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mdbx: fix DB-shrinking race with copy-asis & readers.

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Change-Id: I1e05616de03d814850a1c8ad20e83941b2d1c911
This commit is contained in:
Leonid Yuriev
2019-07-09 00:29:59 +03:00
parent bd5078347b
commit 53563e75bb
2 changed files with 49 additions and 19 deletions
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9
src/bits.h
View File

@@ -259,11 +259,14 @@ typedef struct MDBX_reader {
volatile mdbx_pid_t mr_pid;
/* The thread ID of the thread owning this txn. */
volatile mdbx_tid_t mr_tid;
/* The number of pages used in the reader's MVCC snapshot,
* i.e. the value of meta->mm_geo.next and txn->mt_next_pgno */
volatile pgno_t mr_snapshot_pages;
/* cache line alignment */
uint8_t pad[MDBX_CACHELINE_SIZE -
(sizeof(txnid_t) + sizeof(mdbx_pid_t) + sizeof(mdbx_tid_t)) %
MDBX_CACHELINE_SIZE];
uint8_t pad[MDBX_CACHELINE_SIZE - (sizeof(txnid_t) + sizeof(mdbx_pid_t) +
sizeof(mdbx_tid_t) + sizeof(pgno_t)) %
MDBX_CACHELINE_SIZE];
} MDBX_reader;
/* Information about a single database in the environment. */

59
src/mdbx.c
View File

@@ -2163,7 +2163,7 @@ static txnid_t mdbx_find_oldest(MDBX_txn *txn) {
mdbx_tassert(txn, edge <= txn->mt_txnid - 1);
MDBX_lockinfo *const lck = env->me_lck;
if (unlikely(env->me_lck == NULL /* exclusive mode */))
if (unlikely(lck == NULL /* exclusive mode */))
return env->me_oldest_stub = edge;
const txnid_t last_oldest = lck->mti_oldest;
@@ -2201,6 +2201,25 @@ static txnid_t mdbx_find_oldest(MDBX_txn *txn) {
return oldest;
}
/* Find largest mvcc-snapshot still referenced. */
static pgno_t mdbx_find_largest(MDBX_env *env, pgno_t largest) {
MDBX_lockinfo *const lck = env->me_lck;
if (likely(lck != NULL /* exclusive mode */)) {
const unsigned snap_nreaders = lck->mti_numreaders;
for (unsigned i = 0; i < snap_nreaders; ++i) {
if (lck->mti_readers[i].mr_pid) {
/* mdbx_jitter4testing(true); */
const pgno_t snap = lck->mti_readers[i].mr_snapshot_pages;
if (snap && snap >= largest &&
lck->mti_oldest >= lck->mti_readers[i].mr_txnid)
largest = snap;
}
}
}
return largest;
}
/* Add a page to the txn's dirty list */
static int __must_check_result mdbx_page_dirty(MDBX_txn *txn, MDBX_page *mp) {
int (*const adder)(MDBX_DPL, pgno_t pgno, MDBX_page * page) =
@@ -3233,6 +3252,7 @@ static int mdbx_txn_renew0(MDBX_txn *txn, unsigned flags) {
const txnid_t snap = mdbx_meta_txnid_fluid(env, meta);
mdbx_jitter4testing(false);
if (r) {
r->mr_snapshot_pages = meta->mm_geo.next;
r->mr_txnid = snap;
mdbx_jitter4testing(false);
mdbx_assert(env, r->mr_pid == mdbx_getpid());
@@ -3631,7 +3651,9 @@ static int mdbx_txn_end(MDBX_txn *txn, unsigned mode) {
mdbx_ensure(env, /* paranoia is appropriate here */
txn->mt_txnid == txn->mt_ro_reader->mr_txnid &&
txn->mt_ro_reader->mr_txnid >= env->me_lck->mti_oldest);
txn->mt_ro_reader->mr_snapshot_pages = 0;
txn->mt_ro_reader->mr_txnid = ~(txnid_t)0;
mdbx_memory_barrier();
env->me_lck->mti_readers_refresh_flag = true;
if (mode & MDBX_END_SLOT) {
if ((env->me_flags & MDBX_ENV_TXKEY) == 0)
@@ -5321,19 +5343,23 @@ static int mdbx_sync_locked(MDBX_env *env, unsigned flags,
if ((flags & MDBX_SHRINK_ALLOWED) && pending->mm_geo.shrink &&
pending->mm_geo.now - pending->mm_geo.next >
pending->mm_geo.shrink + backlog_gap) {
const pgno_t aligner =
pending->mm_geo.grow ? pending->mm_geo.grow : pending->mm_geo.shrink;
const pgno_t with_backlog_gap = pending->mm_geo.next + backlog_gap;
const pgno_t aligned = pgno_align2os_pgno(
env, with_backlog_gap + aligner - with_backlog_gap % aligner);
const pgno_t bottom =
(aligned > pending->mm_geo.lower) ? aligned : pending->mm_geo.lower;
if (pending->mm_geo.now > bottom) {
flags &= MDBX_WRITEMAP | MDBX_SHRINK_ALLOWED; /* force steady */
shrink = pending->mm_geo.now - bottom;
pending->mm_geo.now = bottom;
if (mdbx_meta_txnid_stable(env, head) == pending->mm_txnid_a)
mdbx_meta_set_txnid(env, pending, pending->mm_txnid_a + 1);
const pgno_t largest = mdbx_find_largest(env, pending->mm_geo.next);
if (pending->mm_geo.now > largest &&
pending->mm_geo.now - largest > pending->mm_geo.shrink + backlog_gap) {
const pgno_t aligner =
pending->mm_geo.grow ? pending->mm_geo.grow : pending->mm_geo.shrink;
const pgno_t with_backlog_gap = largest + backlog_gap;
const pgno_t aligned = pgno_align2os_pgno(
env, with_backlog_gap + aligner - with_backlog_gap % aligner);
const pgno_t bottom =
(aligned > pending->mm_geo.lower) ? aligned : pending->mm_geo.lower;
if (pending->mm_geo.now > bottom) {
flags &= MDBX_WRITEMAP | MDBX_SHRINK_ALLOWED; /* force steady */
shrink = pending->mm_geo.now - bottom;
pending->mm_geo.now = bottom;
if (mdbx_meta_txnid_stable(env, head) == pending->mm_txnid_a)
mdbx_meta_set_txnid(env, pending, pending->mm_txnid_a + 1);
}
}
}
@@ -11687,12 +11713,13 @@ static int __cold mdbx_env_copy_asis(MDBX_env *env, MDBX_txn *read_txn,
}
#else
uint8_t *data_buffer = buffer + meta_bytes;
for (size_t offset = meta_bytes;
likely(rc == MDBX_SUCCESS) && offset < data_bytes;) {
for (size_t offset = meta_bytes; offset < data_bytes;) {
const size_t chunk =
(MDBX_WBUF < data_bytes - offset) ? MDBX_WBUF : data_bytes - offset;
memcpy(data_buffer, env->me_map + offset, chunk);
rc = mdbx_pwrite(fd, data_buffer, chunk, offset);
if (unlikely(rc != MDBX_SUCCESS))
break;
offset += chunk;
}
#endif