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Improve management of SLRU statistics collection. 

Instead of re-identifying which statistics bucket to use for a given
SLRU on every counter increment, do it once during shmem initialization.
This saves a fair number of cycles, and there's no real cost because
we could not have a bucket assignment that varies over time or across
backends anyway.

Also, get rid of the ill-considered decision to let pgstat.c pry
directly into SLRU's shared state; it's cleaner just to have slru.c
pass the stats bucket number.

In consequence of these changes, there's no longer any need to store
an SLRU's LWLock tranche info in shared memory, so get rid of that,
making this a net reduction in shmem consumption.  (That partly
reverts fe702a7b3.)

This is basically code review for 28cac71bd, so I also cleaned up
some comments, removed a dangling extern declaration, fixed some
things that should be static and/or const, etc.

Discussion: https://postgr.es/m/3618.1589313035@sss.pgh.pa.us
This commit is contained in:
Tom Lane 2020-05-13 13:08:12 -04:00
parent 850196b610
commit 81ca868630
5 changed files with 77 additions and 86 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
src/backend/access/transam/slru.c
View File

@ -191,6 +191,8 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
/* shared->latest_page_number will be set later */
shared->slru_stats_idx = pgstat_slru_index(name);
ptr = (char *) shared;
offset = MAXALIGN(sizeof(SlruSharedData));
shared->page_buffer = (char **) (ptr + offset);
@ -214,15 +216,11 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
offset += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr));
}
Assert(strlen(name) + 1 < SLRU_MAX_NAME_LENGTH);
strlcpy(shared->lwlock_tranche_name, name, SLRU_MAX_NAME_LENGTH);
shared->lwlock_tranche_id = tranche_id;
ptr += BUFFERALIGN(offset);
for (slotno = 0; slotno < nslots; slotno++)
{
LWLockInitialize(&shared->buffer_locks[slotno].lock,
shared->lwlock_tranche_id);
tranche_id);
shared->page_buffer[slotno] = ptr;
shared->page_status[slotno] = SLRU_PAGE_EMPTY;
@ -238,8 +236,7 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
Assert(found);
/* Register SLRU tranche in the main tranches array */
LWLockRegisterTranche(shared->lwlock_tranche_id,
shared->lwlock_tranche_name);
LWLockRegisterTranche(tranche_id, name);
/*
* Initialize the unshared control struct, including directory path. We
@ -287,7 +284,7 @@ SimpleLruZeroPage(SlruCtl ctl, int pageno)
shared->latest_page_number = pageno;
/* update the stats counter of zeroed pages */
pgstat_count_slru_page_zeroed(ctl);
pgstat_count_slru_page_zeroed(shared->slru_stats_idx);
return slotno;
}
@ -408,7 +405,7 @@ SimpleLruReadPage(SlruCtl ctl, int pageno, bool write_ok,
SlruRecentlyUsed(shared, slotno);
/* update the stats counter of pages found in the SLRU */
pgstat_count_slru_page_hit(ctl);
pgstat_count_slru_page_hit(shared->slru_stats_idx);
return slotno;
}
@ -453,7 +450,7 @@ SimpleLruReadPage(SlruCtl ctl, int pageno, bool write_ok,
SlruRecentlyUsed(shared, slotno);
/* update the stats counter of pages not found in SLRU */
pgstat_count_slru_page_read(ctl);
pgstat_count_slru_page_read(shared->slru_stats_idx);
return slotno;
}
@ -493,7 +490,7 @@ SimpleLruReadPage_ReadOnly(SlruCtl ctl, int pageno, TransactionId xid)
SlruRecentlyUsed(shared, slotno);
/* update the stats counter of pages found in the SLRU */
pgstat_count_slru_page_hit(ctl);
pgstat_count_slru_page_hit(shared->slru_stats_idx);
return slotno;
}
@ -612,7 +609,7 @@ SimpleLruDoesPhysicalPageExist(SlruCtl ctl, int pageno)
off_t endpos;
/* update the stats counter of checked pages */
pgstat_count_slru_page_exists(ctl);
pgstat_count_slru_page_exists(ctl->shared->slru_stats_idx);
SlruFileName(ctl, path, segno);
@ -749,7 +746,7 @@ SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruFlush fdata)
int fd = -1;
/* update the stats counter of written pages */
pgstat_count_slru_page_written(ctl);
pgstat_count_slru_page_written(shared->slru_stats_idx);
/*
* Honor the write-WAL-before-data rule, if appropriate, so that we do not
@ -1147,7 +1144,7 @@ SimpleLruFlush(SlruCtl ctl, bool allow_redirtied)
bool ok;
/* update the stats counter of flushes */
pgstat_count_slru_flush(ctl);
pgstat_count_slru_flush(shared->slru_stats_idx);
/*
* Find and write dirty pages
@ -1211,7 +1208,7 @@ SimpleLruTruncate(SlruCtl ctl, int cutoffPage)
int slotno;
/* update the stats counter of truncates */
pgstat_count_slru_truncate(ctl);
pgstat_count_slru_truncate(shared->slru_stats_idx);
/*
* The cutoff point is the start of the segment containing cutoffPage.

98
src/backend/postmaster/pgstat.c
View File

@ -142,24 +142,30 @@ char *pgstat_stat_tmpname = NULL;
PgStat_MsgBgWriter BgWriterStats;
/*
* SLRU statistics counters (unused in other processes) stored directly in
* stats structure so it can be sent without needing to copy things around.
* We assume this inits to zeroes. There is no central registry of SLRUs,
* so we use this fixed list instead.
*
* There's a separte entry for each SLRU we have. The "other" entry is used
* for all SLRUs without an explicit entry (e.g. SLRUs in extensions).
* List of SLRU names that we keep stats for. There is no central registry of
* SLRUs, so we use this fixed list instead. The "other" entry is used for
* all SLRUs without an explicit entry (e.g. SLRUs in extensions).
*/
static char *slru_names[] = {"async", "clog", "commit_timestamp",
"multixact_offset", "multixact_member",
"oldserxid", "subtrans",
"other" /* has to be last */};
static const char *const slru_names[] = {
"async",
"clog",
"commit_timestamp",
"multixact_offset",
"multixact_member",
"oldserxid",
"subtrans",
"other" /* has to be last */
};
/* number of elemenents of slru_name array */
#define SLRU_NUM_ELEMENTS (sizeof(slru_names) / sizeof(char *))
#define SLRU_NUM_ELEMENTS lengthof(slru_names)
/* entries in the same order as slru_names */
PgStat_MsgSLRU SLRUStats[SLRU_NUM_ELEMENTS];
/*
* SLRU statistics counts waiting to be sent to the collector. These are
* stored directly in stats message format so they can be sent without needing
* to copy things around. We assume this variable inits to zeroes. Entries
* are one-to-one with slru_names[].
*/
static PgStat_MsgSLRU SLRUStats[SLRU_NUM_ELEMENTS];
/* ----------
* Local data
@ -4411,12 +4417,10 @@ pgstat_send_bgwriter(void)
static void
pgstat_send_slru(void)
{
int i;
/* We assume this initializes to zeroes */
static const PgStat_MsgSLRU all_zeroes;
for (i = 0; i < SLRU_NUM_ELEMENTS; i++)
for (int i = 0; i < SLRU_NUM_ELEMENTS; i++)
{
/*
* This function can be called even if nothing at all has happened. In
@ -6705,15 +6709,13 @@ pgstat_slru_index(const char *name)
* in which case this returns NULL. This allows writing code that does not
* know the number of entries in advance.
*/
char *
pgstat_slru_name(int idx)
const char *
pgstat_slru_name(int slru_idx)
{
Assert(idx >= 0);
if (idx >= SLRU_NUM_ELEMENTS)
if (slru_idx < 0 || slru_idx >= SLRU_NUM_ELEMENTS)
return NULL;
return slru_names[idx];
return slru_names[slru_idx];
}
/*
@ -6722,54 +6724,56 @@ pgstat_slru_name(int idx)
* Returns pointer to entry with counters for given SLRU (based on the name
* stored in SlruCtl as lwlock tranche name).
*/
static PgStat_MsgSLRU *
slru_entry(SlruCtl ctl)
static inline PgStat_MsgSLRU *
slru_entry(int slru_idx)
{
int idx = pgstat_slru_index(ctl->shared->lwlock_tranche_name);
Assert((slru_idx >= 0) && (slru_idx < SLRU_NUM_ELEMENTS));
Assert((idx >= 0) && (idx < SLRU_NUM_ELEMENTS));
return &SLRUStats[slru_idx];
}
return &SLRUStats[idx];
/*
* SLRU statistics count accumulation functions --- called from slru.c
*/
void
pgstat_count_slru_page_zeroed(int slru_idx)
{
slru_entry(slru_idx)->m_blocks_zeroed += 1;
}
void
pgstat_count_slru_page_zeroed(SlruCtl ctl)
pgstat_count_slru_page_hit(int slru_idx)
{
slru_entry(ctl)->m_blocks_zeroed += 1;
slru_entry(slru_idx)->m_blocks_hit += 1;
}
void
pgstat_count_slru_page_hit(SlruCtl ctl)
pgstat_count_slru_page_exists(int slru_idx)
{
slru_entry(ctl)->m_blocks_hit += 1;
slru_entry(slru_idx)->m_blocks_exists += 1;
}
void
pgstat_count_slru_page_exists(SlruCtl ctl)
pgstat_count_slru_page_read(int slru_idx)
{
slru_entry(ctl)->m_blocks_exists += 1;
slru_entry(slru_idx)->m_blocks_read += 1;
}
void
pgstat_count_slru_page_read(SlruCtl ctl)
pgstat_count_slru_page_written(int slru_idx)
{
slru_entry(ctl)->m_blocks_read += 1;
slru_entry(slru_idx)->m_blocks_written += 1;
}
void
pgstat_count_slru_page_written(SlruCtl ctl)
pgstat_count_slru_flush(int slru_idx)
{
slru_entry(ctl)->m_blocks_written += 1;
slru_entry(slru_idx)->m_flush += 1;
}
void
pgstat_count_slru_flush(SlruCtl ctl)
pgstat_count_slru_truncate(int slru_idx)
{
slru_entry(ctl)->m_flush += 1;
}
void
pgstat_count_slru_truncate(SlruCtl ctl)
{
slru_entry(ctl)->m_truncate += 1;
slru_entry(slru_idx)->m_truncate += 1;
}

2
src/backend/utils/adt/pgstatfuncs.c
View File

@ -1739,7 +1739,7 @@ pg_stat_get_slru(PG_FUNCTION_ARGS)
Datum values[PG_STAT_GET_SLRU_COLS];
bool nulls[PG_STAT_GET_SLRU_COLS];
PgStat_SLRUStats stat = stats[i];
char *name;
const char *name;
name = pgstat_slru_name(i);

10
src/include/access/slru.h
View File

@ -32,9 +32,6 @@
*/
#define SLRU_PAGES_PER_SEGMENT 32
/* Maximum length of an SLRU name */
#define SLRU_MAX_NAME_LENGTH 32
/*
* Page status codes. Note that these do not include the "dirty" bit.
* page_dirty can be true only in the VALID or WRITE_IN_PROGRESS states;
@ -68,6 +65,7 @@ typedef struct SlruSharedData
bool *page_dirty;
int *page_number;
int *page_lru_count;
LWLockPadded *buffer_locks;
/*
* Optional array of WAL flush LSNs associated with entries in the SLRU
@ -98,10 +96,8 @@ typedef struct SlruSharedData
*/
int latest_page_number;
/* LWLocks */
int lwlock_tranche_id;
char lwlock_tranche_name[SLRU_MAX_NAME_LENGTH];
LWLockPadded *buffer_locks;
/* SLRU's index for statistics purposes (might not be unique) */
int slru_stats_idx;
} SlruSharedData;
typedef SlruSharedData *SlruShared;

26
src/include/pgstat.h
View File

@ -11,7 +11,6 @@
#ifndef PGSTAT_H
#define PGSTAT_H
#include "access/slru.h"
#include "datatype/timestamp.h"
#include "libpq/pqcomm.h"
#include "miscadmin.h"
@ -438,7 +437,7 @@ typedef struct PgStat_MsgBgWriter
} PgStat_MsgBgWriter;
/* ----------
* PgStat_MsgSLRU Sent by the SLRU to update statistics.
* PgStat_MsgSLRU Sent by a backend to update SLRU statistics.
* ----------
*/
typedef struct PgStat_MsgSLRU
@ -1260,11 +1259,6 @@ extern char *pgstat_stat_filename;
*/
extern PgStat_MsgBgWriter BgWriterStats;
/*
* SLRU statistics counters are updated directly by slru.
*/
extern PgStat_MsgSLRU SlruStats[];
/*
* Updated by pgstat_count_buffer_*_time macros
*/
@ -1480,14 +1474,14 @@ extern PgStat_ArchiverStats *pgstat_fetch_stat_archiver(void);
extern PgStat_GlobalStats *pgstat_fetch_global(void);
extern PgStat_SLRUStats *pgstat_fetch_slru(void);
extern void pgstat_count_slru_page_zeroed(SlruCtl ctl);
extern void pgstat_count_slru_page_hit(SlruCtl ctl);
extern void pgstat_count_slru_page_read(SlruCtl ctl);
extern void pgstat_count_slru_page_written(SlruCtl ctl);
extern void pgstat_count_slru_page_exists(SlruCtl ctl);
extern void pgstat_count_slru_flush(SlruCtl ctl);
extern void pgstat_count_slru_truncate(SlruCtl ctl);
extern char *pgstat_slru_name(int idx);
extern int pgstat_slru_index(const char *name);
extern void pgstat_count_slru_page_zeroed(int slru_idx);
extern void pgstat_count_slru_page_hit(int slru_idx);
extern void pgstat_count_slru_page_read(int slru_idx);
extern void pgstat_count_slru_page_written(int slru_idx);
extern void pgstat_count_slru_page_exists(int slru_idx);
extern void pgstat_count_slru_flush(int slru_idx);
extern void pgstat_count_slru_truncate(int slru_idx);
extern const char *pgstat_slru_name(int slru_idx);
extern int pgstat_slru_index(const char *name);
#endif /* PGSTAT_H */