On 4/26/22 03:08, Han Zhou wrote: > On Wed, Apr 20, 2022 at 12:31 PM Dumitru Ceara <dce...@redhat.com> wrote: >> >> At a first glance, change tracking should never be allowed for >> write-only columns. However, some clients (e.g., ovn-northd) that are >> mostly exclusive writers of a database, use change tracking to avoid >> duplicating the IDL row records into a local cache when implementing >> incremental processing. >> >> The default behavior of the IDL is to automatically turn a write-only >> column into a read-write column whenever the client enables change >> tracking for that column. >> >> For the afore mentioned clients, this becomes a performance issue. >> Commit 1cc618c32524 ("ovsdb-idl: Fix atomicity of writes that don't >> change a column's value.") explains why writes that don't change a >> column's value cannot be optimized out early if the column is >> read/write. >> >> Furthermore, if there is at least one record in any table that >> changed during a transaction, then *all* records that have been >> written are added to the transaction, even if their values didn't >> change. If there are many such rows (e.g., like in ovn-northd's >> case) this incurs a significant overhead because: >> a. the client has to build this large transaction >> b. the transaction has to be sent over the network >> c. the server needs to parse this (mostly) no-op update >> >> We now introduce new IDL APIs allowing users to set a new monitoring >> mode flag, OVSDB_IDL_WRITE_CHANGED_ONLY, to indicate to the IDL that the >> atomicity constraints may be relaxed and written columns that don't >> change value can be skipped from the current transaction. >> >> We benchmarked ovn-northd performance when using this new mode >> against NB and SB databases taken from ovn-kubernetes scale tests. >> We noticed that when a minor change is performed to the Northbound >> database (e.g., NB_Global.nb_cfg is incremented) the time it takes to >> build the Southbound transaction becomes negligible (vs ~1.5 seconds >> before this change). >> >> End-to-end ovn-kubernetes scale tests on 120-node clusters also show >> significant reduction of latency to bring up pods; both average and P99 >> latency decreased by ~30%. >> >> Signed-off-by: Dumitru Ceara <dce...@redhat.com> > > Thanks Dumitru for the revision. I only have two minor comments below. > > Acked-by: Han Zhou <hz...@ovn.org> > >> --- >> V3: >> - Addressed Han's comments: >> - Add a new IDL monitor mode flag, OVSDB_IDL_WRITE_CHANGED_ONLY. >> - Rephrased commit log. >> - Changed commit title to reflect the new approach. >> - Old patch (v2) was: >> > https://patchwork.ozlabs.org/project/openvswitch/patch/20220415142146.13169-1-dce...@redhat.com/ >> V2: >> - Addressed Numan's comments: >> - Added APIs to allow per column configuration of modes. >> - Fixed unit tests to actually enable change tracking for write-only >> columns. >> - Fixed ovsdb_idl_row_change() to correctly update row/table/idl change >> seqnos if change tracking is enabled (even for write-only rows). >> >> Note: The OVN counter part change is: >> > https://github.com/dceara/ovn/commit/5afba6f3aa51f508df41d8f0b7b9d739b00b1ee2 >> --- >> NEWS | 4 ++++ >> lib/ovsdb-idl.c | 57 +++++++++++++++++++++++++++++++++++++++++----- >> lib/ovsdb-idl.h | 14 +++++++++++- >> tests/ovsdb-idl.at | 31 ++++++++++++++++++++++++- >> tests/test-ovsdb.c | 18 +++++++++++---- >> 5 files changed, 111 insertions(+), 13 deletions(-) >> >> diff --git a/NEWS b/NEWS >> index 5074b97aa51c..60932791bfcf 100644 >> --- a/NEWS >> +++ b/NEWS >> @@ -14,6 +14,10 @@ Post-v2.17.0 >> - OVSDB: >> * 'relay' service model now supports transaction history, i.e. > honors the >> 'last-txn-id' field in 'monitor_cond_since' requests from clients. >> + - OVSDB-IDL: >> + * New monitor mode flag, OVSDB_IDL_WRITE_CHANGED_ONLY, allowing >> + applications to relax atomicity requirements when dealing with >> + columns whose value has been rewritten (but not changed). >> >> >> v2.17.0 - 17 Feb 2022 >> diff --git a/lib/ovsdb-idl.c b/lib/ovsdb-idl.c >> index 882ede75598d..e5bb6cca5274 100644 >> --- a/lib/ovsdb-idl.c >> +++ b/lib/ovsdb-idl.c >> @@ -1396,6 +1396,42 @@ ovsdb_idl_track_clear(struct ovsdb_idl *idl) >> { >> ovsdb_idl_track_clear__(idl, false); >> } >> + >> +/* Sets or clears (depending on 'enable') OVSDB_IDL_WRITE_CHANGED_ONLY >> + * for 'column' in 'idl', ensuring that the column will be included in a >> + * transaction only if its value has actually changed locally. Normally >> + * read/write columns that are written to are always included in the >> + * transaction but, in specific cases, when the application doesn't >> + * require atomicity of writes across different columns the ones that >> + * don't chave value may be skipped. > > s/chave/change >
Ack. >> + * >> + * This function should be called between ovsdb_idl_create() and >> + * the first call to ovsdb_idl_run(). >> + */ >> +void >> +ovsdb_idl_set_write_change_only(struct ovsdb_idl *idl, >> + const struct ovsdb_idl_column *column, >> + bool enable) >> +{ >> + if (enable) { >> + *ovsdb_idl_get_mode(idl, column) |= OVSDB_IDL_WRITE_CHANGED_ONLY; >> + } else { >> + *ovsdb_idl_get_mode(idl, column) &= > ~OVSDB_IDL_WRITE_CHANGED_ONLY; >> + } >> +} >> + >> +void >> +ovsdb_idl_set_write_change_only_all(struct ovsdb_idl *idl, bool enable) >> +{ >> + for (size_t i = 0; i < idl->class_->n_tables; i++) { >> + const struct ovsdb_idl_table_class *tc = &idl->class_->tables[i]; >> + >> + for (size_t j = 0; j < tc->n_columns; j++) { >> + const struct ovsdb_idl_column *column = &tc->columns[j]; >> + ovsdb_idl_set_write_change_only(idl, column, enable); >> + } >> + } >> +} >> >> static void >> log_parse_update_error(struct ovsdb_error *error) >> @@ -3491,6 +3527,8 @@ ovsdb_idl_txn_write__(const struct ovsdb_idl_row > *row_, >> { >> struct ovsdb_idl_row *row = CONST_CAST(struct ovsdb_idl_row *, row_); >> const struct ovsdb_idl_table_class *class; >> + unsigned char column_mode; >> + bool optimize_rewritten; >> size_t column_idx; >> bool write_only; >> >> @@ -3501,12 +3539,15 @@ ovsdb_idl_txn_write__(const struct ovsdb_idl_row > *row_, >> >> class = row->table->class_; >> column_idx = column - class->columns; >> - write_only = row->table->modes[column_idx] == OVSDB_IDL_MONITOR; >> + column_mode = row->table->modes[column_idx]; >> + write_only = column_mode == OVSDB_IDL_MONITOR; >> + optimize_rewritten = >> + write_only || (column_mode & OVSDB_IDL_WRITE_CHANGED_ONLY); >> + >> >> ovs_assert(row->new_datum != NULL); >> ovs_assert(column_idx < class->n_columns); >> - ovs_assert(row->old_datum == NULL || >> - row->table->modes[column_idx] & OVSDB_IDL_MONITOR); >> + ovs_assert(row->old_datum == NULL || column_mode & > OVSDB_IDL_MONITOR); >> >> if (row->table->idl->verify_write_only && !write_only) { >> VLOG_ERR("Bug: Attempt to write to a read/write column (%s:%s) > when" >> @@ -3524,9 +3565,13 @@ ovsdb_idl_txn_write__(const struct ovsdb_idl_row > *row_, >> * different value in that column since we read it. (But if a whole >> * transaction only does writes of existing values, without making > any real >> * changes, we will drop the whole transaction later in >> - * ovsdb_idl_txn_commit().) */ >> - if (write_only && ovsdb_datum_equals(ovsdb_idl_read(row, column), >> - datum, &column->type)) { >> + * ovsdb_idl_txn_commit().) >> + * >> + * The application may choose to bypass this restriction and always >> + * optimize by setting OVSDB_IDL_WRITE_CHANGED_ONLY. >> + */ >> + if (optimize_rewritten && ovsdb_datum_equals(ovsdb_idl_read(row, > column), >> + datum, &column->type)) { >> goto discard_datum; >> } >> >> diff --git a/lib/ovsdb-idl.h b/lib/ovsdb-idl.h >> index d00599616ef9..1716955ab61c 100644 >> --- a/lib/ovsdb-idl.h >> +++ b/lib/ovsdb-idl.h >> @@ -181,10 +181,17 @@ bool ovsdb_idl_server_has_column(const struct > ovsdb_idl *, >> * - (OVSDB_IDL_MONITOR | OVSDB_IDL_ALERT | OVSDB_IDL_TRACK), for a > column >> * that a client wants to track using the change tracking >> * ovsdb_idl_track_get_*() functions. >> + * >> + * - (OVSDB_IDL_MONITOR | OVSDB_IDL_ALERT | > OVSDB_IDL_WRITE_CHANGED_ONLY) >> + * is similar to (OVSDB_IDL_MONITOR | OVSDB_IDL_ALERT) except that it >> + * only adds a written column to a transaction if the column's value >> + * has actually changed. > > In the original form of this comment, we need to mention "OVSDB_IDL_MONITOR > | OVSDB_IDL_ALERT | OVSDB_IDL_TRACK | OVSDB_IDL_WRITE_CHANGED_ONLY" as > well, but I think it is too tedious. Maybe we can change the section from > "possible mode combinations" to "typical mode combinations". > > I'll change this in v4. Thanks! Dumitru > >> */ >> #define OVSDB_IDL_MONITOR (1 << 0) /* Replicate this column? */ >> #define OVSDB_IDL_ALERT (1 << 1) /* Alert client when column changes? > */ >> -#define OVSDB_IDL_TRACK (1 << 2) >> +#define OVSDB_IDL_TRACK (1 << 2) /* Track column changes? */ >> +#define OVSDB_IDL_WRITE_CHANGED_ONLY \ >> + (1 << 3) /* Write back only changed columns? */ >> >> void ovsdb_idl_add_column(struct ovsdb_idl *, const struct > ovsdb_idl_column *); >> void ovsdb_idl_add_table(struct ovsdb_idl *, >> @@ -233,6 +240,11 @@ bool ovsdb_idl_track_is_updated(const struct > ovsdb_idl_row *row, >> const struct ovsdb_idl_column *column); >> void ovsdb_idl_track_clear(struct ovsdb_idl *); >> >> +void ovsdb_idl_set_write_change_only(struct ovsdb_idl *idl, >> + const struct ovsdb_idl_column > *column, >> + bool enable); >> +void ovsdb_idl_set_write_change_only_all(struct ovsdb_idl *idl, bool > enable); >> + >> >> /* Reading the database replica. */ >> >> diff --git a/tests/ovsdb-idl.at b/tests/ovsdb-idl.at >> index 62e2b638320c..d1cfa59c5758 100644 >> --- a/tests/ovsdb-idl.at >> +++ b/tests/ovsdb-idl.at >> @@ -87,6 +87,20 @@ m4_define([OVSDB_CHECK_IDL_C], >> OVSDB_SERVER_SHUTDOWN >> AT_CLEANUP]) >> >> +# same as OVSDB_CHECK_IDL but uses OVSDB_IDL_WRITE_CHANGED_ONLY. >> +m4_define([OVSDB_CHECK_IDL_WRITE_CHANGED_ONLY_C], >> + [AT_SETUP([$1 - write-changed-only - C]) >> + AT_KEYWORDS([ovsdb server idl positive $5]) >> + AT_CHECK([ovsdb_start_idltest]) >> + m4_if([$2], [], [], >> + [AT_CHECK([ovsdb-client transact unix:socket $2], [0], [ignore], > [ignore])]) >> + AT_CHECK([test-ovsdb '-vPATTERN:console:test-ovsdb|%c|%m' -vjsonrpc > -t10 idl unix:socket $3], >> + [0], [stdout], [ignore]) >> + AT_CHECK([sort stdout | uuidfilt]m4_if([$6],,, [[| $6]]), >> + [0], [$4]) >> + OVSDB_SERVER_SHUTDOWN >> + AT_CLEANUP]) >> + >> # same as OVSDB_CHECK_IDL but uses tcp. >> m4_define([OVSDB_CHECK_IDL_TCP_C], >> [AT_SETUP([$1 - C - tcp]) >> @@ -257,6 +271,7 @@ m4_define([OVSDB_CHECK_IDL_SSL_PY], >> >> m4_define([OVSDB_CHECK_IDL], >> [OVSDB_CHECK_IDL_C($@) >> + OVSDB_CHECK_IDL_WRITE_CHANGED_ONLY_C($@) >> OVSDB_CHECK_IDL_TCP_C($@) >> OVSDB_CHECK_IDL_TCP6_C($@) >> OVSDB_CHECK_IDL_PY($@) >> @@ -1166,8 +1181,22 @@ m4_define([OVSDB_CHECK_IDL_TRACK_C], >> OVSDB_SERVER_SHUTDOWN >> AT_CLEANUP]) >> >> +m4_define([OVSDB_CHECK_IDL_TRACK_WRITE_CHANGED_ONLY_C], >> + [AT_SETUP([$1 - write-changed-only - C]) >> + AT_KEYWORDS([ovsdb server idl tracking positive $5]) >> + AT_CHECK([ovsdb_start_idltest]) >> + m4_if([$2], [], [], >> + [AT_CHECK([ovsdb-client transact unix:socket $2], [0], [ignore], > [ignore])]) >> + AT_CHECK([test-ovsdb '-vPATTERN:console:test-ovsdb|%c|%m' -vjsonrpc > -t10 -c -w idl unix:socket $3], >> + [0], [stdout], [ignore]) >> + AT_CHECK([sort stdout | uuidfilt]m4_if([$6],,, [[| $6]]), >> + [0], [$4]) >> + OVSDB_SERVER_SHUTDOWN >> + AT_CLEANUP]) >> + >> m4_define([OVSDB_CHECK_IDL_TRACK], >> - [OVSDB_CHECK_IDL_TRACK_C($@)]) >> + [OVSDB_CHECK_IDL_TRACK_C($@) >> + OVSDB_CHECK_IDL_TRACK_WRITE_CHANGED_ONLY_C($@)]) >> >> OVSDB_CHECK_IDL_TRACK([track, simple idl, initially populated], >> [['["idltest", >> diff --git a/tests/test-ovsdb.c b/tests/test-ovsdb.c >> index ca4e87b8115c..808b15355743 100644 >> --- a/tests/test-ovsdb.c >> +++ b/tests/test-ovsdb.c >> @@ -56,6 +56,7 @@ >> VLOG_DEFINE_THIS_MODULE(test_ovsdb); >> >> struct test_ovsdb_pvt_context { >> + bool write_changed_only; >> bool track; >> }; >> >> @@ -91,6 +92,7 @@ parse_options(int argc, char *argv[], struct > test_ovsdb_pvt_context *pvt) >> {"timeout", required_argument, NULL, 't'}, >> {"verbose", optional_argument, NULL, 'v'}, >> {"change-track", optional_argument, NULL, 'c'}, >> + {"write-changed-only", optional_argument, NULL, 'w'}, >> {"magic", required_argument, NULL, OPT_MAGIC}, >> {"no-rename-open-files", no_argument, NULL, > OPT_NO_RENAME_OPEN_FILES}, >> {"help", no_argument, NULL, 'h'}, >> @@ -125,6 +127,10 @@ parse_options(int argc, char *argv[], struct > test_ovsdb_pvt_context *pvt) >> pvt->track = true; >> break; >> >> + case 'w': >> + pvt->write_changed_only = true; >> + break; >> + >> case OPT_MAGIC: >> magic = optarg; >> break; >> @@ -2610,6 +2616,7 @@ update_conditions(struct ovsdb_idl *idl, char > *commands) >> static void >> do_idl(struct ovs_cmdl_context *ctx) >> { >> + struct test_ovsdb_pvt_context *pvt = ctx->pvt; >> struct jsonrpc *rpc; >> struct ovsdb_idl *idl; >> unsigned int seqno = 0; >> @@ -2618,9 +2625,6 @@ do_idl(struct ovs_cmdl_context *ctx) >> int step = 0; >> int error; >> int i; >> - bool track; >> - >> - track = ((struct test_ovsdb_pvt_context *)(ctx->pvt))->track; >> >> idl = ovsdb_idl_create(ctx->argv[1], &idltest_idl_class, true, true); >> ovsdb_idl_set_leader_only(idl, false); >> @@ -2637,10 +2641,14 @@ do_idl(struct ovs_cmdl_context *ctx) >> rpc = NULL; >> } >> >> - if (track) { >> + if (pvt->track) { >> ovsdb_idl_track_add_all(idl); >> } >> >> + if (pvt->write_changed_only) { >> + ovsdb_idl_set_write_change_only_all(idl, true); >> + } >> + >> setvbuf(stdout, NULL, _IONBF, 0); >> >> symtab = ovsdb_symbol_table_create(); >> @@ -2683,7 +2691,7 @@ do_idl(struct ovs_cmdl_context *ctx) >> } >> >> /* Print update. */ >> - if (track) { >> + if (pvt->track) { >> print_idl_track(idl, step++, terse); >> ovsdb_idl_track_clear(idl); >> } else { >> -- >> 2.27.0 >> >> _______________________________________________ >> dev mailing list >> d...@openvswitch.org >> https://mail.openvswitch.org/mailman/listinfo/ovs-dev > _______________________________________________ dev mailing list d...@openvswitch.org https://mail.openvswitch.org/mailman/listinfo/ovs-dev