From d6783896069de828b13c554c4c21ce439a76d2bc Mon Sep 17 00:00:00 2001 From: Jakub Wartak Date: Wed, 18 Mar 2026 07:24:14 +0100 Subject: [PATCH v10f 2/3] Lower pg_stat_io_histogram private (backend) memory in pending_hist_time_buckets by using array with indirect offsets. --- src/backend/utils/activity/pgstat.c | 9 +-- src/backend/utils/activity/pgstat_io.c | 90 ++++++++++++++++++++++++-- src/include/pgstat.h | 19 ++++-- src/include/utils/pgstat_internal.h | 1 + 4 files changed, 102 insertions(+), 17 deletions(-) diff --git a/src/backend/utils/activity/pgstat.c b/src/backend/utils/activity/pgstat.c index 9feb2f1370b..7c597932671 100644 --- a/src/backend/utils/activity/pgstat.c +++ b/src/backend/utils/activity/pgstat.c @@ -445,6 +445,7 @@ static const PgStat_KindInfo pgstat_kind_builtin_infos[PGSTAT_KIND_BUILTIN_SIZE] .shared_data_off = offsetof(PgStatShared_IO, stats), .shared_data_len = sizeof(((PgStatShared_IO *) 0)->stats), + .init_backend_cb = pgstat_io_init_backend_cb, .flush_static_cb = pgstat_io_flush_cb, .init_shmem_cb = pgstat_io_init_shmem_cb, .reset_all_cb = pgstat_io_reset_all_cb, @@ -691,14 +692,6 @@ pgstat_initialize(void) /* Set up a process-exit hook to clean up */ before_shmem_exit(pgstat_shutdown_hook, 0); - /* Allocate I/O latency buckets only if we are going to populate it */ - if (track_io_timing || track_wal_io_timing) - PendingIOStats.pending_hist_time_buckets = MemoryContextAllocZero(TopMemoryContext, - IOOBJECT_NUM_TYPES * IOCONTEXT_NUM_TYPES * IOOP_NUM_TYPES * - PGSTAT_IO_HIST_BUCKETS * sizeof(uint64)); - else - PendingIOStats.pending_hist_time_buckets = NULL; - #ifdef USE_ASSERT_CHECKING pgstat_is_initialized = true; #endif diff --git a/src/backend/utils/activity/pgstat_io.c b/src/backend/utils/activity/pgstat_io.c index bbf910ac4bb..1696f278a77 100644 --- a/src/backend/utils/activity/pgstat_io.c +++ b/src/backend/utils/activity/pgstat_io.c @@ -16,6 +16,7 @@ #include "postgres.h" +#include "access/xlog.h" #include "executor/instrument.h" #include "port/pg_bitutils.h" #include "storage/bufmgr.h" @@ -66,6 +67,27 @@ pgstat_bktype_io_stats_valid(PgStat_BktypeIO *backend_io, return true; } +int +pgstat_bktype_count_potentially_used(BackendType bktype) +{ + int cnt = 0; + + for (int io_object = 0; io_object < IOOBJECT_NUM_TYPES; io_object++) + { + for (int io_context = 0; io_context < IOCONTEXT_NUM_TYPES; io_context++) + { + for (int io_op = 0; io_op < IOOP_NUM_TYPES; io_op++) + { + /* we do track it */ + if (pgstat_tracks_io_op(bktype, io_object, io_context, io_op)) + cnt++; + } + } + } + + return cnt; +} + void pgstat_count_io_op(IOObject io_object, IOContext io_context, IOOp io_op, uint32 cnt, uint64 bytes) @@ -186,12 +208,16 @@ pgstat_count_io_op_time(IOObject io_object, IOContext io_context, IOOp io_op, if (PendingIOStats.pending_hist_time_buckets != NULL) { + int offset; + /* * calculate the bucket_index based on latency in nanoseconds * (uint64) */ bucket_index = get_bucket_index(INSTR_TIME_GET_NANOSEC(io_time)); - PendingIOStats.pending_hist_time_buckets[io_object][io_context][io_op][bucket_index]++; + + offset = PendingIOStats.pending_hist_time_buckets_offsets[io_object][io_context][io_op]; + PendingIOStats.pending_hist_time_buckets[offset][bucket_index]++; } /* Add the per-backend count */ @@ -264,10 +290,23 @@ pgstat_io_flush_cb(bool nowait) bktype_shstats->times[io_object][io_context][io_op] += INSTR_TIME_GET_MICROSEC(time); + /* + * If tracking I/O stats, save I/O histograms from backend + * local's PendingIOStats by using indirect offsets from the + * pending_hist_time_buckets dynamic array (accessed with + * offsets to save memory) into shared memory. + */ if (PendingIOStats.pending_hist_time_buckets != NULL) for (int b = 0; b < PGSTAT_IO_HIST_BUCKETS; b++) - bktype_shstats->hist_time_buckets[io_object][io_context][io_op][b] += - PendingIOStats.pending_hist_time_buckets[io_object][io_context][io_op][b]; + { + int pending_off = PendingIOStats.pending_hist_time_buckets_offsets[io_object][io_context][io_op]; + + if (pending_off != -1) + { + bktype_shstats->hist_time_buckets[io_object][io_context][io_op][b] += + PendingIOStats.pending_hist_time_buckets[pending_off][b]; + } + } } } } @@ -276,8 +315,14 @@ pgstat_io_flush_cb(bool nowait) LWLockRelease(bktype_lock); - /* Avoid overwriting latency buckets array pointer */ + /* + * Avoid overwriting histogram latency array (with offsets) and pointer to + * dynamically allocated memory + */ memset(&PendingIOStats, 0, offsetof(PgStat_PendingIO, pending_hist_time_buckets)); + if (PendingIOStats.pending_hist_time_buckets != NULL) + memset(PendingIOStats.pending_hist_time_buckets, 0, + PendingIOStats.pending_hist_time_buckets_size * sizeof(*PendingIOStats.pending_hist_time_buckets)); have_iostats = false; @@ -349,6 +394,43 @@ pgstat_get_io_op_name(IOOp io_op) pg_unreachable(); } +void +pgstat_io_init_backend_cb(void) +{ + /* Allocate I/O latency buckets only if we are going to populate it */ + if (track_io_timing || track_wal_io_timing) + { + int alloc_sz, + io_histograms_used = 0; + + PendingIOStats.pending_hist_time_buckets_size = pgstat_bktype_count_potentially_used(MyBackendType); + alloc_sz = PendingIOStats.pending_hist_time_buckets_size * sizeof(*PendingIOStats.pending_hist_time_buckets); + PendingIOStats.pending_hist_time_buckets = MemoryContextAllocZero(TopMemoryContext, alloc_sz); + + for (int io_object = 0; io_object < IOOBJECT_NUM_TYPES; io_object++) + { + for (int io_context = 0; io_context < IOCONTEXT_NUM_TYPES; io_context++) + { + for (int io_op = 0; io_op < IOOP_NUM_TYPES; io_op++) + { + if (pgstat_tracks_io_op(MyBackendType, io_object, io_context, io_op)) + { + Assert(io_histograms_used <= PendingIOStats.pending_hist_time_buckets_size); + + PendingIOStats.pending_hist_time_buckets_offsets[io_object][io_context][io_op] = + io_histograms_used++; + } + else + PendingIOStats.pending_hist_time_buckets_offsets[io_object][io_context][io_op] = -1; + } + } + } + } + else + PendingIOStats.pending_hist_time_buckets = NULL; + +} + void pgstat_io_init_shmem_cb(void *stats) { diff --git a/src/include/pgstat.h b/src/include/pgstat.h index 34fd93f86dc..984914e69b8 100644 --- a/src/include/pgstat.h +++ b/src/include/pgstat.h @@ -352,12 +352,20 @@ typedef struct PgStat_PendingIO instr_time pending_times[IOOBJECT_NUM_TYPES][IOCONTEXT_NUM_TYPES][IOOP_NUM_TYPES]; /* - * Dynamically allocated array of - * [IOOBJECT_NUM_TYPES][IOCONTEXT_NUM_TYPES] - * [IOOP_NUM_TYPES][PGSTAT_IO_HIST_BUCKETS] only with track_io_timings - * true. + * Dynamically allocated array for pg_stat_io_histograms only when + * track_io_timings is true. pending_hist_time_buckets_offsets is just an + * offset within pending_hist_time_buckets to avoid using unnecessary + * memory. */ - uint64 (*pending_hist_time_buckets)[IOCONTEXT_NUM_TYPES][IOOP_NUM_TYPES][PGSTAT_IO_HIST_BUCKETS]; + uint64 (*pending_hist_time_buckets)[PGSTAT_IO_HIST_BUCKETS]; + uint64 pending_hist_time_buckets_offsets[IOOBJECT_NUM_TYPES][IOCONTEXT_NUM_TYPES][IOOP_NUM_TYPES]; + + /* + * Cache how much histograms we have allocated to avoid repetably calling + * pgstat_bktype_count_potentially_used(MyBackendType) from + * pgstat_io_flush_cb() + */ + int pending_hist_time_buckets_size; } PgStat_PendingIO; extern PgStat_PendingIO PendingIOStats; @@ -645,6 +653,7 @@ extern PgStat_CheckpointerStats *pgstat_fetch_stat_checkpointer(void); extern bool pgstat_bktype_io_stats_valid(PgStat_BktypeIO *backend_io, BackendType bktype); +extern int pgstat_bktype_count_potentially_used(BackendType bktype); extern void pgstat_count_io_op(IOObject io_object, IOContext io_context, IOOp io_op, uint32 cnt, uint64 bytes); extern instr_time pgstat_prepare_io_time(bool track_io_guc); diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h index a3ce8b04723..fcaf21db574 100644 --- a/src/include/utils/pgstat_internal.h +++ b/src/include/utils/pgstat_internal.h @@ -759,6 +759,7 @@ extern void pgstat_function_reset_timestamp_cb(PgStatShared_Common *header, Time extern void pgstat_flush_io(bool nowait); extern bool pgstat_io_flush_cb(bool nowait); +extern void pgstat_io_init_backend_cb(void); extern void pgstat_io_init_shmem_cb(void *stats); extern void pgstat_io_reset_all_cb(TimestampTz ts); extern void pgstat_io_snapshot_cb(void); -- 2.43.0