[Tarantool-patches] [PATCH 4/5] [tosquash] replication: rework how local transactions wait sync
Serge Petrenko
sergepetrenko at tarantool.org
Sun Jul 5 12:04:05 MSK 2020
03.07.2020 02:40, Vladislav Shpilevoy пишет:
> There was a bug about how async transactions were blocked by a
> not empty limbo. This was about fully local transactions. The
> problem is that they don't have LSN in the needed vclock
> component - it is always 0. It means, that their limbo entry
> can't get a valid LSN by any means. Even a copy of the previous
> sync transaction's LSN won't work, because the latter may by
> still not written to WAL.
>
> This patch makes async transactions always have lsn -1 in their
> limbo entry. Because anyway it does not matter. It is not needed
> to collect ACKs, nor to propagate limbo's vclock.
>
> Now even a fully local transaction can be blocked by a pending
> sync transaction.
>
> Note, this does not cover the case, when the transaction is not
> fully local, and its last row is local.
Hi! Thanks for the patch! Looks good, with one comment below.
> ---
> src/box/txn.c | 18 ++--
> src/box/txn_limbo.c | 60 +++++++------
> test/replication/qsync_basic.result | 120 ++++++++++++++++++++++++++
> test/replication/qsync_basic.test.lua | 45 ++++++++++
> 4 files changed, 208 insertions(+), 35 deletions(-)
>
> diff --git a/src/box/txn.c b/src/box/txn.c
> index 6c333cbed..fe0591197 100644
> --- a/src/box/txn.c
> +++ b/src/box/txn.c
> @@ -688,15 +688,15 @@ txn_commit_async(struct txn *txn)
>
> /* See txn_commit(). */
> uint32_t origin_id = req->rows[0]->replica_id;
> - int64_t lsn = req->rows[txn->n_applier_rows - 1]->lsn;
> limbo_entry = txn_limbo_append(&txn_limbo, origin_id, txn);
> if (limbo_entry == NULL) {
> txn_rollback(txn);
> return -1;
> }
> - assert(lsn > 0);
> - txn_limbo_assign_lsn(&txn_limbo, limbo_entry, lsn);
> -
> + if (txn_has_flag(txn, TXN_WAIT_ACK)) {
> + int64_t lsn = req->rows[txn->n_applier_rows - 1]->lsn;
> + txn_limbo_assign_lsn(&txn_limbo, limbo_entry, lsn);
> + }
> /*
> * Set a trigger to abort waiting for confirm on
> * WAL write failure.
> @@ -779,10 +779,12 @@ txn_commit(struct txn *txn)
> return -1;
> }
> if (is_sync) {
> - int64_t lsn = req->rows[req->n_rows - 1]->lsn;
> - txn_limbo_assign_lsn(&txn_limbo, limbo_entry, lsn);
> - /* Local WAL write is a first 'ACK'. */
> - txn_limbo_ack(&txn_limbo, txn_limbo.instance_id, lsn);
> + if (txn_has_flag(txn, TXN_WAIT_ACK)) {
> + int64_t lsn = req->rows[req->n_rows - 1]->lsn;
> + txn_limbo_assign_lsn(&txn_limbo, limbo_entry, lsn);
> + /* Local WAL write is a first 'ACK'. */
> + txn_limbo_ack(&txn_limbo, txn_limbo.instance_id, lsn);
> + }
> if (txn_limbo_wait_complete(&txn_limbo, limbo_entry) < 0) {
> txn_free(txn);
> return -1;
> diff --git a/src/box/txn_limbo.c b/src/box/txn_limbo.c
> index 387cfd337..44a0c7273 100644
> --- a/src/box/txn_limbo.c
> +++ b/src/box/txn_limbo.c
> @@ -120,6 +120,7 @@ txn_limbo_assign_lsn(struct txn_limbo *limbo, struct txn_limbo_entry *entry,
> assert(limbo->instance_id != REPLICA_ID_NIL);
> assert(entry->lsn == -1);
> assert(lsn > 0);
> + assert(txn_has_flag(entry->txn, TXN_WAIT_ACK));
> (void) limbo;
> entry->lsn = lsn;
> }
> @@ -129,6 +130,12 @@ txn_limbo_check_complete(struct txn_limbo *limbo, struct txn_limbo_entry *entry)
> {
> if (txn_limbo_entry_is_complete(entry))
> return true;
> + /*
> + * Async transaction can't complete itself. It is always
> + * completed by a previous sync transaction.
> + */
> + if (!txn_has_flag(entry->txn, TXN_WAIT_ACK))
> + return false;
> struct vclock_iterator iter;
> vclock_iterator_init(&iter, &limbo->vclock);
> int ack_count = 0;
> @@ -142,14 +149,13 @@ txn_limbo_check_complete(struct txn_limbo *limbo, struct txn_limbo_entry *entry)
> }
>
> static int
> -txn_limbo_write_rollback(struct txn_limbo *limbo,
> - struct txn_limbo_entry *entry);
> +txn_limbo_write_rollback(struct txn_limbo *limbo, int64_t lsn);
>
> int
> txn_limbo_wait_complete(struct txn_limbo *limbo, struct txn_limbo_entry *entry)
> {
> struct txn *txn = entry->txn;
> - assert(entry->lsn > 0);
> + assert(entry->lsn > 0 || !txn_has_flag(entry->txn, TXN_WAIT_ACK));
> assert(!txn_has_flag(txn, TXN_IS_DONE));
> assert(txn_has_flag(txn, TXN_WAIT_SYNC));
> if (txn_limbo_check_complete(limbo, entry))
> @@ -176,7 +182,7 @@ txn_limbo_wait_complete(struct txn_limbo *limbo, struct txn_limbo_entry *entry)
> goto complete;
> }
>
> - txn_limbo_write_rollback(limbo, entry);
> + txn_limbo_write_rollback(limbo, entry->lsn);
> struct txn_limbo_entry *e, *tmp;
> rlist_foreach_entry_safe_reverse(e, &limbo->queue,
> in_queue, tmp) {
> @@ -210,10 +216,11 @@ complete:
> }
>
> static int
> -txn_limbo_write_confirm_rollback(struct txn_limbo *limbo,
> - struct txn_limbo_entry *entry,
> +txn_limbo_write_confirm_rollback(struct txn_limbo *limbo, int64_t lsn,
> bool is_confirm)
> {
> + assert(lsn > 0);
> +
> struct xrow_header row;
> struct request request = {
> .header = &row,
> @@ -221,14 +228,13 @@ txn_limbo_write_confirm_rollback(struct txn_limbo *limbo,
>
> int res = 0;
> if (is_confirm) {
> - res = xrow_encode_confirm(&row, limbo->instance_id, entry->lsn);
> + res = xrow_encode_confirm(&row, limbo->instance_id, lsn);
> } else {
> /*
> * This entry is the first to be rolled back, so
> - * the last "safe" lsn is entry->lsn - 1.
> + * the last "safe" lsn is lsn - 1.
> */
> - res = xrow_encode_rollback(&row, limbo->instance_id,
> - entry->lsn - 1);
> + res = xrow_encode_rollback(&row, limbo->instance_id, lsn - 1);
> }
> if (res == -1)
> return -1;
> @@ -260,10 +266,9 @@ rollback:
> * transactions waiting for confirmation may be finished.
> */
> static int
> -txn_limbo_write_confirm(struct txn_limbo *limbo,
> - struct txn_limbo_entry *entry)
> +txn_limbo_write_confirm(struct txn_limbo *limbo, int64_t lsn)
> {
> - return txn_limbo_write_confirm_rollback(limbo, entry, true);
> + return txn_limbo_write_confirm_rollback(limbo, lsn, true);
> }
>
> void
> @@ -300,14 +305,13 @@ txn_limbo_read_confirm(struct txn_limbo *limbo, int64_t lsn)
>
> /**
> * Write a rollback message to WAL. After it's written
> - * all the tarnsactions following the current one and waiting
> + * all the transactions following the current one and waiting
> * for confirmation must be rolled back.
> */
> static int
> -txn_limbo_write_rollback(struct txn_limbo *limbo,
> - struct txn_limbo_entry *entry)
> +txn_limbo_write_rollback(struct txn_limbo *limbo, int64_t lsn)
> {
> - return txn_limbo_write_confirm_rollback(limbo, entry, false);
> + return txn_limbo_write_confirm_rollback(limbo, lsn, false);
> }
>
> void
> @@ -316,7 +320,7 @@ txn_limbo_read_rollback(struct txn_limbo *limbo, int64_t lsn)
> assert(limbo->instance_id != REPLICA_ID_NIL);
> struct txn_limbo_entry *e, *tmp;
> rlist_foreach_entry_safe_reverse(e, &limbo->queue, in_queue, tmp) {
> - if (e->lsn <= lsn)
> + if (e->lsn <= lsn && txn_has_flag(e->txn, TXN_WAIT_ACK))
> break;
Are you rolling back the async transactions that are before the last sync
transaction to be rolled back? Why?
Shouldn't this condition stay the same?
> e->is_rollback = true;
> txn_limbo_pop(limbo, e);
> @@ -350,31 +354,33 @@ txn_limbo_ack(struct txn_limbo *limbo, uint32_t replica_id, int64_t lsn)
> int64_t prev_lsn = vclock_get(&limbo->vclock, replica_id);
> vclock_follow(&limbo->vclock, replica_id, lsn);
> struct txn_limbo_entry *e, *last_quorum = NULL;
> + int64_t confirm_lsn = -1;
> rlist_foreach_entry(e, &limbo->queue, in_queue) {
> + assert(e->ack_count <= VCLOCK_MAX);
> if (e->lsn > lsn)
> break;
> - if (e->lsn <= prev_lsn)
> - continue;
> - assert(e->ack_count <= VCLOCK_MAX);
> /*
> * Sync transactions need to collect acks. Async
> * transactions are automatically committed right
> * after all the previous sync transactions are.
> */
> - if (txn_has_flag(e->txn, TXN_WAIT_ACK)) {
> - if (++e->ack_count < replication_synchro_quorum)
> - continue;
> - } else {
> - assert(txn_has_flag(e->txn, TXN_WAIT_SYNC));
> + if (!txn_has_flag(e->txn, TXN_WAIT_ACK)) {
> + assert(e->lsn == -1);
> if (last_quorum == NULL)
> continue;
> + } else if (e->lsn <= prev_lsn) {
> + continue;
> + } else if (++e->ack_count < replication_synchro_quorum) {
> + continue;
> + } else {
> + confirm_lsn = e->lsn;
> }
> e->is_commit = true;
> last_quorum = e;
> }
> if (last_quorum == NULL)
> return;
> - if (txn_limbo_write_confirm(limbo, last_quorum) != 0) {
> + if (txn_limbo_write_confirm(limbo, confirm_lsn) != 0) {
> // TODO: what to do here?.
> // We already failed writing the CONFIRM
> // message. What are the chances we'll be
> diff --git a/test/replication/qsync_basic.result b/test/replication/qsync_basic.result
> index 32deb2ac3..339fc0e33 100644
> --- a/test/replication/qsync_basic.result
> +++ b/test/replication/qsync_basic.result
> @@ -299,6 +299,126 @@ box.space.sync:select{6}
> | - []
> | ...
>
> +--
> +-- Fully local async transaction also waits for existing sync txn.
> +--
> +test_run:switch('default')
> + | ---
> + | - true
> + | ...
> +box.cfg{replication_synchro_timeout = 1000, replication_synchro_quorum = 2}
> + | ---
> + | ...
> +_ = box.schema.create_space('locallocal', {is_local = true})
> + | ---
> + | ...
> +_ = _:create_index('pk')
> + | ---
> + | ...
> +-- Propagate local vclock to some insane value to ensure it won't
> +-- affect anything.
> +box.begin() for i = 1, 2000 do box.space.locallocal:replace{1} end box.commit()
> + | ---
> + | ...
> +do \
> + f1 = fiber.create(box.space.sync.replace, box.space.sync, {8}) \
> + f2 = fiber.create(box.space.locallocal.replace, box.space.locallocal, {8}) \
> + box.space.test:replace{8} \
> +end
> + | ---
> + | ...
> +f1:status()
> + | ---
> + | - dead
> + | ...
> +f2:status()
> + | ---
> + | - dead
> + | ...
> +box.space.sync:select{8}
> + | ---
> + | - - [8]
> + | ...
> +box.space.locallocal:select{8}
> + | ---
> + | - - [8]
> + | ...
> +box.space.test:select{8}
> + | ---
> + | - - [8]
> + | ...
> +
> +test_run:switch('replica')
> + | ---
> + | - true
> + | ...
> +box.space.sync:select{8}
> + | ---
> + | - - [8]
> + | ...
> +box.space.locallocal:select{8}
> + | ---
> + | - []
> + | ...
> +box.space.test:select{8}
> + | ---
> + | - - [8]
> + | ...
> +
> +-- Ensure sync rollback will affect all pending fully local async
> +-- transactions too.
> +test_run:switch('default')
> + | ---
> + | - true
> + | ...
> +box.cfg{replication_synchro_timeout = 0.001, replication_synchro_quorum = 3}
> + | ---
> + | ...
> +do \
> + f1 = fiber.create(box.space.sync.replace, box.space.sync, {9}) \
> + f2 = fiber.create(box.space.locallocal.replace, box.space.locallocal, {9}) \
> + box.space.test:replace{9} \
> +end
> + | ---
> + | - error: A rollback for a synchronous transaction is received
> + | ...
> +f1:status()
> + | ---
> + | - dead
> + | ...
> +f2:status()
> + | ---
> + | - dead
> + | ...
> +box.space.sync:select{9}
> + | ---
> + | - []
> + | ...
> +box.space.locallocal:select{9}
> + | ---
> + | - []
> + | ...
> +box.space.test:select{9}
> + | ---
> + | - []
> + | ...
> +test_run:switch('replica')
> + | ---
> + | - true
> + | ...
> +box.space.sync:select{9}
> + | ---
> + | - []
> + | ...
> +box.space.locallocal:select{9}
> + | ---
> + | - []
> + | ...
> +box.space.test:select{9}
> + | ---
> + | - []
> + | ...
> +
> --
> -- gh-5123: quorum 1 still should write CONFIRM.
> --
> diff --git a/test/replication/qsync_basic.test.lua b/test/replication/qsync_basic.test.lua
> index 361f22bc3..6e40131bf 100644
> --- a/test/replication/qsync_basic.test.lua
> +++ b/test/replication/qsync_basic.test.lua
> @@ -118,6 +118,51 @@ test_run:switch('replica')
> box.space.test:select{6}
> box.space.sync:select{6}
>
> +--
> +-- Fully local async transaction also waits for existing sync txn.
> +--
> +test_run:switch('default')
> +box.cfg{replication_synchro_timeout = 1000, replication_synchro_quorum = 2}
> +_ = box.schema.create_space('locallocal', {is_local = true})
> +_ = _:create_index('pk')
> +-- Propagate local vclock to some insane value to ensure it won't
> +-- affect anything.
> +box.begin() for i = 1, 2000 do box.space.locallocal:replace{1} end box.commit()
> +do \
> + f1 = fiber.create(box.space.sync.replace, box.space.sync, {8}) \
> + f2 = fiber.create(box.space.locallocal.replace, box.space.locallocal, {8}) \
> + box.space.test:replace{8} \
> +end
> +f1:status()
> +f2:status()
> +box.space.sync:select{8}
> +box.space.locallocal:select{8}
> +box.space.test:select{8}
> +
> +test_run:switch('replica')
> +box.space.sync:select{8}
> +box.space.locallocal:select{8}
> +box.space.test:select{8}
> +
> +-- Ensure sync rollback will affect all pending fully local async
> +-- transactions too.
> +test_run:switch('default')
> +box.cfg{replication_synchro_timeout = 0.001, replication_synchro_quorum = 3}
> +do \
> + f1 = fiber.create(box.space.sync.replace, box.space.sync, {9}) \
> + f2 = fiber.create(box.space.locallocal.replace, box.space.locallocal, {9}) \
> + box.space.test:replace{9} \
> +end
> +f1:status()
> +f2:status()
> +box.space.sync:select{9}
> +box.space.locallocal:select{9}
> +box.space.test:select{9}
> +test_run:switch('replica')
> +box.space.sync:select{9}
> +box.space.locallocal:select{9}
> +box.space.test:select{9}
> +
> --
> -- gh-5123: quorum 1 still should write CONFIRM.
> --
--
Serge Petrenko
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