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Comments and doc fixes for commit 40d964ec99.

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Reported-by: Justin Pryzby
Author: Justin Pryzby, with few changes by me
Reviewed-by: Amit Kapila and Sawada Masahiko
Discussion: https://postgr.es/m/20200322021801.GB2563@telsasoft.com
This commit is contained in:
Amit Kapila
2020-04-14 08:10:27 +05:30
parent 826ee1a019
commit a6fea120a7
5 changed files with 49 additions and 49 deletions
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52
src/backend/access/heap/vacuumlazy.c
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@ -208,7 +208,7 @@ 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;
@ -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;
@ -732,7 +732,7 @@ vacuum_log_cleanup_info(Relation rel, LVRelStats *vacrelstats)
* 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
@ -809,8 +809,8 @@ 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
* can be used for an index, so we invoke parallelism only if there are at
* 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.
*/
if (params->nworkers >= 0 && vacrelstats->useindex && nindexes > 1)
@ -837,7 +837,7 @@ 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))
@ -2215,7 +2215,7 @@ 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 ||
@ -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 cycle because they
* allocate locally and it's possible that an index will be vacuumed by a
* different vacuum process the next cycle. Copying the result normally
* happens only the first time an index is vacuumed. For any additional
* vacuum pass, we directly point to the result on the DSM segment and
* pass it to vacuum index APIs so that workers can update it directly.
*
* Since all vacuum workers write the bulk-deletion result at different
* slots we can write them without locking.
@ -2328,8 +2328,8 @@ 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
* the locally allocated results.
* Now that stats[idx] points to the DSM segment, we don't need the
* locally allocated results.
*/
pfree(*stats);
*stats = bulkdelete_res;
@ -2449,7 +2449,7 @@ 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,
@ -3050,9 +3050,9 @@ 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
@ -3071,7 +3071,7 @@ 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)
@ -3138,13 +3138,13 @@ 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);
}
}
/*
* 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,
@ -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 *
@ -3345,8 +3345,8 @@ 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
* updated index statistics from DSM in local memory and then later use that
* Since writes are not allowed during parallel mode, copy the
* 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).
@ -3452,7 +3452,7 @@ 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)

2
src/backend/access/transam/parallel.c
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@ -505,7 +505,7 @@ 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.
*/

20
src/backend/commands/vacuum.c
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@ -2036,23 +2036,23 @@ 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 allow 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
* 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
* 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%
* We allow 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. 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

2
src/include/commands/vacuum.h
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@ -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;