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pg_qualstats.c
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pg_qualstats.c
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/*-------------------------------------------------------------------------
*
* pg_qualstats.c
* Track frequently used quals.
*
* This extension works by installing a hooks on executor.
* The ExecutorStart hook will enable some instrumentation for the
* queries (INSTRUMENT_ROWS and INSTRUMENT_BUFFERS).
*
* The ExecutorEnd hook will look for every qual in the query, and
* stores the quals of the form:
* - EXPR OPERATOR CONSTANT
* - EXPR OPERATOR EXPR
*
* If pg_stat_statements is available, the statistics will be
* aggregated by queryid, and a not-normalized statement will be
* stored for each different queryid. This can allow third part tools
* to do some work on a real query easily.
*
* The implementation is heavily inspired by pg_stat_statements
*
* Copyright (c) 2014,2017 Ronan Dunklau
* Copyright (c) 2018-2024, The Powa-Team
*-------------------------------------------------------------------------
*/
#include <limits.h>
#include <math.h>
#include "postgres.h"
#include "access/hash.h"
#include "access/htup_details.h"
#if PG_VERSION_NUM >= 90600
#include "access/parallel.h"
#endif
#if PG_VERSION_NUM >= 100000 && PG_VERSION_NUM < 110000
#include "catalog/pg_authid.h"
#endif
#if PG_VERSION_NUM >= 110000
#include "catalog/pg_authid_d.h"
#endif
#include "catalog/pg_class.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_type.h"
#include "commands/dbcommands.h"
#if PG_VERSION_NUM >= 150000
#include "common/pg_prng.h"
#endif
#include "fmgr.h"
#include "funcapi.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "nodes/execnodes.h"
#include "nodes/nodeFuncs.h"
#include "nodes/makefuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/planner.h"
#include "parser/analyze.h"
#include "parser/parse_node.h"
#include "parser/parsetree.h"
#if PG_VERSION_NUM >= 150000
#include "postmaster/autovacuum.h"
#endif
#include "postmaster/postmaster.h"
#if PG_VERSION_NUM >= 150000
#include "replication/walsender.h"
#endif
#include "storage/ipc.h"
#include "storage/lwlock.h"
#if PG_VERSION_NUM >= 100000
#include "storage/shmem.h"
#endif
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/tuplestore.h"
PG_MODULE_MAGIC;
#define PGQS_NAME_COLUMNS 7 /* number of column added when using
* pg_qualstats_column SRF */
#define PGQS_USAGE_DEALLOC_PERCENT 5 /* free this % of entries at once */
#define PGQS_MAX_DEFAULT 1000 /* default pgqs_max value */
#define PGQS_MAX_LOCAL_ENTRIES (pgqs_max * 0.2) /* do not track more of
* 20% of possible entries
* in shared mem */
#define PGQS_CONSTANT_SIZE 80 /* Truncate constant representation at 80 */
#define PGQS_FLAGS (INSTRUMENT_ROWS|INSTRUMENT_BUFFERS)
#define PGQS_RATIO 0
#define PGQS_NUM 1
#define PGQS_LWL_ACQUIRE(lock, mode) if (!pgqs_backend) { \
LWLockAcquire(lock, mode); \
}
#define PGQS_LWL_RELEASE(lock) if (!pgqs_backend) { \
LWLockRelease(lock); \
}
#if PG_VERSION_NUM < 170000
#define MyProcNumber MyBackendId
#define ParallelLeaderProcNumber ParallelLeaderBackendId
#endif
#if PG_VERSION_NUM < 140000
#define ParallelLeaderBackendId ParallelMasterBackendId
#endif
/*
* Extension version number, for supporting older extension versions' objects
*/
typedef enum pgqsVersion
{
PGQS_V1_0 = 0,
PGQS_V2_0
} pgqsVersion;
/*---- Function declarations ----*/
extern PGDLLEXPORT void _PG_init(void);
extern PGDLLEXPORT Datum pg_qualstats_reset(PG_FUNCTION_ARGS);
extern PGDLLEXPORT Datum pg_qualstats(PG_FUNCTION_ARGS);
extern PGDLLEXPORT Datum pg_qualstats_2_0(PG_FUNCTION_ARGS);
extern PGDLLEXPORT Datum pg_qualstats_names(PG_FUNCTION_ARGS);
extern PGDLLEXPORT Datum pg_qualstats_names_2_0(PG_FUNCTION_ARGS);
static Datum pg_qualstats_common(PG_FUNCTION_ARGS, pgqsVersion api_version,
bool include_names);
extern PGDLLEXPORT Datum pg_qualstats_example_query(PG_FUNCTION_ARGS);
extern PGDLLEXPORT Datum pg_qualstats_example_queries(PG_FUNCTION_ARGS);
PG_FUNCTION_INFO_V1(pg_qualstats_reset);
PG_FUNCTION_INFO_V1(pg_qualstats);
PG_FUNCTION_INFO_V1(pg_qualstats_2_0);
PG_FUNCTION_INFO_V1(pg_qualstats_names);
PG_FUNCTION_INFO_V1(pg_qualstats_names_2_0);
PG_FUNCTION_INFO_V1(pg_qualstats_example_query);
PG_FUNCTION_INFO_V1(pg_qualstats_example_queries);
static void pgqs_backend_mode_startup(void);
#if PG_VERSION_NUM >= 150000
static void pgqs_shmem_request(void);
#endif
static void pgqs_shmem_startup(void);
static void pgqs_ExecutorStart(QueryDesc *queryDesc, int eflags);
static void pgqs_ExecutorRun(QueryDesc *queryDesc,
ScanDirection direction,
#if PG_VERSION_NUM >= 90600
uint64 count
#else
long count
#endif
#if PG_VERSION_NUM >= 100000
, bool execute_once
#endif
);
static void pgqs_ExecutorFinish(QueryDesc *queryDesc);
static void pgqs_ExecutorEnd(QueryDesc *queryDesc);
static ExecutorStart_hook_type prev_ExecutorStart = NULL;
static ExecutorRun_hook_type prev_ExecutorRun = NULL;
static ExecutorFinish_hook_type prev_ExecutorFinish = NULL;
static ExecutorEnd_hook_type prev_ExecutorEnd = NULL;
#if PG_VERSION_NUM >= 150000
static shmem_request_hook_type prev_shmem_request_hook = NULL;
#endif
static shmem_startup_hook_type prev_shmem_startup_hook = NULL;
static uint32 pgqs_hash_fn(const void *key, Size keysize);
#if PG_VERSION_NUM < 90500
static uint32 pgqs_uint32_hashfn(const void *key, Size keysize);
#endif
static bool pgqs_backend = false;
static int pgqs_query_size;
static int pgqs_max = PGQS_MAX_DEFAULT; /* max # statements to track */
static bool pgqs_track_pgcatalog; /* track queries on pg_catalog */
static bool pgqs_resolve_oids; /* resolve oids */
static bool pgqs_enabled;
static bool pgqs_track_constants;
static double pgqs_sample_rate;
static int pgqs_min_err_ratio;
static int pgqs_min_err_num;
static int query_is_sampled; /* Is the current query sampled, per backend */
static int nesting_level = 0; /* Current nesting depth of ExecutorRun calls */
static bool pgqs_assign_sample_rate_check_hook(double *newval, void **extra, GucSource source);
#if PG_VERSION_NUM > 90600
static void pgqs_set_query_sampled(bool sample);
#endif
static bool pgqs_is_query_sampled(void);
/*---- Data structures declarations ----*/
typedef struct pgqsSharedState
{
#if PG_VERSION_NUM >= 90400
LWLock *lock; /* protects counters hashtable
* search/modification */
LWLock *querylock; /* protects query hashtable
* search/modification */
#else
LWLockId lock; /* protects counters hashtable
* search/modification */
LWLockId querylock; /* protects query hashtable
* search/modification */
#endif
#if PG_VERSION_NUM >= 90600
LWLock *sampledlock; /* protects sampled array search/modification */
bool sampled[FLEXIBLE_ARRAY_MEMBER]; /* should we sample this
* query? */
#endif
} pgqsSharedState;
/* Since cff440d368, queryid becomes a uint64 internally. */
#if PG_VERSION_NUM >= 110000
typedef uint64 pgqs_queryid;
#else
typedef uint32 pgqs_queryid;
#endif
typedef struct pgqsHashKey
{
Oid userid; /* user OID */
Oid dbid; /* database OID */
pgqs_queryid queryid; /* query identifier (if set by another plugin */
uint32 uniquequalnodeid; /* Hash of the const */
uint32 uniquequalid; /* Hash of the parent, including the consts */
char evaltype; /* Evaluation type. Can be 'f' to mean a qual
* executed after a scan, or 'i' for an
* indexqual */
} pgqsHashKey;
typedef struct pgqsNames
{
NameData rolname;
NameData datname;
NameData lrelname;
NameData lattname;
NameData opname;
NameData rrelname;
NameData rattname;
} pgqsNames;
typedef struct pgqsEntry
{
pgqsHashKey key;
Oid lrelid; /* LHS relation OID or NULL if not var */
AttrNumber lattnum; /* LHS attribute Number or NULL if not var */
Oid opoid; /* Operator OID */
Oid rrelid; /* RHS relation OID or NULL if not var */
AttrNumber rattnum; /* RHS attribute Number or NULL if not var */
char constvalue[PGQS_CONSTANT_SIZE]; /* Textual representation of
* the right hand constant, if
* any */
uint32 qualid; /* Hash of the parent AND expression if any, 0
* otherwise. */
uint32 qualnodeid; /* Hash of the node itself */
int64 count; /* # of operator execution */
int64 nbfiltered; /* # of lines discarded by the operator */
int position; /* content position in query text */
double usage; /* # of qual execution, used for deallocation */
double min_err_estim[2]; /* min estimation error ratio and num */
double max_err_estim[2]; /* max estimation error ratio and num */
double mean_err_estim[2]; /* mean estimation error ratio and num */
double sum_err_estim[2]; /* sum of variances in estimation error
* ratio and num */
int64 occurences; /* # of qual execution, 1 per query */
} pgqsEntry;
typedef struct pgqsEntryWithNames
{
pgqsEntry entry;
pgqsNames names;
} pgqsEntryWithNames;
typedef struct pgqsQueryStringHashKey
{
pgqs_queryid queryid;
} pgqsQueryStringHashKey;
typedef struct pgqsQueryStringEntry
{
pgqsQueryStringHashKey key;
/*
* Imperatively at the end of the struct This is actually of length
* query_size, which is track_activity_query_size
*/
char querytext[1];
} pgqsQueryStringEntry;
/*
* Transient state of the query tree walker - for the meaning of the counters,
* see pgqsEntry comments.
*/
typedef struct pgqsWalkerContext
{
pgqs_queryid queryId;
List *rtable;
PlanState *planstate;
PlanState *inner_planstate;
PlanState *outer_planstate;
List *outer_tlist;
List *inner_tlist;
List *index_tlist;
uint32 qualid;
uint32 uniquequalid; /* Hash of the parent, including the consts */
int64 count;
int64 nbfiltered;
double err_estim[2];
int nentries; /* number of entries found so far */
char evaltype;
const char *querytext;
} pgqsWalkerContext;
static bool pgqs_whereclause_tree_walker(Node *node, pgqsWalkerContext *query);
static pgqsEntry *pgqs_process_opexpr(OpExpr *expr, pgqsWalkerContext *context);
static pgqsEntry *pgqs_process_scalararrayopexpr(ScalarArrayOpExpr *expr, pgqsWalkerContext *context);
static pgqsEntry *pgqs_process_booltest(BooleanTest *expr, pgqsWalkerContext *context);
static void pgqs_collectNodeStats(PlanState *planstate, List *ancestors, pgqsWalkerContext *context);
static void pgqs_collectMemberNodeStats(int nplans, PlanState **planstates, List *ancestors, pgqsWalkerContext *context);
static void pgqs_collectSubPlanStats(List *plans, List *ancestors, pgqsWalkerContext *context);
static uint32 hashExpr(Expr *expr, pgqsWalkerContext *context, bool include_const);
static void exprRepr(Expr *expr, StringInfo buffer, pgqsWalkerContext *context, bool include_const);
static void pgqs_set_planstates(PlanState *planstate, pgqsWalkerContext *context);
static Expr *pgqs_resolve_var(Var *var, pgqsWalkerContext *context);
static void pgqs_entry_dealloc(void);
static inline void pgqs_entry_init(pgqsEntry *entry);
static inline void pgqs_entry_copy_raw(pgqsEntry *dest, pgqsEntry *src);
static void pgqs_entry_err_estim(pgqsEntry *e, double *err_estim, int64 occurences);
static void pgqs_queryentry_dealloc(void);
static void pgqs_localentry_dealloc(int nvictims);
static void pgqs_fillnames(pgqsEntryWithNames *entry);
static Size pgqs_memsize(void);
#if PG_VERSION_NUM >= 90600
static Size pgqs_sampled_array_size(void);
#endif
/* Global Hash */
static HTAB *pgqs_hash = NULL;
static HTAB *pgqs_query_examples_hash = NULL;
static pgqsSharedState *pgqs = NULL;
/* Local Hash */
static HTAB *pgqs_localhash = NULL;
void
_PG_init(void)
{
if (!process_shared_preload_libraries_in_progress)
{
elog(WARNING, "Without shared_preload_libraries, only current backend stats will be available.");
pgqs_backend = true;
}
else
{
pgqs_backend = false;
#if PG_VERSION_NUM >= 150000
prev_shmem_request_hook = shmem_request_hook;
shmem_request_hook = pgqs_shmem_request;
#endif
prev_shmem_startup_hook = shmem_startup_hook;
shmem_startup_hook = pgqs_shmem_startup;
}
prev_ExecutorStart = ExecutorStart_hook;
ExecutorStart_hook = pgqs_ExecutorStart;
prev_ExecutorRun = ExecutorRun_hook;
ExecutorRun_hook = pgqs_ExecutorRun;
prev_ExecutorFinish = ExecutorFinish_hook;
ExecutorFinish_hook = pgqs_ExecutorFinish;
prev_ExecutorEnd = ExecutorEnd_hook;
ExecutorEnd_hook = pgqs_ExecutorEnd;
DefineCustomBoolVariable("pg_qualstats.enabled",
"Enable / Disable pg_qualstats",
NULL,
&pgqs_enabled,
true,
PGC_USERSET,
0,
NULL,
NULL,
NULL);
DefineCustomBoolVariable("pg_qualstats.track_constants",
"Enable / Disable pg_qualstats constants tracking",
NULL,
&pgqs_track_constants,
true,
PGC_USERSET,
0,
NULL,
NULL,
NULL);
DefineCustomIntVariable("pg_qualstats.max",
"Sets the maximum number of statements tracked by pg_qualstats.",
NULL,
&pgqs_max,
PGQS_MAX_DEFAULT,
100,
INT_MAX,
pgqs_backend ? PGC_USERSET : PGC_POSTMASTER,
0,
NULL,
NULL,
NULL);
if (!pgqs_backend)
DefineCustomBoolVariable("pg_qualstats.resolve_oids",
"Store names alongside the oid. Eats MUCH more space!",
NULL,
&pgqs_resolve_oids,
false,
PGC_POSTMASTER,
0,
NULL,
NULL,
NULL);
DefineCustomBoolVariable("pg_qualstats.track_pg_catalog",
"Track quals on system catalogs too.",
NULL,
&pgqs_track_pgcatalog,
false,
PGC_USERSET,
0,
NULL,
NULL,
NULL);
DefineCustomRealVariable("pg_qualstats.sample_rate",
"Sampling rate. 1 means every query, 0.2 means 1 in five queries",
NULL,
&pgqs_sample_rate,
-1,
-1,
1,
PGC_USERSET,
0,
pgqs_assign_sample_rate_check_hook,
NULL,
NULL);
DefineCustomIntVariable("pg_qualstats.min_err_estimate_ratio",
"Error estimation ratio threshold to save quals",
NULL,
&pgqs_min_err_ratio,
0,
0,
INT_MAX,
PGC_USERSET,
0,
NULL,
NULL,
NULL);
DefineCustomIntVariable("pg_qualstats.min_err_estimate_num",
"Error estimation num threshold to save quals",
NULL,
&pgqs_min_err_num,
0,
0,
INT_MAX,
PGC_USERSET,
0,
NULL,
NULL,
NULL);
EmitWarningsOnPlaceholders("pg_qualstats");
parse_int(GetConfigOption("track_activity_query_size", false, false),
&pgqs_query_size, 0, NULL);
if (!pgqs_backend)
{
#if PG_VERSION_NUM < 150000
RequestAddinShmemSpace(pgqs_memsize());
#if PG_VERSION_NUM >= 90600
RequestNamedLWLockTranche("pg_qualstats", 3);
#else
RequestAddinLWLocks(2);
#endif /* pg9.6+ */
#endif /* pg15- */
}
else
pgqs_backend_mode_startup();
}
/*
* Check that the sample ratio is in the correct interval
*/
static bool
pgqs_assign_sample_rate_check_hook(double *newval, void **extra, GucSource source)
{
double val = *newval;
if ((val < 0 && val != -1) || (val > 1))
return false;
if (val == -1)
*newval = 1. / MaxConnections;
return true;
}
#if PG_VERSION_NUM >= 90600
static void
pgqs_set_query_sampled(bool sample)
{
/* the decisions should only be made in leader */
Assert(!IsParallelWorker());
/* not supported in backend mode */
if (pgqs_backend)
return;
/* in worker processes we need to get the info from shared memory */
LWLockAcquire(pgqs->sampledlock, LW_EXCLUSIVE);
pgqs->sampled[MyProcNumber] = sample;
LWLockRelease(pgqs->sampledlock);
}
#endif
static bool
pgqs_is_query_sampled(void)
{
#if PG_VERSION_NUM >= 90600
bool sampled;
/* in leader we can just check the global variable */
if (!IsParallelWorker())
return query_is_sampled;
/* not supported in backend mode */
if (pgqs_backend)
return false;
/* in worker processes we need to get the info from shared memory */
PGQS_LWL_ACQUIRE(pgqs->sampledlock, LW_SHARED);
sampled = pgqs->sampled[ParallelLeaderProcNumber];
PGQS_LWL_RELEASE(pgqs->sampledlock);
return sampled;
#else
return query_is_sampled;
#endif
}
/*
* Do catalog search to replace oids with corresponding objects name
*/
void
pgqs_fillnames(pgqsEntryWithNames *entry)
{
#if PG_VERSION_NUM >= 110000
#define GET_ATTNAME(r, a) get_attname(r, a, false)
#else
#define GET_ATTNAME(r, a) get_attname(r, a)
#endif
#if PG_VERSION_NUM >= 90500
namestrcpy(&(entry->names.rolname), GetUserNameFromId(entry->entry.key.userid, true));
#else
namestrcpy(&(entry->names.rolname), GetUserNameFromId(entry->entry.key.userid));
#endif
namestrcpy(&(entry->names.datname), get_database_name(entry->entry.key.dbid));
if (entry->entry.lrelid != InvalidOid)
{
namestrcpy(&(entry->names.lrelname),
get_rel_name(entry->entry.lrelid));
namestrcpy(&(entry->names.lattname),
GET_ATTNAME(entry->entry.lrelid, entry->entry.lattnum));
}
if (entry->entry.opoid != InvalidOid)
namestrcpy(&(entry->names.opname), get_opname(entry->entry.opoid));
if (entry->entry.rrelid != InvalidOid)
{
namestrcpy(&(entry->names.rrelname),
get_rel_name(entry->entry.rrelid));
namestrcpy(&(entry->names.rattname),
GET_ATTNAME(entry->entry.rrelid, entry->entry.rattnum));
}
#undef GET_ATTNAME
}
/*
* Request rows and buffers instrumentation if pgqs is enabled
*/
static void
pgqs_ExecutorStart(QueryDesc *queryDesc, int eflags)
{
/* Setup instrumentation */
if (pgqs_enabled)
{
/*
* For rate sampling, randomly choose top-level statement. Either all
* nested statements will be explained or none will.
*/
if (nesting_level == 0
#if PG_VERSION_NUM >= 90600
&& (!IsParallelWorker())
#endif
)
{
#if PG_VERSION_NUM >= 150000
query_is_sampled = (pg_prng_double(&pg_global_prng_state) <
pgqs_sample_rate);
#else
query_is_sampled = (random() <= (MAX_RANDOM_VALUE *
pgqs_sample_rate));
#endif
#if PG_VERSION_NUM >= 90600
pgqs_set_query_sampled(query_is_sampled);
#endif
}
if (pgqs_is_query_sampled())
queryDesc->instrument_options |= PGQS_FLAGS;
}
if (prev_ExecutorStart)
prev_ExecutorStart(queryDesc, eflags);
else
standard_ExecutorStart(queryDesc, eflags);
}
/*
* ExecutorRun hook: all we need do is track nesting depth
*/
static void
pgqs_ExecutorRun(QueryDesc *queryDesc,
ScanDirection direction,
#if PG_VERSION_NUM >= 90600
uint64 count
#else
long count
#endif
#if PG_VERSION_NUM >= 100000
,bool execute_once
#endif
)
{
nesting_level++;
PG_TRY();
{
if (prev_ExecutorRun)
#if PG_VERSION_NUM >= 100000
prev_ExecutorRun(queryDesc, direction, count, execute_once);
#else
prev_ExecutorRun(queryDesc, direction, count);
#endif
else
#if PG_VERSION_NUM >= 100000
standard_ExecutorRun(queryDesc, direction, count, execute_once);
#else
standard_ExecutorRun(queryDesc, direction, count);
#endif
nesting_level--;
}
PG_CATCH();
{
nesting_level--;
PG_RE_THROW();
}
PG_END_TRY();
}
/*
* ExecutorFinish hook: all we need do is track nesting depth
*/
static void
pgqs_ExecutorFinish(QueryDesc *queryDesc)
{
nesting_level++;
PG_TRY();
{
if (prev_ExecutorFinish)
prev_ExecutorFinish(queryDesc);
else
standard_ExecutorFinish(queryDesc);
nesting_level--;
}
PG_CATCH();
{
nesting_level--;
PG_RE_THROW();
}
PG_END_TRY();
}
/*
* Save a non normalized query for the queryid if no one already exists, and
* do all the stat collecting job
*/
static void
pgqs_ExecutorEnd(QueryDesc *queryDesc)
{
pgqsQueryStringHashKey queryKey;
bool found;
if ((pgqs || pgqs_backend) && pgqs_enabled && pgqs_is_query_sampled()
#if PG_VERSION_NUM >= 90600
&& (!IsParallelWorker())
#endif
/*
* multiple ExecutorStart/ExecutorEnd can be interleaved, so when sampling
* is activated there's no guarantee that pgqs_is_query_sampled() will
* only detect queries that were actually sampled (thus having the
* required instrumentation set up). To avoid such cases, we double check
* that we have the required instrumentation set up. That won't exactly
* detect the sampled queries, but that should be close enough and avoid
* adding to much complexity.
*/
&& (queryDesc->instrument_options & PGQS_FLAGS) == PGQS_FLAGS
)
{
HASHCTL info;
pgqsEntry *localentry;
HASH_SEQ_STATUS local_hash_seq;
/* We need to switch to the per-query memory context */
MemoryContext oldcxt = MemoryContextSwitchTo(queryDesc->estate->es_query_cxt);
pgqsWalkerContext *context = palloc(sizeof(pgqsWalkerContext));
context->queryId = queryDesc->plannedstmt->queryId;
context->rtable = queryDesc->plannedstmt->rtable;
context->count = 0;
context->qualid = 0;
context->uniquequalid = 0;
context->nbfiltered = 0;
context->evaltype = 0;
context->nentries = 0;
context->querytext = queryDesc->sourceText;
queryKey.queryid = context->queryId;
/* keep an unormalized query example for each queryid if needed */
if (pgqs_track_constants)
{
/* Lookup the hash table entry with a shared lock. */
PGQS_LWL_ACQUIRE(pgqs->querylock, LW_SHARED);
hash_search_with_hash_value(pgqs_query_examples_hash, &queryKey,
context->queryId,
HASH_FIND, &found);
/* Create the new entry if not present */
if (!found)
{
pgqsQueryStringEntry *queryEntry;
bool excl_found;
/* Need exclusive lock to add a new hashtable entry - promote */
PGQS_LWL_RELEASE(pgqs->querylock);
PGQS_LWL_ACQUIRE(pgqs->querylock, LW_EXCLUSIVE);
while (hash_get_num_entries(pgqs_query_examples_hash) >= pgqs_max)
pgqs_queryentry_dealloc();
queryEntry = (pgqsQueryStringEntry *) hash_search_with_hash_value(pgqs_query_examples_hash, &queryKey,
context->queryId,
HASH_ENTER, &excl_found);
/* Make sure it wasn't added by another backend */
if (!excl_found)
strncpy(queryEntry->querytext, context->querytext, pgqs_query_size);
}
PGQS_LWL_RELEASE(pgqs->querylock);
}
/* create local hash table if it hasn't been created yet */
if (!pgqs_localhash)
{
memset(&info, 0, sizeof(info));
info.keysize = sizeof(pgqsHashKey);
if (pgqs_resolve_oids)
info.entrysize = sizeof(pgqsEntryWithNames);
else
info.entrysize = sizeof(pgqsEntry);
info.hash = pgqs_hash_fn;
pgqs_localhash = hash_create("pgqs_localhash",
50,
&info,
HASH_ELEM | HASH_FUNCTION);
}
/* retrieve quals informations, main work starts from here */
pgqs_collectNodeStats(queryDesc->planstate, NIL, context);
/* if any quals found, store them in shared memory */
if (context->nentries)
{
/*
* Before acquiring exlusive lwlock, check if there's enough room
* to store local hash. Also, do not remove more than 20% of
* maximum number of entries in shared memory (wether they are
* used or not). This should not happen since we shouldn't store
* that much entries in localhash in the first place.
*/
int nvictims = hash_get_num_entries(pgqs_localhash) -
PGQS_MAX_LOCAL_ENTRIES;
if (nvictims > 0)
pgqs_localentry_dealloc(nvictims);
PGQS_LWL_ACQUIRE(pgqs->lock, LW_EXCLUSIVE);
while (hash_get_num_entries(pgqs_hash) +
hash_get_num_entries(pgqs_localhash) >= pgqs_max)
pgqs_entry_dealloc();
hash_seq_init(&local_hash_seq, pgqs_localhash);
while ((localentry = hash_seq_search(&local_hash_seq)) != NULL)
{
pgqsEntry *newEntry = (pgqsEntry *) hash_search(pgqs_hash,
&localentry->key,
HASH_ENTER, &found);
if (!found)
{
/* raw copy the local entry */
pgqs_entry_copy_raw(newEntry, localentry);
}
else
{
/* only update counters value */
newEntry->count += localentry->count;
newEntry->nbfiltered += localentry->nbfiltered;
newEntry->usage += localentry->usage;
/* compute estimation error min, max, mean and variance */
pgqs_entry_err_estim(newEntry, localentry->mean_err_estim,
localentry->occurences);
}
/* cleanup local hash */
hash_search(pgqs_localhash, &localentry->key, HASH_REMOVE, NULL);
}
PGQS_LWL_RELEASE(pgqs->lock);
}
MemoryContextSwitchTo(oldcxt);
}
if (prev_ExecutorEnd)
prev_ExecutorEnd(queryDesc);
else
standard_ExecutorEnd(queryDesc);
}
/*
* qsort comparator for sorting into increasing usage order
*/
static int
entry_cmp(const void *lhs, const void *rhs)
{
double l_usage = (*(pgqsEntry *const *) lhs)->usage;
double r_usage = (*(pgqsEntry *const *) rhs)->usage;
if (l_usage < r_usage)
return -1;
else if (l_usage > r_usage)
return +1;
else
return 0;
}
/*
* Deallocate least used entries.
* Caller must hold an exlusive lock on pgqs->lock
*/
static void
pgqs_entry_dealloc(void)
{
HASH_SEQ_STATUS hash_seq;
pgqsEntry **entries;
pgqsEntry *entry;
int nvictims;
int i;
int base_size;
/*
* Sort entries by usage and deallocate PGQS_USAGE_DEALLOC_PERCENT of
* them. While we're scanning the table, apply the decay factor to the
* usage values.
* pgqs_resolve_oids is irrelevant here as the array stores pointers
* instead of entries. The struct member used for the sort are part of
* pgqsEntry.
*/
base_size = sizeof(pgqsEntry *);
entries = palloc(hash_get_num_entries(pgqs_hash) * base_size);
i = 0;
hash_seq_init(&hash_seq, pgqs_hash);
while ((entry = hash_seq_search(&hash_seq)) != NULL)
{
entries[i++] = entry;
entry->usage *= 0.99;
}
qsort(entries, i, base_size, entry_cmp);
nvictims = Max(10, i * PGQS_USAGE_DEALLOC_PERCENT / 100);
nvictims = Min(nvictims, i);
for (i = 0; i < nvictims; i++)
hash_search(pgqs_hash, &entries[i]->key, HASH_REMOVE, NULL);
pfree(entries);
}
/* Initialize all non-key fields of the given entry. */
static inline void
pgqs_entry_init(pgqsEntry *entry)
{
/* Note that pgqsNames if needed will be explicitly filled after this */
memset(&(entry->lrelid), 0, sizeof(pgqsEntry) - sizeof(pgqsHashKey));
}
/* Copy non-key and non-name fields from the given entry */
static inline void
pgqs_entry_copy_raw(pgqsEntry *dest, pgqsEntry *src)
{
/* Note that pgqsNames if needed will be explicitly filled after this */
memcpy(&(dest->lrelid),
&(src->lrelid),
(sizeof(pgqsEntry) - sizeof(pgqsHashKey)));
}
/*
* Accurately compute estimation error ratio and num variance using Welford's
* method. See <http://www.johndcook.com/blog/standard_deviation/>
* Also maintain min and max values.
*/
static void
pgqs_entry_err_estim(pgqsEntry *e, double *err_estim, int64 occurences)
{
int i;
e->occurences += occurences;
for (i = 0; i < 2; i++)
{
if ((e->occurences - occurences) == 0)
{
e->min_err_estim[i] = err_estim[i];
e->max_err_estim[i] = err_estim[i];
e->mean_err_estim[i] = err_estim[i];
}
else
{
double old_err = e->mean_err_estim[i];
e->mean_err_estim[i] +=
(err_estim[i] - old_err) / e->occurences;
e->sum_err_estim[i] +=
(err_estim[i] - old_err) * (err_estim[i] - e->mean_err_estim[i]);
}
/* calculate min/max counters */
if (e->min_err_estim[i] > err_estim[i])
e->min_err_estim[i] = err_estim[i];
if (e->max_err_estim[i] < err_estim[i])
e->max_err_estim[i] = err_estim[i];
}
}
/*
* Deallocate the first example query.
* Caller must hold an exlusive lock on pgqs->querylock
*/
static void
pgqs_queryentry_dealloc(void)
{
HASH_SEQ_STATUS hash_seq;
pgqsQueryStringEntry *entry;
hash_seq_init(&hash_seq, pgqs_query_examples_hash);
entry = hash_seq_search(&hash_seq);