/src/postgres/src/backend/executor/nodeMemoize.c

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/*-------------------------------------------------------------------------
 *
 * nodeMemoize.c
 *    Routines to handle caching of results from parameterized nodes
 *
 * Portions Copyright (c) 2021-2025, 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 inner
 * 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;
  ExprContext *econtext = mstate->ss.ps.ps_ExprContext;
  MemoryContext oldcontext;
  TupleTableSlot *pslot = mstate->probeslot;
  uint32    hashkey = 0;
  int     numkeys = mstate->nkeys;

  oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);

  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 */
      {
        CompactAttribute *attr;
        uint32    hkey;

        attr = TupleDescCompactAttr(pslot->tts_tupleDescriptor, 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;
      }
    }
  }

  MemoryContextSwitchTo(oldcontext);
  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)
  {
    MemoryContext oldcontext;
    int     numkeys = mstate->nkeys;
    bool    match = true;

    oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);

    slot_getallattrs(tslot);
    slot_getallattrs(pslot);

    for (int i = 0; i < numkeys; i++)
    {
      CompactAttribute *attr;

      if (tslot->tts_isnull[i] != pslot->tts_isnull[i])
      {
        match = false;
        break;
      }

      /* both NULL? they're equal */
      if (tslot->tts_isnull[i])
        continue;

      /* perform binary comparison on the two datums */
      attr = TupleDescCompactAttr(tslot->tts_tupleDescriptor, i);
      if (!datum_image_eq(tslot->tts_values[i], pslot->tts_values[i],
                attr->attbyval, attr->attlen))
      {
        match = false;
        break;
      }
    }

    MemoryContextSwitchTo(oldcontext);
    return match;
  }
  else
  {
    econtext->ecxt_innertuple = tslot;
    econtext->ecxt_outertuple = pslot;
    return ExecQual(mstate->cache_eq_expr, econtext);
  }
}

/*
 * Initialize the hash table to empty.  The MemoizeState's hashtable field
 * must point to NULL.
 */
static void
build_hash_table(MemoizeState *mstate, uint32 size)
{
  Assert(mstate->hashtable == NULL);

  /* 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 = 0;

  if (mstate->hashtable != NULL)
    evictions = mstate->hashtable->members;

  /*
   * 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);

  /* NULLify so we recreate the table on the next call */
  mstate->hashtable = NULL;

  /* 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);
  ExprContext *econtext = node->ss.ps.ps_ExprContext;
  PlanState  *outerNode;
  TupleTableSlot *slot;

  CHECK_FOR_INTERRUPTS();

  /*
   * Reset per-tuple memory context to free any expression evaluation
   * storage allocated in the previous tuple cycle.
   */
  ResetExprContext(econtext);

  switch (node->mstatus)
  {
    case MEMO_CACHE_LOOKUP:
      {
        MemoizeEntry *entry;
        TupleTableSlot *outerslot;
        bool    found;

        Assert(node->entry == NULL);

        /* first call? we'll need a hash table. */
        if (unlikely(node->hashtable == NULL))
          build_hash_table(node, ((Memoize *) pstate->plan)->est_entries);

        /*
         * 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));

  /*
   * Because it may require a large allocation, we delay building of the
   * hash table until executor run.
   */
  mstate->hashtable = NULL;

  return mstate;
}

void
ExecEndMemoize(MemoizeState *node)
{
#ifdef USE_ASSERT_CHECKING
  /* Validate the memory accounting code is correct in assert builds. */
  if (node->hashtable != NULL)
  {
    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);

  /*
   * 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;
}

Coverage Report

Created: 2025-07-03 06:49