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PG-488: pg_stat_monitor: Overflow management.

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Reimplement the storage mechanism of buckets and query texts
using Dynamic shared memory. Since the dynamic shared memory
can grow into a swap area, so we get the overflow out of the box.

oreover the new design saves the query pointer inside the bucket
and eventually, the query text gets evicted with the bucket recycle.

Finally, the dynamic shared memory hash has a built-in locking
mechanism so we can revisit the whole locking in pg_stat_monitor
has potential for lots of performance improvements
This commit is contained in:
Muhammad Usama
2022-12-20 17:29:15 +05:00
parent 5a6b824737
commit df0580b741
3 changed files with 246 additions and 513 deletions
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44
pg_stat_monitor.h
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@@ -27,6 +27,9 @@
#include <sys/time.h>
#include <sys/resource.h>
#include "lib/dshash.h"
#include "utils/dsa.h"
#include "access/hash.h"
#include "catalog/pg_authid.h"
#include "executor/instrument.h"
@@ -179,20 +182,6 @@ typedef struct CallTime
double sum_var_time; /* sum of variances in execution time in msec */
} CallTime;
/*
* Entry type for queries hash table (query ID).
*
* We use a hash table to keep track of query IDs that have their
* corresponding query text added to the query buffer (pgsm_query_shared_buffer).
*
* This allow us to avoid adding duplicated queries to the buffer, therefore
* leaving more space for other queries and saving some CPU.
*/
typedef struct pgssQueryEntry
{
uint64 queryid; /* query identifier, also the key. */
size_t query_pos; /* query location within query buffer */
} pgssQueryEntry;
typedef struct PlanInfo
{
@@ -216,6 +205,7 @@ typedef struct pgssHashKey
typedef struct QueryInfo
{
uint64 parentid; /* parent queryid of current query */
dsa_pointer parent_query;
int64 type; /* type of query, options are query, info,
* warning, error, fatal */
char application_name[APPLICATIONNAME_LEN];
@@ -322,7 +312,7 @@ typedef struct pgssEntry
Counters counters; /* the statistics for this query */
int encoding; /* query text encoding */
slock_t mutex; /* protects the counters only */
size_t query_pos; /* query location within query buffer */
dsa_pointer query_pos; /* query location within query buffer */
} pgssEntry;
/*
@@ -353,10 +343,19 @@ typedef struct pgssSharedState
* This allows us to avoid having a large file on disk that would also
* slowdown queries to the pg_stat_monitor view.
*/
bool overflow;
size_t n_bucket_cycles;
int hash_tranche_id;
void *raw_dsa_area;
dshash_table_handle hash_handle;
} pgssSharedState;
typedef struct pgsmLocalState
{
pgssSharedState *shared_pgssState;
dsa_area *dsa;
dshash_table *shared_hash;
}pgsmLocalState;
#define ResetSharedState(x) \
do { \
x->cur_median_usage = ASSUMED_MEDIAN_INIT; \
@@ -418,27 +417,22 @@ void init_guc(void);
GucVariable *get_conf(int i);
/* hash_create.c */
dsa_area *get_dsa_area_for_query_text(void);
dshash_table *get_pgssHash(void);
void pgsm_attach_shmem(void);
bool IsHashInitialize(void);
void pgss_shmem_startup(void);
void pgss_shmem_shutdown(int code, Datum arg);
int pgsm_get_bucket_size(void);
pgssSharedState *pgsm_get_ss(void);
HTAB *pgsm_get_plan_hash(void);
HTAB *pgsm_get_hash(void);
HTAB *pgsm_get_query_hash(void);
HTAB *pgsm_get_plan_hash(void);
void hash_entry_reset(void);
void hash_query_entryies_reset(void);
void hash_query_entries();
void hash_query_entry_dealloc(int new_bucket_id, int old_bucket_id, unsigned char *query_buffer[]);
void hash_entry_dealloc(int new_bucket_id, int old_bucket_id, unsigned char *query_buffer);
pgssEntry *hash_entry_alloc(pgssSharedState *pgss, pgssHashKey *key, int encoding);
Size hash_memsize(void);
int read_query_buffer(int bucket_id, uint64 queryid, char *query_txt, size_t pos);
uint64 read_query(unsigned char *buf, uint64 queryid, char *query, size_t pos);
Size pgsm_ShmemSize(void);
void pgss_startup(void);
void set_qbuf(unsigned char *);
/* hash_query.c */
void pgss_startup(void);