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postgresql/src/backend/executor/nodeMemoize.c

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/*-------------------------------------------------------------------------
*
* nodeMemoize.c
* Routines to handle caching of results from parameterized nodes
*
* Portions Copyright (c) 2021-2023, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/executor/nodeMemoize.c
*
* Memoize nodes are intended to sit above parameterized nodes in the plan
* tree in order to cache results from them. The intention here is that a
* repeat scan with a parameter value that has already been seen by the node
* can fetch tuples from the cache rather than having to re-scan the outer
* node all over again. The query planner may choose to make use of one of
* these when it thinks rescans for previously seen values are likely enough
* to warrant adding the additional node.
*
* The method of cache we use is a hash table. When the cache fills, we never
* spill tuples to disk, instead, we choose to evict the least recently used
* cache entry from the cache. We remember the least recently used entry by
* always pushing new entries and entries we look for onto the tail of a
* doubly linked list. This means that older items always bubble to the top
* of this LRU list.
*
* Sometimes our callers won't run their scans to completion. For example a
* semi-join only needs to run until it finds a matching tuple, and once it
* does, the join operator skips to the next outer tuple and does not execute
* the inner side again on that scan. Because of this, we must keep track of
* when a cache entry is complete, and by default, we know it is when we run
* out of tuples to read during the scan. However, there are cases where we
* can mark the cache entry as complete without exhausting the scan of all
* tuples. One case is unique joins, where the join operator knows that there
* will only be at most one match for any given outer tuple. In order to
* support such cases we allow the "singlerow" option to be set for the cache.
* This option marks the cache entry as complete after we read the first tuple
* from the subnode.
*
* It's possible when we're filling the cache for a given set of parameters
* that we're unable to free enough memory to store any more tuples. If this
* happens then we'll have already evicted all other cache entries. When
* caching another tuple would cause us to exceed our memory budget, we must
* free the entry that we're currently populating and move the state machine
* into MEMO_CACHE_BYPASS_MODE. This means that we'll not attempt to cache
* any further tuples for this particular scan. We don't have the memory for
* it. The state machine will be reset again on the next rescan. If the
* memory requirements to cache the next parameter's tuples are less
* demanding, then that may allow us to start putting useful entries back into
* the cache again.
*
*
* INTERFACE ROUTINES
* ExecMemoize - lookup cache, exec subplan when not found
* ExecInitMemoize - initialize node and subnodes
* ExecEndMemoize - shutdown node and subnodes
* ExecReScanMemoize - rescan the memoize node
*
* ExecMemoizeEstimate estimates DSM space needed for parallel plan
* ExecMemoizeInitializeDSM initialize DSM for parallel plan
* ExecMemoizeInitializeWorker attach to DSM info in parallel worker
* ExecMemoizeRetrieveInstrumentation get instrumentation from worker
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "common/hashfn.h"
#include "executor/executor.h"
#include "executor/nodeMemoize.h"
#include "lib/ilist.h"
#include "miscadmin.h"
#include "utils/datum.h"
#include "utils/lsyscache.h"
/* States of the ExecMemoize state machine */
#define MEMO_CACHE_LOOKUP 1 /* Attempt to perform a cache lookup */
#define MEMO_CACHE_FETCH_NEXT_TUPLE 2 /* Get another tuple from the cache */
#define MEMO_FILLING_CACHE 3 /* Read outer node to fill cache */
#define MEMO_CACHE_BYPASS_MODE 4 /* Bypass mode. Just read from our
* subplan without caching anything */
#define MEMO_END_OF_SCAN 5 /* Ready for rescan */
/* Helper macros for memory accounting */
#define EMPTY_ENTRY_MEMORY_BYTES(e) (sizeof(MemoizeEntry) + \
sizeof(MemoizeKey) + \
(e)->key->params->t_len);
#define CACHE_TUPLE_BYTES(t) (sizeof(MemoizeTuple) + \
(t)->mintuple->t_len)
/* MemoizeTuple Stores an individually cached tuple */
typedef struct MemoizeTuple
{
MinimalTuple mintuple; /* Cached tuple */
struct MemoizeTuple *next; /* The next tuple with the same parameter
* values or NULL if it's the last one */
} MemoizeTuple;
/*
* MemoizeKey
* The hash table key for cached entries plus the LRU list link
*/
typedef struct MemoizeKey
{
MinimalTuple params;
dlist_node lru_node; /* Pointer to next/prev key in LRU list */
} MemoizeKey;
/*
* MemoizeEntry
* The data struct that the cache hash table stores
*/
typedef struct MemoizeEntry
{
MemoizeKey *key; /* Hash key for hash table lookups */
MemoizeTuple *tuplehead; /* Pointer to the first tuple or NULL if no
* tuples are cached for this entry */
uint32 hash; /* Hash value (cached) */
char status; /* Hash status */
bool complete; /* Did we read the outer plan to completion? */
} MemoizeEntry;
#define SH_PREFIX memoize
#define SH_ELEMENT_TYPE MemoizeEntry
#define SH_KEY_TYPE MemoizeKey *
#define SH_SCOPE static inline
#define SH_DECLARE
#include "lib/simplehash.h"
static uint32 MemoizeHash_hash(struct memoize_hash *tb,
const MemoizeKey *key);
static bool MemoizeHash_equal(struct memoize_hash *tb,
const MemoizeKey *key1,
const MemoizeKey *key2);
#define SH_PREFIX memoize
#define SH_ELEMENT_TYPE MemoizeEntry
#define SH_KEY_TYPE MemoizeKey *
#define SH_KEY key
#define SH_HASH_KEY(tb, key) MemoizeHash_hash(tb, key)
#define SH_EQUAL(tb, a, b) MemoizeHash_equal(tb, a, b)
#define SH_SCOPE static inline
#define SH_STORE_HASH
#define SH_GET_HASH(tb, a) a->hash
#define SH_DEFINE
#include "lib/simplehash.h"
/*
* MemoizeHash_hash
* Hash function for simplehash hashtable. 'key' is unused here as we
* require that all table lookups first populate the MemoizeState's
* probeslot with the key values to be looked up.
*/
static uint32
MemoizeHash_hash(struct memoize_hash *tb, const MemoizeKey *key)
{
MemoizeState *mstate = (MemoizeState *) tb->private_data;
TupleTableSlot *pslot = mstate->probeslot;
uint32 hashkey = 0;
int numkeys = mstate->nkeys;
if (mstate->binary_mode)
{
for (int i = 0; i < numkeys; i++)
{
/* combine successive hashkeys by rotating */
hashkey = pg_rotate_left32(hashkey, 1);
if (!pslot->tts_isnull[i]) /* treat nulls as having hash key 0 */
{
FormData_pg_attribute *attr;
uint32 hkey;
attr = &pslot->tts_tupleDescriptor->attrs[i];
hkey = datum_image_hash(pslot->tts_values[i], attr->attbyval, attr->attlen);
hashkey ^= hkey;
}
}
}
else
{
FmgrInfo *hashfunctions = mstate->hashfunctions;
Oid *collations = mstate->collations;
for (int i = 0; i < numkeys; i++)
{
/* combine successive hashkeys by rotating */
hashkey = pg_rotate_left32(hashkey, 1);
if (!pslot->tts_isnull[i]) /* treat nulls as having hash key 0 */
{
uint32 hkey;
hkey = DatumGetUInt32(FunctionCall1Coll(&hashfunctions[i],
collations[i], pslot->tts_values[i]));
hashkey ^= hkey;
}
}
}
return murmurhash32(hashkey);
}
/*
* MemoizeHash_equal
* Equality function for confirming hash value matches during a hash
* table lookup. 'key2' is never used. Instead the MemoizeState's
* probeslot is always populated with details of what's being looked up.
*/
static bool
MemoizeHash_equal(struct memoize_hash *tb, const MemoizeKey *key1,
const MemoizeKey *key2)
{
MemoizeState *mstate = (MemoizeState *) tb->private_data;
ExprContext *econtext = mstate->ss.ps.ps_ExprContext;
TupleTableSlot *tslot = mstate->tableslot;
TupleTableSlot *pslot = mstate->probeslot;
/* probeslot should have already been prepared by prepare_probe_slot() */
ExecStoreMinimalTuple(key1->params, tslot, false);
if (mstate->binary_mode)
{
int numkeys = mstate->nkeys;
slot_getallattrs(tslot);
slot_getallattrs(pslot);
for (int i = 0; i < numkeys; i++)
{
FormData_pg_attribute *attr;
if (tslot->tts_isnull[i] != pslot->tts_isnull[i])
return false;
/* both NULL? they're equal */
if (tslot->tts_isnull[i])
continue;
/* perform binary comparison on the two datums */
attr = &tslot->tts_tupleDescriptor->attrs[i];
if (!datum_image_eq(tslot->tts_values[i], pslot->tts_values[i],
attr->attbyval, attr->attlen))
return false;
}
return true;
}
else
{
econtext->ecxt_innertuple = tslot;
econtext->ecxt_outertuple = pslot;
return ExecQualAndReset(mstate->cache_eq_expr, econtext);
}
}
/*
* Initialize the hash table to empty.
*/
static void
build_hash_table(MemoizeState *mstate, uint32 size)
{
/* Make a guess at a good size when we're not given a valid size. */
if (size == 0)
size = 1024;
/* memoize_create will convert the size to a power of 2 */
mstate->hashtable = memoize_create(mstate->tableContext, size, mstate);
}
/*
* prepare_probe_slot
* Populate mstate's probeslot with the values from the tuple stored
* in 'key'. If 'key' is NULL, then perform the population by evaluating
* mstate's param_exprs.
*/
static inline void
prepare_probe_slot(MemoizeState *mstate, MemoizeKey *key)
{
TupleTableSlot *pslot = mstate->probeslot;
TupleTableSlot *tslot = mstate->tableslot;
int numKeys = mstate->nkeys;
ExecClearTuple(pslot);
if (key == NULL)
{
ExprContext *econtext = mstate->ss.ps.ps_ExprContext;
MemoryContext oldcontext;
oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
/* Set the probeslot's values based on the current parameter values */
for (int i = 0; i < numKeys; i++)
pslot->tts_values[i] = ExecEvalExpr(mstate->param_exprs[i],
econtext,
&pslot->tts_isnull[i]);
MemoryContextSwitchTo(oldcontext);
}
else
{
/* Process the key's MinimalTuple and store the values in probeslot */
ExecStoreMinimalTuple(key->params, tslot, false);
slot_getallattrs(tslot);
memcpy(pslot->tts_values, tslot->tts_values, sizeof(Datum) * numKeys);
memcpy(pslot->tts_isnull, tslot->tts_isnull, sizeof(bool) * numKeys);
}
ExecStoreVirtualTuple(pslot);
}
/*
* entry_purge_tuples
* Remove all tuples from the cache entry pointed to by 'entry'. This
* leaves an empty cache entry. Also, update the memory accounting to
* reflect the removal of the tuples.
*/
static inline void
entry_purge_tuples(MemoizeState *mstate, MemoizeEntry *entry)
{
MemoizeTuple *tuple = entry->tuplehead;
uint64 freed_mem = 0;
while (tuple != NULL)
{
MemoizeTuple *next = tuple->next;
freed_mem += CACHE_TUPLE_BYTES(tuple);
/* Free memory used for this tuple */
pfree(tuple->mintuple);
pfree(tuple);
tuple = next;
}
entry->complete = false;
entry->tuplehead = NULL;
/* Update the memory accounting */
mstate->mem_used -= freed_mem;
}
/*
* remove_cache_entry
* Remove 'entry' from the cache and free memory used by it.
*/
static void
remove_cache_entry(MemoizeState *mstate, MemoizeEntry *entry)
{
MemoizeKey *key = entry->key;
dlist_delete(&entry->key->lru_node);
/* Remove all of the tuples from this entry */
entry_purge_tuples(mstate, entry);
/*
* Update memory accounting. entry_purge_tuples should have already
* subtracted the memory used for each cached tuple. Here we just update
* the amount used by the entry itself.
*/
mstate->mem_used -= EMPTY_ENTRY_MEMORY_BYTES(entry);
/* Remove the entry from the cache */
memoize_delete_item(mstate->hashtable, entry);
pfree(key->params);
pfree(key);
}
/*
* cache_purge_all
* Remove all items from the cache
*/
static void
cache_purge_all(MemoizeState *mstate)
{
uint64 evictions = mstate->hashtable->members;
PlanState *pstate = (PlanState *) mstate;
/*
* Likely the most efficient way to remove all items is to just reset the
* memory context for the cache and then rebuild a fresh hash table. This
* saves having to remove each item one by one and pfree each cached tuple
*/
MemoryContextReset(mstate->tableContext);
/* Make the hash table the same size as the original size */
build_hash_table(mstate, ((Memoize *) pstate->plan)->est_entries);
/* reset the LRU list */
dlist_init(&mstate->lru_list);
mstate->last_tuple = NULL;
mstate->entry = NULL;
mstate->mem_used = 0;
/* XXX should we add something new to track these purges? */
mstate->stats.cache_evictions += evictions; /* Update Stats */
}
/*
* cache_reduce_memory
* Evict older and less recently used items from the cache in order to
* reduce the memory consumption back to something below the
* MemoizeState's mem_limit.
*
* 'specialkey', if not NULL, causes the function to return false if the entry
* which the key belongs to is removed from the cache.
*/
static bool
cache_reduce_memory(MemoizeState *mstate, MemoizeKey *specialkey)
{
bool specialkey_intact = true; /* for now */
dlist_mutable_iter iter;
uint64 evictions = 0;
/* Update peak memory usage */
if (mstate->mem_used > mstate->stats.mem_peak)
mstate->stats.mem_peak = mstate->mem_used;
/* We expect only to be called when we've gone over budget on memory */
Assert(mstate->mem_used > mstate->mem_limit);
/* Start the eviction process starting at the head of the LRU list. */
dlist_foreach_modify(iter, &mstate->lru_list)
{
MemoizeKey *key = dlist_container(MemoizeKey, lru_node, iter.cur);
MemoizeEntry *entry;
/*
* Populate the hash probe slot in preparation for looking up this LRU
* entry.
*/
prepare_probe_slot(mstate, key);
/*
* Ideally the LRU list pointers would be stored in the entry itself
* rather than in the key. Unfortunately, we can't do that as the
* simplehash.h code may resize the table and allocate new memory for
* entries which would result in those pointers pointing to the old
* buckets. However, it's fine to use the key to store this as that's
* only referenced by a pointer in the entry, which of course follows
* the entry whenever the hash table is resized. Since we only have a
* pointer to the key here, we must perform a hash table lookup to
* find the entry that the key belongs to.
*/
entry = memoize_lookup(mstate->hashtable, NULL);
/*
* Sanity check that we found the entry belonging to the LRU list
* item. A misbehaving hash or equality function could cause the
* entry not to be found or the wrong entry to be found.
*/
if (unlikely(entry == NULL || entry->key != key))
elog(ERROR, "could not find memoization table entry");
/*
* If we're being called to free memory while the cache is being
* populated with new tuples, then we'd better take some care as we
* could end up freeing the entry which 'specialkey' belongs to.
* Generally callers will pass 'specialkey' as the key for the cache
* entry which is currently being populated, so we must set
* 'specialkey_intact' to false to inform the caller the specialkey
* entry has been removed.
*/
if (key == specialkey)
specialkey_intact = false;
/*
* Finally remove the entry. This will remove from the LRU list too.
*/
remove_cache_entry(mstate, entry);
evictions++;
/* Exit if we've freed enough memory */
if (mstate->mem_used <= mstate->mem_limit)
break;
}
mstate->stats.cache_evictions += evictions; /* Update Stats */
return specialkey_intact;
}
/*
* cache_lookup
* Perform a lookup to see if we've already cached tuples based on the
* scan's current parameters. If we find an existing entry we move it to
* the end of the LRU list, set *found to true then return it. If we
* don't find an entry then we create a new one and add it to the end of
* the LRU list. We also update cache memory accounting and remove older
* entries if we go over the memory budget. If we managed to free enough
* memory we return the new entry, else we return NULL.
*
* Callers can assume we'll never return NULL when *found is true.
*/
static MemoizeEntry *
cache_lookup(MemoizeState *mstate, bool *found)
{
MemoizeKey *key;
MemoizeEntry *entry;
MemoryContext oldcontext;
/* prepare the probe slot with the current scan parameters */
prepare_probe_slot(mstate, NULL);
/*
* Add the new entry to the cache. No need to pass a valid key since the
* hash function uses mstate's probeslot, which we populated above.
*/
entry = memoize_insert(mstate->hashtable, NULL, found);
if (*found)
{
/*
* Move existing entry to the tail of the LRU list to mark it as the
* most recently used item.
*/
dlist_move_tail(&mstate->lru_list, &entry->key->lru_node);
return entry;
}
oldcontext = MemoryContextSwitchTo(mstate->tableContext);
/* Allocate a new key */
entry->key = key = (MemoizeKey *) palloc(sizeof(MemoizeKey));
key->params = ExecCopySlotMinimalTuple(mstate->probeslot);
/* Update the total cache memory utilization */
mstate->mem_used += EMPTY_ENTRY_MEMORY_BYTES(entry);
/* Initialize this entry */
entry->complete = false;
entry->tuplehead = NULL;
/*
* Since this is the most recently used entry, push this entry onto the
* end of the LRU list.
*/
dlist_push_tail(&mstate->lru_list, &entry->key->lru_node);
mstate->last_tuple = NULL;
MemoryContextSwitchTo(oldcontext);
/*
* If we've gone over our memory budget, then we'll free up some space in
* the cache.
*/
if (mstate->mem_used > mstate->mem_limit)
{
/*
* Try to free up some memory. It's highly unlikely that we'll fail
* to do so here since the entry we've just added is yet to contain
* any tuples and we're able to remove any other entry to reduce the
* memory consumption.
*/
if (unlikely(!cache_reduce_memory(mstate, key)))
return NULL;
/*
* The process of removing entries from the cache may have caused the
* code in simplehash.h to shuffle elements to earlier buckets in the
* hash table. If it has, we'll need to find the entry again by
* performing a lookup. Fortunately, we can detect if this has
* happened by seeing if the entry is still in use and that the key
* pointer matches our expected key.
*/
if (entry->status != memoize_SH_IN_USE || entry->key != key)
{
/*
* We need to repopulate the probeslot as lookups performed during
* the cache evictions above will have stored some other key.
*/
prepare_probe_slot(mstate, key);
/* Re-find the newly added entry */
entry = memoize_lookup(mstate->hashtable, NULL);
Assert(entry != NULL);
}
}
return entry;
}
/*
* cache_store_tuple
* Add the tuple stored in 'slot' to the mstate's current cache entry.
* The cache entry must have already been made with cache_lookup().
* mstate's last_tuple field must point to the tail of mstate->entry's
* list of tuples.
*/
static bool
cache_store_tuple(MemoizeState *mstate, TupleTableSlot *slot)
{
MemoizeTuple *tuple;
MemoizeEntry *entry = mstate->entry;
MemoryContext oldcontext;
Assert(slot != NULL);
Assert(entry != NULL);
oldcontext = MemoryContextSwitchTo(mstate->tableContext);
tuple = (MemoizeTuple *) palloc(sizeof(MemoizeTuple));
tuple->mintuple = ExecCopySlotMinimalTuple(slot);
tuple->next = NULL;
/* Account for the memory we just consumed */
mstate->mem_used += CACHE_TUPLE_BYTES(tuple);
if (entry->tuplehead == NULL)
{
/*
* This is the first tuple for this entry, so just point the list head
* to it.
*/
entry->tuplehead = tuple;
}
else
{
/* push this tuple onto the tail of the list */
mstate->last_tuple->next = tuple;
}
mstate->last_tuple = tuple;
MemoryContextSwitchTo(oldcontext);
/*
* If we've gone over our memory budget then free up some space in the
* cache.
*/
if (mstate->mem_used > mstate->mem_limit)
{
MemoizeKey *key = entry->key;
if (!cache_reduce_memory(mstate, key))
return false;
/*
* The process of removing entries from the cache may have caused the
* code in simplehash.h to shuffle elements to earlier buckets in the
* hash table. If it has, we'll need to find the entry again by
* performing a lookup. Fortunately, we can detect if this has
* happened by seeing if the entry is still in use and that the key
* pointer matches our expected key.
*/
if (entry->status != memoize_SH_IN_USE || entry->key != key)
{
/*
* We need to repopulate the probeslot as lookups performed during
* the cache evictions above will have stored some other key.
*/
prepare_probe_slot(mstate, key);
/* Re-find the entry */
mstate->entry = entry = memoize_lookup(mstate->hashtable, NULL);
Assert(entry != NULL);
}
}
return true;
}
static TupleTableSlot *
ExecMemoize(PlanState *pstate)
{
MemoizeState *node = castNode(MemoizeState, pstate);
PlanState *outerNode;
TupleTableSlot *slot;
switch (node->mstatus)
{
case MEMO_CACHE_LOOKUP:
{
MemoizeEntry *entry;
TupleTableSlot *outerslot;
bool found;
Assert(node->entry == NULL);
/*
* We're only ever in this state for the first call of the
* scan. Here we have a look to see if we've already seen the
* current parameters before and if we have already cached a
* complete set of records that the outer plan will return for
* these parameters.
*
* When we find a valid cache entry, we'll return the first
* tuple from it. If not found, we'll create a cache entry and
* then try to fetch a tuple from the outer scan. If we find
* one there, we'll try to cache it.
*/
/* see if we've got anything cached for the current parameters */
entry = cache_lookup(node, &found);
if (found && entry->complete)
{
node->stats.cache_hits += 1; /* stats update */
/*
* Set last_tuple and entry so that the state
* MEMO_CACHE_FETCH_NEXT_TUPLE can easily find the next
* tuple for these parameters.
*/
node->last_tuple = entry->tuplehead;
node->entry = entry;
/* Fetch the first cached tuple, if there is one */
if (entry->tuplehead)
{
node->mstatus = MEMO_CACHE_FETCH_NEXT_TUPLE;
slot = node->ss.ps.ps_ResultTupleSlot;
ExecStoreMinimalTuple(entry->tuplehead->mintuple,
slot, false);
return slot;
}
/* The cache entry is void of any tuples. */
node->mstatus = MEMO_END_OF_SCAN;
return NULL;
}
/* Handle cache miss */
node->stats.cache_misses += 1; /* stats update */
if (found)
{
/*
* A cache entry was found, but the scan for that entry
* did not run to completion. We'll just remove all
* tuples and start again. It might be tempting to
* continue where we left off, but there's no guarantee
* the outer node will produce the tuples in the same
* order as it did last time.
*/
entry_purge_tuples(node, entry);
}
/* Scan the outer node for a tuple to cache */
outerNode = outerPlanState(node);
outerslot = ExecProcNode(outerNode);
if (TupIsNull(outerslot))
{
/*
* cache_lookup may have returned NULL due to failure to
* free enough cache space, so ensure we don't do anything
* here that assumes it worked. There's no need to go into
* bypass mode here as we're setting mstatus to end of
* scan.
*/
if (likely(entry))
entry->complete = true;
node->mstatus = MEMO_END_OF_SCAN;
return NULL;
}
node->entry = entry;
/*
* If we failed to create the entry or failed to store the
* tuple in the entry, then go into bypass mode.
*/
if (unlikely(entry == NULL ||
!cache_store_tuple(node, outerslot)))
{
node->stats.cache_overflows += 1; /* stats update */
node->mstatus = MEMO_CACHE_BYPASS_MODE;
/*
* No need to clear out last_tuple as we'll stay in bypass
* mode until the end of the scan.
*/
}
else
{
/*
* If we only expect a single row from this scan then we
* can mark that we're not expecting more. This allows
* cache lookups to work even when the scan has not been
* executed to completion.
*/
entry->complete = node->singlerow;
node->mstatus = MEMO_FILLING_CACHE;
}
slot = node->ss.ps.ps_ResultTupleSlot;
ExecCopySlot(slot, outerslot);
return slot;
}
case MEMO_CACHE_FETCH_NEXT_TUPLE:
{
/* We shouldn't be in this state if these are not set */
Assert(node->entry != NULL);
Assert(node->last_tuple != NULL);
/* Skip to the next tuple to output */
node->last_tuple = node->last_tuple->next;
/* No more tuples in the cache */
if (node->last_tuple == NULL)
{
node->mstatus = MEMO_END_OF_SCAN;
return NULL;
}
slot = node->ss.ps.ps_ResultTupleSlot;
ExecStoreMinimalTuple(node->last_tuple->mintuple, slot,
false);
return slot;
}
case MEMO_FILLING_CACHE:
{
TupleTableSlot *outerslot;
MemoizeEntry *entry = node->entry;
/* entry should already have been set by MEMO_CACHE_LOOKUP */
Assert(entry != NULL);
/*
* When in the MEMO_FILLING_CACHE state, we've just had a
* cache miss and are populating the cache with the current
* scan tuples.
*/
outerNode = outerPlanState(node);
outerslot = ExecProcNode(outerNode);
if (TupIsNull(outerslot))
{
/* No more tuples. Mark it as complete */
entry->complete = true;
node->mstatus = MEMO_END_OF_SCAN;
return NULL;
}
/*
* Validate if the planner properly set the singlerow flag. It
* should only set that if each cache entry can, at most,
* return 1 row.
*/
if (unlikely(entry->complete))
elog(ERROR, "cache entry already complete");
/* Record the tuple in the current cache entry */
if (unlikely(!cache_store_tuple(node, outerslot)))
{
/* Couldn't store it? Handle overflow */
node->stats.cache_overflows += 1; /* stats update */
node->mstatus = MEMO_CACHE_BYPASS_MODE;
/*
* No need to clear out entry or last_tuple as we'll stay
* in bypass mode until the end of the scan.
*/
}
slot = node->ss.ps.ps_ResultTupleSlot;
ExecCopySlot(slot, outerslot);
return slot;
}
case MEMO_CACHE_BYPASS_MODE:
{
TupleTableSlot *outerslot;
/*
* When in bypass mode we just continue to read tuples without
* caching. We need to wait until the next rescan before we
* can come out of this mode.
*/
outerNode = outerPlanState(node);
outerslot = ExecProcNode(outerNode);
if (TupIsNull(outerslot))
{
node->mstatus = MEMO_END_OF_SCAN;
return NULL;
}
slot = node->ss.ps.ps_ResultTupleSlot;
ExecCopySlot(slot, outerslot);
return slot;
}
case MEMO_END_OF_SCAN:
/*
* We've already returned NULL for this scan, but just in case
* something calls us again by mistake.
*/
return NULL;
default:
elog(ERROR, "unrecognized memoize state: %d",
(int) node->mstatus);
return NULL;
} /* switch */
}
MemoizeState *
ExecInitMemoize(Memoize *node, EState *estate, int eflags)
{
MemoizeState *mstate = makeNode(MemoizeState);
Plan *outerNode;
int i;
int nkeys;
Oid *eqfuncoids;
/* check for unsupported flags */
Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
mstate->ss.ps.plan = (Plan *) node;
mstate->ss.ps.state = estate;
mstate->ss.ps.ExecProcNode = ExecMemoize;
/*
* Miscellaneous initialization
*
* create expression context for node
*/
ExecAssignExprContext(estate, &mstate->ss.ps);
outerNode = outerPlan(node);
outerPlanState(mstate) = ExecInitNode(outerNode, estate, eflags);
/*
* Initialize return slot and type. No need to initialize projection info
* because this node doesn't do projections.
*/
ExecInitResultTupleSlotTL(&mstate->ss.ps, &TTSOpsMinimalTuple);
mstate->ss.ps.ps_ProjInfo = NULL;
/*
* Initialize scan slot and type.
*/
ExecCreateScanSlotFromOuterPlan(estate, &mstate->ss, &TTSOpsMinimalTuple);
/*
* Set the state machine to lookup the cache. We won't find anything
* until we cache something, but this saves a special case to create the
* first entry.
*/
mstate->mstatus = MEMO_CACHE_LOOKUP;
mstate->nkeys = nkeys = node->numKeys;
mstate->hashkeydesc = ExecTypeFromExprList(node->param_exprs);
mstate->tableslot = MakeSingleTupleTableSlot(mstate->hashkeydesc,
&TTSOpsMinimalTuple);
mstate->probeslot = MakeSingleTupleTableSlot(mstate->hashkeydesc,
&TTSOpsVirtual);
mstate->param_exprs = (ExprState **) palloc(nkeys * sizeof(ExprState *));
mstate->collations = node->collations; /* Just point directly to the plan
* data */
mstate->hashfunctions = (FmgrInfo *) palloc(nkeys * sizeof(FmgrInfo));
eqfuncoids = palloc(nkeys * sizeof(Oid));
for (i = 0; i < nkeys; i++)
{
Oid hashop = node->hashOperators[i];
Oid left_hashfn;
Oid right_hashfn;
Expr *param_expr = (Expr *) list_nth(node->param_exprs, i);
if (!get_op_hash_functions(hashop, &left_hashfn, &right_hashfn))
elog(ERROR, "could not find hash function for hash operator %u",
hashop);
fmgr_info(left_hashfn, &mstate->hashfunctions[i]);
mstate->param_exprs[i] = ExecInitExpr(param_expr, (PlanState *) mstate);
eqfuncoids[i] = get_opcode(hashop);
}
mstate->cache_eq_expr = ExecBuildParamSetEqual(mstate->hashkeydesc,
&TTSOpsMinimalTuple,
&TTSOpsVirtual,
eqfuncoids,
node->collations,
node->param_exprs,
(PlanState *) mstate);
pfree(eqfuncoids);
mstate->mem_used = 0;
/* Limit the total memory consumed by the cache to this */
mstate->mem_limit = get_hash_memory_limit();
/* A memory context dedicated for the cache */
mstate->tableContext = AllocSetContextCreate(CurrentMemoryContext,
"MemoizeHashTable",
ALLOCSET_DEFAULT_SIZES);
dlist_init(&mstate->lru_list);
mstate->last_tuple = NULL;
mstate->entry = NULL;
/*
* Mark if we can assume the cache entry is completed after we get the
* first record for it. Some callers might not call us again after
* getting the first match. e.g. A join operator performing a unique join
* is able to skip to the next outer tuple after getting the first
* matching inner tuple. In this case, the cache entry is complete after
* getting the first tuple. This allows us to mark it as so.
*/
mstate->singlerow = node->singlerow;
mstate->keyparamids = node->keyparamids;
/*
* Record if the cache keys should be compared bit by bit, or logically
* using the type's hash equality operator
*/
mstate->binary_mode = node->binary_mode;
/* Zero the statistics counters */
memset(&mstate->stats, 0, sizeof(MemoizeInstrumentation));
/* Allocate and set up the actual cache */
build_hash_table(mstate, node->est_entries);
return mstate;
}
void
ExecEndMemoize(MemoizeState *node)
{
#ifdef USE_ASSERT_CHECKING
/* Validate the memory accounting code is correct in assert builds. */
{
int count;
uint64 mem = 0;
memoize_iterator i;
MemoizeEntry *entry;
memoize_start_iterate(node->hashtable, &i);
count = 0;
while ((entry = memoize_iterate(node->hashtable, &i)) != NULL)
{
MemoizeTuple *tuple = entry->tuplehead;
mem += EMPTY_ENTRY_MEMORY_BYTES(entry);
while (tuple != NULL)
{
mem += CACHE_TUPLE_BYTES(tuple);
tuple = tuple->next;
}
count++;
}
Assert(count == node->hashtable->members);
Assert(mem == node->mem_used);
}
#endif
/*
* When ending a parallel worker, copy the statistics gathered by the
* worker back into shared memory so that it can be picked up by the main
* process to report in EXPLAIN ANALYZE.
*/
if (node->shared_info != NULL && IsParallelWorker())
{
MemoizeInstrumentation *si;
/* Make mem_peak available for EXPLAIN */
if (node->stats.mem_peak == 0)
node->stats.mem_peak = node->mem_used;
Assert(ParallelWorkerNumber <= node->shared_info->num_workers);
si = &node->shared_info->sinstrument[ParallelWorkerNumber];
memcpy(si, &node->stats, sizeof(MemoizeInstrumentation));
}
/* Remove the cache context */
MemoryContextDelete(node->tableContext);
ExecClearTuple(node->ss.ss_ScanTupleSlot);
/* must drop pointer to cache result tuple */
ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);
/*
* free exprcontext
*/
ExecFreeExprContext(&node->ss.ps);
/*
* shut down the subplan
*/
ExecEndNode(outerPlanState(node));
}
void
ExecReScanMemoize(MemoizeState *node)
{
PlanState *outerPlan = outerPlanState(node);
/* Mark that we must lookup the cache for a new set of parameters */
node->mstatus = MEMO_CACHE_LOOKUP;
/* nullify pointers used for the last scan */
node->entry = NULL;
node->last_tuple = NULL;
/*
* if chgParam of subnode is not null then plan will be re-scanned by
* first ExecProcNode.
*/
if (outerPlan->chgParam == NULL)
ExecReScan(outerPlan);
/*
* Purge the entire cache if a parameter changed that is not part of the
* cache key.
*/
if (bms_nonempty_difference(outerPlan->chgParam, node->keyparamids))
cache_purge_all(node);
}
/*
* ExecEstimateCacheEntryOverheadBytes
* For use in the query planner to help it estimate the amount of memory
* required to store a single entry in the cache.
*/
double
ExecEstimateCacheEntryOverheadBytes(double ntuples)
{
return sizeof(MemoizeEntry) + sizeof(MemoizeKey) + sizeof(MemoizeTuple) *
ntuples;
}
/* ----------------------------------------------------------------
* Parallel Query Support
* ----------------------------------------------------------------
*/
/* ----------------------------------------------------------------
* ExecMemoizeEstimate
*
* Estimate space required to propagate memoize statistics.
* ----------------------------------------------------------------
*/
void
ExecMemoizeEstimate(MemoizeState *node, ParallelContext *pcxt)
{
Size size;
/* don't need this if not instrumenting or no workers */
if (!node->ss.ps.instrument || pcxt->nworkers == 0)
return;
size = mul_size(pcxt->nworkers, sizeof(MemoizeInstrumentation));
size = add_size(size, offsetof(SharedMemoizeInfo, sinstrument));
shm_toc_estimate_chunk(&pcxt->estimator, size);
shm_toc_estimate_keys(&pcxt->estimator, 1);
}
/* ----------------------------------------------------------------
* ExecMemoizeInitializeDSM
*
* Initialize DSM space for memoize statistics.
* ----------------------------------------------------------------
*/
void
ExecMemoizeInitializeDSM(MemoizeState *node, ParallelContext *pcxt)
{
Size size;
/* don't need this if not instrumenting or no workers */
if (!node->ss.ps.instrument || pcxt->nworkers == 0)
return;
size = offsetof(SharedMemoizeInfo, sinstrument)
+ pcxt->nworkers * sizeof(MemoizeInstrumentation);
node->shared_info = shm_toc_allocate(pcxt->toc, size);
/* ensure any unfilled slots will contain zeroes */
memset(node->shared_info, 0, size);
node->shared_info->num_workers = pcxt->nworkers;
shm_toc_insert(pcxt->toc, node->ss.ps.plan->plan_node_id,
node->shared_info);
}
/* ----------------------------------------------------------------
* ExecMemoizeInitializeWorker
*
* Attach worker to DSM space for memoize statistics.
* ----------------------------------------------------------------
*/
void
ExecMemoizeInitializeWorker(MemoizeState *node, ParallelWorkerContext *pwcxt)
{
node->shared_info =
shm_toc_lookup(pwcxt->toc, node->ss.ps.plan->plan_node_id, true);
}
/* ----------------------------------------------------------------
* ExecMemoizeRetrieveInstrumentation
*
* Transfer memoize statistics from DSM to private memory.
* ----------------------------------------------------------------
*/
void
ExecMemoizeRetrieveInstrumentation(MemoizeState *node)
{
Size size;
SharedMemoizeInfo *si;
if (node->shared_info == NULL)
return;
size = offsetof(SharedMemoizeInfo, sinstrument)
+ node->shared_info->num_workers * sizeof(MemoizeInstrumentation);
si = palloc(size);
memcpy(si, node->shared_info, size);
node->shared_info = si;
}
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