapshot_pages = meta->mm_geo.next;
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r->mr_txnid = snap;
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mdbx_jitter4testing(false);
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mdbx_assert(env, r->mr_pid == mdbx_getpid());
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@ -3631,7 +3651,9 @@ static int mdbx_txn_end(MDBX_txn *txn, unsigned mode) {
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mdbx_ensure(env, /* paranoia is appropriate here */
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txn->mt_txnid == txn->mt_ro_reader->mr_txnid &&
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txn->mt_ro_reader->mr_txnid >= env->me_lck->mti_oldest);
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txn->mt_ro_reader->mr_snapshot_pages = 0;
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txn->mt_ro_reader->mr_txnid = ~(txnid_t)0;
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mdbx_memory_barrier();
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env->me_lck->mti_readers_refresh_flag = true;
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if (mode & MDBX_END_SLOT) {
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if ((env->me_flags & MDBX_ENV_TXKEY) == 0)
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@ -5321,19 +5343,23 @@ static int mdbx_sync_locked(MDBX_env *env, unsigned flags,
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if ((flags & MDBX_SHRINK_ALLOWED) && pending->mm_geo.shrink &&
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pending->mm_geo.now - pending->mm_geo.next >
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pending->mm_geo.shrink + backlog_gap) {
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const pgno_t aligner =
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pending->mm_geo.grow ? pending->mm_geo.grow : pending->mm_geo.shrink;
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const pgno_t with_backlog_gap = pending->mm_geo.next + backlog_gap;
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const pgno_t aligned = pgno_align2os_pgno(
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env, with_backlog_gap + aligner - with_backlog_gap % aligner);
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const pgno_t bottom =
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(aligned > pending->mm_geo.lower) ? aligned : pending->mm_geo.lower;
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if (pending->mm_geo.now > bottom) {
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flags &= MDBX_WRITEMAP | MDBX_SHRINK_ALLOWED; /* force steady */
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shrink = pending->mm_geo.now - bottom;
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pending->mm_geo.now = bottom;
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if (mdbx_meta_txnid_stable(env, head) == pending->mm_txnid_a)
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mdbx_meta_set_txnid(env, pending, pending->mm_txnid_a + 1);
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const pgno_t largest = mdbx_find_largest(env, pending->mm_geo.next);
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if (pending->mm_geo.now > largest &&
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pending->mm_geo.now - largest > pending->mm_geo.shrink + backlog_gap) {
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const pgno_t aligner =
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pending->mm_geo.grow ? pending->mm_geo.grow : pending->mm_geo.shrink;
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const pgno_t with_backlog_gap = largest + backlog_gap;
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const pgno_t aligned = pgno_align2os_pgno(
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env, with_backlog_gap + aligner - with_backlog_gap % aligner);
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const pgno_t bottom =
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(aligned > pending->mm_geo.lower) ? aligned : pending->mm_geo.lower;
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if (pending->mm_geo.now > bottom) {
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flags &= MDBX_WRITEMAP | MDBX_SHRINK_ALLOWED; /* force steady */
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shrink = pending->mm_geo.now - bottom;
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pending->mm_geo.now = bottom;
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if (mdbx_meta_txnid_stable(env, head) == pending->mm_txnid_a)
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mdbx_meta_set_txnid(env, pending, pending->mm_txnid_a + 1);
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}
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}
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}
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@ -11687,12 +11713,13 @@ static int __cold mdbx_env_copy_asis(MDBX_env *env, MDBX_txn *read_txn,
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}
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#else
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uint8_t *data_buffer = buffer + meta_bytes;
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for (size_t offset = meta_bytes;
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likely(rc == MDBX_SUCCESS) && offset < data_bytes;) {
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for (size_t offset = meta_bytes; offset < data_bytes;) {
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const size_t chunk =
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(MDBX_WBUF < data_bytes - offset) ? MDBX_WBUF : data_bytes - offset;
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memcpy(data_buffer, env->me_map + offset, chunk);
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rc = mdbx_pwrite(fd, data_buffer, chunk, offset);
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if (unlikely(rc != MDBX_SUCCESS))
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break;
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offset += chunk;
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}
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#endif
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