doc review for parallel vacuum

Original, long thread
https://www.postgresql.org/message-id/flat/CAA4eK1%2Bnw1FBK3_sDnW%2B7kB%2Bx4qbDJqetgqwYW8k2xv82RZ%2BKw%40mail.gmail.com#b1745ee853b137043e584b500b41300f

diff --git a/doc/src/sgml/ref/vacuum.sgml b/doc/src/sgml/ref/vacuum.sgml
index ab1b8c2398..140637983a 100644
--- a/doc/src/sgml/ref/vacuum.sgml
+++ b/doc/src/sgml/ref/vacuum.sgml
@@ -237,15 +237,15 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
<term><literal>PARALLEL</literal></term>
<listitem>
<para>
- Perform vacuum index and cleanup index phases of <command>VACUUM</command>
+ Perform vacuum index and index cleanup phases of <command>VACUUM</command>
in parallel using <replaceable class="parameter">integer</replaceable>
- background workers (for the detail of each vacuum phases, please
+ background workers (for the detail of each vacuum phase, please
refer to <xref linkend="vacuum-phases"/>). If the
- <literal>PARALLEL</literal> option is omitted, then
- <command>VACUUM</command> decides the number of workers based on number
- of indexes that support parallel vacuum operation on the relation which
- is further limited by <xref linkend="guc-max-parallel-workers-maintenance"/>.
- The index can participate in a parallel vacuum if and only if the size
+ <literal>PARALLEL</literal> option is omitted, then the number of workers
+ is determined based on the number of indexes that support parallel vacuum
+ operation on the relation, and is further limited by <xref
+ linkend="guc-max-parallel-workers-maintenance"/>.
+ An index can participate in parallel vacuum if and only if the size
of the index is more than <xref linkend="guc-min-parallel-index-scan-size"/>.
Please note that it is not guaranteed that the number of parallel workers
specified in <replaceable class="parameter">integer</replaceable> will
@@ -253,7 +253,7 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
workers than specified, or even with no workers at all. Only one worker
can be used per index. So parallel workers are launched only when there
are at least <literal>2</literal> indexes in the table. Workers for
- vacuum launches before starting each phase and exit at the end of
+ vacuum are launched before the start of each phase and terminate at the end of
the phase. These behaviors might change in a future release. This
option can't be used with the <literal>FULL</literal> option.
</para>
@@ -372,7 +372,7 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
<command>VACUUM</command> causes a substantial increase in I/O traffic,
which might cause poor performance for other active sessions. Therefore,
it is sometimes advisable to use the cost-based vacuum delay feature. For
- parallel vacuum, each worker sleeps proportional to the work done by that
+ parallel vacuum, each worker sleeps proportionally to the work done by that
worker. See <xref linkend="runtime-config-resource-vacuum-cost"/> for
details.
</para>

diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index e017db4446..0ab0bea312 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -194,7 +194,7 @@ typedef struct LVShared
* live tuples in the index vacuum case or the new live tuples in the
* index cleanup case.
*
- * estimated_count is true if the reltuples is an estimated value.
+ * estimated_count is true if reltuples is an estimated value.
*/
double reltuples;
bool estimated_count;
@@ -757,7 +757,7 @@ skip_blocks(Relation onerel, VacuumParams *params, BlockNumber *next_unskippable
* to reclaim dead line pointers.
*
* If the table has at least two indexes, we execute both index vacuum
- * and index cleanup with parallel workers unless the parallel vacuum is
+ * and index cleanup with parallel workers unless parallel vacuum is
* disabled. In a parallel vacuum, we enter parallel mode and then
* create both the parallel context and the DSM segment before starting
* heap scan so that we can record dead tuples to the DSM segment. All
@@ -836,7 +836,7 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
vacrelstats->latestRemovedXid = InvalidTransactionId;

/*
- * Initialize the state for a parallel vacuum. As of now, only one worker
+ * Initialize state for a parallel vacuum. As of now, only one worker
* can be used for an index, so we invoke parallelism only if there are at
* least two indexes on a table.
*/
@@ -864,7 +864,7 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
}

/*
- * Allocate the space for dead tuples in case the parallel vacuum is not
+ * Allocate the space for dead tuples in case parallel vacuum is not
* initialized.
*/
if (!ParallelVacuumIsActive(lps))
@@ -2111,7 +2111,7 @@ parallel_vacuum_index(Relation *Irel, IndexBulkDeleteResult **stats,
shared_indstats = get_indstats(lvshared, idx);

/*
- * Skip processing indexes that doesn't participate in parallel
+ * Skip processing indexes that don't participate in parallel
* operation
*/
if (shared_indstats == NULL ||
@@ -2223,7 +2223,7 @@ vacuum_one_index(Relation indrel, IndexBulkDeleteResult **stats,
shared_indstats->updated = true;

/*
- * Now that the stats[idx] points to the DSM segment, we don't need
+ * Now that stats[idx] points to the DSM segment, we don't need
* the locally allocated results.
*/
pfree(*stats);
@@ -2329,7 +2329,7 @@ lazy_vacuum_index(Relation indrel, IndexBulkDeleteResult **stats,
* lazy_cleanup_index() -- do post-vacuum cleanup for one index relation.
*
* reltuples is the number of heap tuples and estimated_count is true
- * if the reltuples is an estimated value.
+ * if reltuples is an estimated value.
*/
static void
lazy_cleanup_index(Relation indrel,
@@ -2916,9 +2916,9 @@ heap_page_is_all_visible(Relation rel, Buffer buf,
/*
* Compute the number of parallel worker processes to request. Both index
* vacuum and index cleanup can be executed with parallel workers. The index
- * is eligible for parallel vacuum iff it's size is greater than
+ * is eligible for parallel vacuum iff its size is greater than
* min_parallel_index_scan_size as invoking workers for very small indexes
- * can hurt the performance.
+ * can hurt performance.
*
* nrequested is the number of parallel workers that user requested. If
* nrequested is 0, we compute the parallel degree based on nindexes, that is
@@ -2937,7 +2937,7 @@ compute_parallel_vacuum_workers(Relation *Irel, int nindexes, int nrequested,
int i;

/*
- * We don't allow to perform parallel operation in standalone backend or
+ * We don't allow performing parallel operation in standalone backend or
* when parallelism is disabled.
*/
if (!IsUnderPostmaster || max_parallel_maintenance_workers == 0)
@@ -3010,7 +3010,7 @@ prepare_index_statistics(LVShared *lvshared, bool *can_parallel_vacuum,
}

/*
- * Update index statistics in pg_class if the statistics is accurate.
+ * Update index statistics in pg_class if the statistics are accurate.
*/
static void
update_index_statistics(Relation *Irel, IndexBulkDeleteResult **stats,
@@ -3181,7 +3181,7 @@ begin_parallel_vacuum(Oid relid, Relation *Irel, LVRelStats *vacrelstats,
/*
* Destroy the parallel context, and end parallel mode.
*
- * Since writes are not allowed during the parallel mode, so we copy the
+ * Since writes are not allowed during parallel mode, copy the
* updated index statistics from DSM in 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
@@ -3288,7 +3288,7 @@ skip_parallel_vacuum_index(Relation indrel, LVShared *lvshared)
* Perform work within a launched parallel process.
*
* Since parallel vacuum workers perform only index vacuum or index cleanup,
- * we don't need to report the progress information.
+ * we don't need to report progress information.
*/
void
parallel_vacuum_main(dsm_segment *seg, shm_toc *toc)
diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c
index df06e7d174..ac348b312c 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -493,7 +493,7 @@ ReinitializeParallelDSM(ParallelContext *pcxt)

/*
* Reinitialize parallel workers for a parallel context such that we could
- * launch the different number of workers. This is required for cases where
+ * launch a different number of workers. This is required for cases where
* we need to reuse the same DSM segment, but the number of workers can
* vary from run-to-run.
*/
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index d625d17bf4..76d33b1ba2 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -2034,23 +2034,23 @@ vacuum_delay_point(void)
/*
* Computes the vacuum delay for parallel workers.
*
- * The basic idea of a cost-based vacuum delay for parallel vacuum is to allow
- * each worker to sleep proportional to the work done by it. We achieve this
+ * The basic idea of a cost-based delay for parallel vacuum is to force
+ * each 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
- * that amount. This avoids letting the workers sleep who have done less or
- * no I/O as compared to other workers and therefore can ensure that workers
- * who are doing more I/O got throttled more.
+ * that amount. This avoids putting to sleep those workers which have done less
+ * I/O than other workers and therefore ensure that workers
+ * which are doing more I/O got throttled more.
*
- * We allow any worker to sleep only if it has performed the I/O above a
+ * We force a worker to sleep only if it has performed I/O above a
* certain threshold, which is calculated based on the number of active
* workers (VacuumActiveNWorkers), and the overall cost balance is more than
- * VacuumCostLimit set by the system. The testing reveals that we achieve
- * the required throttling if we allow a worker that has done more than 50%
+ * VacuumCostLimit set by the system. Testing reveals that we achieve
+ * the required throttling if we force a worker that has done more than 50%
* of its share of work to sleep.
*/
static double
diff --git a/src/include/commands/vacuum.h b/src/include/commands/vacuum.h
index 2779bea5c9..a4cd721400 100644
--- a/src/include/commands/vacuum.h
+++ b/src/include/commands/vacuum.h
@@ -225,7 +225,7 @@ typedef struct VacuumParams

/*
* The number of parallel vacuum workers. 0 by default which means choose
- * based on the number of indexes. -1 indicates a parallel vacuum is
+ * based on the number of indexes. -1 indicates parallel vacuum is
* disabled.
*/
int nworkers;
--
2.17.0