From 3c6314b72d9323dd1554deadedf1c57fe105ad6b Mon Sep 17 00:00:00 2001 From: Justin Pryzby Date: Sun, 19 Jan 2020 22:35:01 -0600 Subject: [PATCH v3 2/2] docs/comments review for parallel vacuum --- doc/src/sgml/ref/vacuum.sgml | 12 ++++++------ src/backend/access/heap/vacuumlazy.c | 22 +++++++++++----------- src/backend/commands/vacuum.c | 2 +- 3 files changed, 18 insertions(+), 18 deletions(-) diff --git a/doc/src/sgml/ref/vacuum.sgml b/doc/src/sgml/ref/vacuum.sgml index b7e0a8af6b..5dc0787459 100644 --- a/doc/src/sgml/ref/vacuum.sgml +++ b/doc/src/sgml/ref/vacuum.sgml @@ -232,9 +232,9 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ integer - background workers (for the detail of each vacuum phase, please + background workers (for the details of each vacuum phase, please refer to ). If the PARALLEL option is omitted, then the number of workers is determined based on the number of indexes that support parallel vacuum @@ -358,16 +358,16 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ for details. diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c index a757560996..dfa57df7b6 100644 --- a/src/backend/access/heap/vacuumlazy.c +++ b/src/backend/access/heap/vacuumlazy.c @@ -232,8 +232,8 @@ typedef struct LVShared /* * Number of active parallel workers. This is used for computing the - * minimum threshold of the vacuum cost balance for a worker to go for the - * delay. + * minimum threshold of the vacuum cost balance before a worker sleeps + * for cost-based delay. */ pg_atomic_uint32 active_nworkers; @@ -2312,12 +2312,12 @@ vacuum_one_index(Relation indrel, IndexBulkDeleteResult **stats, /* * Copy the index bulk-deletion result returned from ambulkdelete and - * amvacuumcleanup to the DSM segment if it's the first time to get it - * from them, because they allocate it locally and it's possible that an - * index will be vacuumed by the different vacuum process at the next - * time. The copying of the result normally happens only after the first - * time of index vacuuming. From the second time, we pass the result on - * the DSM segment so that they then update it directly. + * amvacuumcleanup to the DSM segment if it's the first time to get a result + * from a worker, because workers allocate BulkDeleteResults locally, and it's possible that an + * index will be vacuumed by a different vacuum process the next + * time. Copying the result normally happens only the first + * time an index is vacuumed. For any additional vacuums, we pass the result on + * the DSM segment so that workers then update it directly. * * Since all vacuum workers write the bulk-deletion result at different * slots we can write them without locking. @@ -3138,7 +3138,7 @@ prepare_index_statistics(LVShared *lvshared, bool *can_parallel_vacuum, if (!can_parallel_vacuum[i]) continue; - /* Set NOT NULL as this index do support parallelism */ + /* Set NOT NULL as this index does support parallelism */ lvshared->bitmap[i >> 3] |= 1 << (i & 0x07); } } @@ -3174,7 +3174,7 @@ update_index_statistics(Relation *Irel, IndexBulkDeleteResult **stats, /* * This function prepares and returns parallel vacuum state if we can launch - * even one worker. This function is responsible to enter parallel mode, + * even one worker. This function is responsible for entering parallel mode, * create a parallel context, and then initialize the DSM segment. */ static LVParallelState * @@ -3346,7 +3346,7 @@ begin_parallel_vacuum(Oid relid, Relation *Irel, LVRelStats *vacrelstats, * Destroy the parallel context, and end parallel mode. * * Since writes are not allowed during parallel mode, copy the - * updated index statistics from DSM in local memory and then later use that + * updated index statistics from DSM into local memory and then later use that * to update the index statistics. One might think that we can exit from * parallel mode, update the index statistics and then destroy parallel * context, but that won't be safe (see ExitParallelMode). diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c index 495ac23a26..351d5215a9 100644 --- a/src/backend/commands/vacuum.c +++ b/src/backend/commands/vacuum.c @@ -2040,7 +2040,7 @@ vacuum_delay_point(void) * worker to sleep in proportion to the share of work it's done. We achieve this * by allowing all parallel vacuum workers including the leader process to * have a shared view of cost related parameters (mainly VacuumCostBalance). - * We allow each worker to update it as and when it has incurred any cost and + * We allow each worker to update it AS AND WHEN it has incurred any cost and * then based on that decide whether it needs to sleep. We compute the time * to sleep for a worker based on the cost it has incurred * (VacuumCostBalanceLocal) and then reduce the VacuumSharedCostBalance by -- 2.17.0