pg_stat_monitor/hash_query.c

/*-------------------------------------------------------------------------
 *
 * hash_query.c
 *		Track statement execution times across a whole database cluster.
 *
 * Portions Copyright © 2018-2020, Percona LLC and/or its affiliates
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 *
 * Portions Copyright (c) 1994, The Regents of the University of California
 *
 * IDENTIFICATION
 *	  contrib/pg_stat_monitor/hash_query.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
#include "nodes/pg_list.h"
#include "pg_stat_monitor.h"

static pgsmLocalState	pgsmStateLocal;

/* parameter for the shared hash */
 static dshash_parameters dsh_params = {
     sizeof(pgssHashKey),
     sizeof(pgssEntry),
     dshash_memcmp,
     dshash_memhash
 };
static void pgsm_proc_exit(int code, Datum arg);

static Size
pgsm_query_area_size(void)
{
	Size	sz = MAXALIGN(MAX_QUERY_BUF);
	return 	MAXALIGN(sz);
}

Size
pgsm_ShmemSize(void)
 {
    Size	sz = MAXALIGN(sizeof(pgssSharedState));
    sz = add_size(sz, pgsm_query_area_size());
	sz = add_size(sz, hash_estimate_size(MAX_BUCKET_ENTRIES, sizeof(pgssEntry)));
    return sz;
 }

void
pgss_startup(void)
{
	bool		found = false;
	pgssSharedState *pgss;
	/* reset in case this is a restart within the postmaster */
	pgsmStateLocal.dsa = NULL;
	pgsmStateLocal.shared_hash = NULL;
	pgsmStateLocal.shared_pgssState = NULL;

	/*
	 * Create or attach to the shared memory state, including hash table
	 */
	LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);

	pgss = ShmemInitStruct("pg_stat_monitor", pgsm_ShmemSize(), &found);
	if (!found)
	{
		/* First time through ... */
		dsa_area   *dsa;
		dshash_table *dsh;
		char	*p = (char *) pgss;

		pgss->lock = &(GetNamedLWLockTranche("pg_stat_monitor"))->lock;
		SpinLockInit(&pgss->mutex);
		ResetSharedState(pgss);
		/* the allocation of pgssSharedState itself */
		p += MAXALIGN(sizeof(pgssSharedState));
		pgss->raw_dsa_area = p;
		dsa = dsa_create_in_place(pgss->raw_dsa_area,
                                   pgsm_query_area_size(),
                                   LWLockNewTrancheId(), 0);
		dsa_pin(dsa);
		dsa_set_size_limit(dsa, pgsm_query_area_size());

		pgss->hash_tranche_id = LWLockNewTrancheId();

		dsh_params.tranche_id = pgss->hash_tranche_id;
		dsh = dshash_create(dsa, &dsh_params, 0);

		pgss->hash_handle = dshash_get_hash_table_handle(dsh);

		if (PGSM_OVERFLOW_TARGET == OVERFLOW_TARGET_DISK)
			dsa_set_size_limit(dsa, -1);

		pgsmStateLocal.shared_pgssState = pgss;
		/*
		* Postmaster will never access these again, thus free the local
		* dsa/dshash references.
		*/
         dshash_detach(dsh);
         dsa_detach(dsa);
	}

#ifdef BENCHMARK
	init_hook_stats();
#endif

	LWLockRelease(AddinShmemInitLock);

	/*
	 * If we're in the postmaster (or a standalone backend...), set up a shmem
	 * exit hook to dump the statistics to disk.
	 */
	on_shmem_exit(pgss_shmem_shutdown, (Datum) 0);
}

void
pgsm_attach_shmem(void)
{
	MemoryContext oldcontext;
	if (pgsmStateLocal.dsa)
		return;

	oldcontext = MemoryContextSwitchTo(TopMemoryContext);

	pgsmStateLocal.dsa = dsa_attach_in_place(pgsmStateLocal.shared_pgssState->raw_dsa_area,
                                           NULL);
	dsa_pin_mapping(pgsmStateLocal.dsa);

	dsh_params.tranche_id = pgsmStateLocal.shared_pgssState->hash_tranche_id;
	pgsmStateLocal.shared_hash = dshash_attach(pgsmStateLocal.dsa, &dsh_params,
                                             pgsmStateLocal.shared_pgssState->hash_handle, 0);

	on_proc_exit(pgsm_proc_exit, 0);

	MemoryContextSwitchTo(oldcontext);
}

dsa_area*
get_dsa_area_for_query_text(void)
{
	pgsm_attach_shmem();
	return pgsmStateLocal.dsa;
}

dshash_table*
get_pgssHash(void)
{
	pgsm_attach_shmem();
	return pgsmStateLocal.shared_hash;
}

pgssSharedState *
pgsm_get_ss(void)
{
	pgsm_attach_shmem();
	return pgsmStateLocal.shared_pgssState;
}


/*
 * shmem_shutdown hook: Dump statistics into file.
 *
 * Note: we don't bother with acquiring lock, because there should be no
 * other processes running when this is called.
 */
void
pgss_shmem_shutdown(int code, Datum arg)
{
	/* Don't try to dump during a crash. */
	elog(LOG,"pgss_shmem_shutdown");
	if (code)
		return;

	pgsmStateLocal.shared_pgssState = NULL;
	/* Safety check ... shouldn't get here unless shmem is set up. */
	if (!IsHashInitialize())
		return;
}

static void
pgsm_proc_exit(int code, Datum arg)
{
	Assert(pgsmStateLocal.dsa);
	dshash_detach(pgsmStateLocal.shared_hash);
	pgsmStateLocal.shared_hash = NULL;
	dsa_detach(pgsmStateLocal.dsa);
	pgsmStateLocal.dsa = NULL;
}

pgssEntry *
hash_entry_alloc(pgssSharedState *pgss, pgssHashKey *key, int encoding)
{
	pgssEntry  *entry = NULL;
	bool		found = false;

	/* Find or create an entry with desired hash code */
	entry = (pgssEntry *) dshash_find_or_insert(pgsmStateLocal.shared_hash, key, &found);
	// entry = (pgssEntry *) hash_search(pgss_hash, key, HASH_ENTER_NULL, &found);
	if (entry == NULL)
		elog(DEBUG1, "hash_entry_alloc: OUT OF MEMORY");
	else if (!found)
	{
		pgss->bucket_entry[pg_atomic_read_u64(&pgss->current_wbucket)]++;
		/* New entry, initialize it */
		/* reset the statistics */
		memset(&entry->counters, 0, sizeof(Counters));
		/* set the appropriate initial usage count */
		/* re-initialize the mutex each time ... we assume no one using it */
		SpinLockInit(&entry->mutex);
		/* ... and don't forget the query text metadata */
		entry->encoding = encoding;
	}
	dshash_release_lock(pgsmStateLocal.shared_hash, entry);

	return entry;
}

/*
 * Prepare resources for using the new bucket:
 *    - Deallocate finished hash table entries in new_bucket_id (entries whose
 *      state is PGSS_FINISHED or PGSS_FINISHED).
 *    - Clear query buffer for new_bucket_id.
 *    - If old_bucket_id != -1, move all pending hash table entries in
 *      old_bucket_id to the new bucket id, also move pending queries from the
 *      previous query buffer (query_buffer[old_bucket_id]) to the new one
 *      (query_buffer[new_bucket_id]).
 *
 * Caller must hold an exclusive lock on pgss->lock.
 */
void
hash_entry_dealloc(int new_bucket_id, int old_bucket_id, unsigned char *query_buffer)
{
	dshash_seq_status hstat;
	pgssEntry  *entry = NULL;
	/* Store pending query ids from the previous bucket. */
	List	   *pending_entries = NIL;
	ListCell   *pending_entry;

	if (!pgsmStateLocal.shared_hash)
		return;

	/* Iterate over the hash table. */
	dshash_seq_init(&hstat, pgsmStateLocal.shared_hash, true);

	while ((entry = dshash_seq_next(&hstat)) != NULL)
	{
		dsa_pointer pdsa;

		/*
		 * Remove all entries if new_bucket_id == -1. Otherwise remove entry
		 * in new_bucket_id if it has finished already.
		 */
		if (new_bucket_id < 0 ||
			(entry->key.bucket_id == new_bucket_id &&
			 (entry->counters.state == PGSS_FINISHED || entry->counters.state == PGSS_ERROR)))
		{
			pdsa = entry->query_pos;
			dsa_pointer parent_qdsa = entry->counters.info.parent_query;
			dshash_delete_current(&hstat);
			dsa_free(pgsmStateLocal.dsa, pdsa);

			if (DsaPointerIsValid(parent_qdsa))
				dsa_free(pgsmStateLocal.dsa, parent_qdsa);

		}

		/*
		 * If we detect a pending query residing in the previous bucket id, we
		 * add it to a list of pending elements to be moved to the new bucket
		 * id. Can't update the hash table while iterating it inside this
		 * loop, as this may introduce all sort of problems.
		 */
		if (old_bucket_id != -1 && entry->key.bucket_id == old_bucket_id)
		{
			if (entry->counters.state == PGSS_PARSE ||
				entry->counters.state == PGSS_PLAN ||
				entry->counters.state == PGSS_EXEC)
			{
				pgssEntry  *bkp_entry = malloc(sizeof(pgssEntry));

				if (!bkp_entry)
				{
					elog(DEBUG1, "hash_entry_dealloc: out of memory");

					/*
					 * No memory, If the entry has calls > 1 then we change
					 * the state to finished, as the pending query will likely
					 * finish execution during the new bucket time window. The
					 * pending query will vanish in this case, can't list it
					 * until it completes.
					 *
					 * If there is only one call to the query and it's
					 * pending, remove the entry from the previous bucket and
					 * allow it to finish in the new bucket, in order to avoid
					 * the query living in the old bucket forever.
					 */
					if (entry->counters.calls.calls > 1)
						entry->counters.state = PGSS_FINISHED;
					else
					{
						pdsa = entry->query_pos;
						dshash_delete_current(&hstat);
						dsa_free(pgsmStateLocal.dsa, pdsa);
					}
					continue;
				}

				/* Save key/data from the previous entry. */
				memcpy(bkp_entry, entry, sizeof(pgssEntry));

				/* Update key to use the new bucket id. */
				bkp_entry->key.bucket_id = new_bucket_id;

				/* Add the entry to a list of nodes to be processed later. */
				pending_entries = lappend(pending_entries, bkp_entry);

				/*
				 * If the entry has calls > 1 then we change the state to
				 * finished in the previous bucket, as the pending query will
				 * likely finish execution during the new bucket time window.
				 * Can't remove it from the previous bucket as it may have
				 * many calls and we would lose the query statistics.
				 *
				 * If there is only one call to the query and it's pending,
				 * remove the entry from the previous bucket and allow it to
				 * finish in the new bucket, in order to avoid the query
				 * living in the old bucket forever.
				 */
				if (entry->counters.calls.calls > 1)
					entry->counters.state = PGSS_FINISHED;
				else
				{
					pdsa = entry->query_pos;
					dshash_delete_current(&hstat);
					dsa_free(pgsmStateLocal.dsa, pdsa);
				}
			}
		}
	}
	dshash_seq_term(&hstat);
	/*
	 * Iterate over the list of pending queries in order to add them back to
	 * the hash table with the updated bucket id.
	 */
	foreach(pending_entry, pending_entries)
	{
		bool		found = false;
		pgssEntry  *new_entry;
		pgssEntry  *old_entry = (pgssEntry *) lfirst(pending_entry);


		new_entry = (pgssEntry *) dshash_find_or_insert(pgsmStateLocal.shared_hash, &old_entry->key, &found);
		if (new_entry == NULL)
			elog(DEBUG1, "%s", "pg_stat_monitor: out of memory");
		else if (!found)
		{
			/* Restore counters and other data. */
			new_entry->counters = old_entry->counters;
			SpinLockInit(&new_entry->mutex);
			new_entry->encoding = old_entry->encoding;
			new_entry->query_pos = old_entry->query_pos;
		}
		free(old_entry);
		dshash_release_lock(pgsmStateLocal.shared_hash, entry);

	}

	list_free(pending_entries);
}

/*
 * Release all entries.
 */
void
hash_entry_reset()
{
	pgssSharedState *pgss = pgsm_get_ss();
	dshash_seq_status hstat;
	pgssEntry  *entry;

	LWLockAcquire(pgss->lock, LW_EXCLUSIVE);

	dshash_seq_init(&hstat, pgsmStateLocal.shared_hash, true);

	while ((entry = dshash_seq_next(&hstat)) != NULL)
	{
		dsa_pointer pdsa = entry->query_pos;
		dshash_delete_current(&hstat);
		dsa_free(pgsmStateLocal.dsa, pdsa);
	}

	dshash_seq_term(&hstat);

	pg_atomic_write_u64(&pgss->current_wbucket, 0);
	LWLockRelease(pgss->lock);
}

bool
IsHashInitialize(void)
{
	return (pgsmStateLocal.shared_pgssState != NULL);
}