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mdbx: fix performance degradation in the absence of readers.

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Change-Id: I59a51b61918463e68d3e0490c715f4dcc9ecb788
This commit is contained in:
Leo Yuriev 2017-10-26 20:28:59 +03:00
parent f9b1bbe1e3
commit b6f14780e3
2 changed files with 47 additions and 23 deletions
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2
src/bits.h
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@ -405,7 +405,7 @@ typedef struct MDBX_lockinfo {
};
union {
volatile uint32_t mti_reader_finished_flag;
volatile uint32_t mti_readers_refresh_flag;
uint64_t align_reader_finished_flag;
};

68
src/mdbx.c
View File

@ -1556,26 +1556,51 @@ static txnid_t mdbx_find_oldest(MDBX_txn *txn) {
const MDBX_env *env = txn->mt_env;
MDBX_lockinfo *const lck = env->me_lck;
txnid_t oldest = mdbx_reclaiming_detent(env);
mdbx_tassert(txn, oldest <= txn->mt_txnid - 1);
const txnid_t edge = mdbx_reclaiming_detent(env);
mdbx_tassert(txn, edge <= txn->mt_txnid - 1);
const txnid_t last_oldest = lck->mti_oldest;
mdbx_tassert(txn, oldest >= last_oldest);
if (last_oldest == oldest ||
lck->mti_reader_finished_flag == MDBX_STRING_TETRAD("None"))
return last_oldest;
mdbx_tassert(txn, edge >= last_oldest);
if (last_oldest == edge)
return edge;
const unsigned snap_nreaders = lck->mti_numreaders;
lck->mti_reader_finished_flag = MDBX_STRING_TETRAD("None");
for (unsigned i = 0; i < snap_nreaders; ++i) {
if (lck->mti_readers[i].mr_pid) {
/* mdbx_jitter4testing(true); */
const txnid_t snap = lck->mti_readers[i].mr_txnid;
if (oldest > snap && last_oldest <= /* ignore pending updates */ snap) {
oldest = snap;
if (oldest == last_oldest)
break;
const uint32_t nothing_changed = MDBX_STRING_TETRAD("None");
const uint32_t no_readers = MDBX_STRING_TETRAD("Void");
const uint32_t snap_readers_refresh_flag = lck->mti_readers_refresh_flag;
mdbx_jitter4testing(false);
if (snap_readers_refresh_flag == nothing_changed)
return last_oldest;
if (snap_readers_refresh_flag == no_readers) {
mdbx_notice("no-reareds, update oldest %" PRIaTXN " -> %" PRIaTXN,
last_oldest, edge);
mdbx_tassert(txn, edge >= lck->mti_oldest);
return lck->mti_oldest = edge;
}
unsigned pending = 0;
txnid_t oldest = edge;
while (true) {
lck->mti_readers_refresh_flag = nothing_changed;
mdbx_coherent_barrier();
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 txnid_t snap = lck->mti_readers[i].mr_txnid;
pending += (snap < ~(txnid_t)0);
if (oldest > snap && last_oldest <= /* ignore pending updates */ snap) {
oldest = snap;
if (oldest == last_oldest)
return oldest;
}
}
}
if (unlikely(lck->mti_readers_refresh_flag != nothing_changed))
continue;
if (pending > 0 ||
mdbx_atomic_compare_and_swap32(&lck->mti_readers_refresh_flag,
nothing_changed, no_readers))
break;
}
if (oldest != last_oldest) {
@ -2529,6 +2554,7 @@ static int mdbx_txn_renew0(MDBX_txn *txn, unsigned flags) {
mdbx_assert(env, r->mr_tid == mdbx_thread_self());
mdbx_assert(env, r->mr_txnid == snap);
mdbx_coherent_barrier();
env->me_lck->mti_readers_refresh_flag = true;
}
mdbx_jitter4testing(true);
@ -2544,12 +2570,10 @@ static int mdbx_txn_renew0(MDBX_txn *txn, unsigned flags) {
mdbx_compiler_barrier();
if (likely(meta == mdbx_meta_head(env) &&
snap == mdbx_meta_txnid_fluid(env, meta) &&
snap >= env->me_oldest[0])) {
snap >= *env->me_oldest)) {
mdbx_jitter4testing(false);
break;
}
if (env->me_lck)
env->me_lck->mti_reader_finished_flag = true;
}
if (unlikely(txn->mt_txnid == 0)) {
@ -2854,7 +2878,7 @@ static int mdbx_txn_end(MDBX_txn *txn, unsigned mode) {
if (F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY)) {
if (txn->mt_ro_reader) {
txn->mt_ro_reader->mr_txnid = ~(txnid_t)0;
env->me_lck->mti_reader_finished_flag = true;
env->me_lck->mti_readers_refresh_flag = true;
if (mode & MDBX_END_SLOT) {
if ((env->me_flags & MDBX_ENV_TXKEY) == 0)
txn->mt_ro_reader->mr_pid = 0;
@ -10645,7 +10669,7 @@ int __cold mdbx_reader_check0(MDBX_env *env, int rdt_locked, int *dead) {
mdbx_debug("clear stale reader pid %" PRIuPTR " txn %" PRIaTXN "",
(size_t)pid, lck->mti_readers[j].mr_txnid);
lck->mti_readers[j].mr_pid = 0;
lck->mti_reader_finished_flag = true;
lck->mti_readers_refresh_flag = true;
count++;
}
}
@ -10754,7 +10778,7 @@ static txnid_t __cold mdbx_oomkick(MDBX_env *env, const txnid_t laggard) {
if (rc) {
asleep->mr_txnid = ~(txnid_t)0;
env->me_lck->mti_reader_finished_flag = true;
env->me_lck->mti_readers_refresh_flag = true;
if (rc > 1) {
asleep->mr_tid = 0;
asleep->mr_pid = 0;