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You In Here : //proc/self/root/usr/include/pgsql/ 1 then tuples that don't belong in first batch get saved * into inner-batch temp files. The same statements apply for the * first scan of the outer relation, except we write tuples to outer-batch * temp files. After finishing the first scan, we do the following for * each remaining batch: * 1. Read tuples from inner batch file, load into hash buckets. * 2. Read tuples from outer batch file, match to hash buckets and output. * * It is possible to increase nbatch on the fly if the in-memory hash table * gets too big. The hash-value-to-batch computation is arranged so that this * can only cause a tuple to go into a later batch than previously thought, * never into an earlier batch. When we increase nbatch, we rescan the hash * table and dump out any tuples that are now of a later batch to the correct * inner batch file. Subsequently, while reading either inner or outer batch * files, we might find tuples that no longer belong to the current batch; * if so, we just dump them out to the correct batch file. * ---------------------------------------------------------------- */ /* these are in nodes/execnodes.h: */ /* typedef struct HashJoinTupleData *HashJoinTuple; */ /* typedef struct HashJoinTableData *HashJoinTable; */ typedef struct HashJoinTupleData { struct HashJoinTupleData *next; /* link to next tuple in same bucket */ uint32 hashvalue; /* tuple's hash code */ /* Tuple data, in MinimalTuple format, follows on a MAXALIGN boundary */ } HashJoinTupleData; #define HJTUPLE_OVERHEAD MAXALIGN(sizeof(HashJoinTupleData)) #define HJTUPLE_MINTUPLE(hjtup) \ ((MinimalTuple) ((char *) (hjtup) + HJTUPLE_OVERHEAD)) /* * If the outer relation's distribution is sufficiently nonuniform, we attempt * to optimize the join by treating the hash values corresponding to the outer * relation's MCVs specially. Inner relation tuples matching these hash * values go into the "skew" hashtable instead of the main hashtable, and * outer relation tuples with these hash values are matched against that * table instead of the main one. Thus, tuples with these hash values are * effectively handled as part of the first batch and will never go to disk. * The skew hashtable is limited to SKEW_WORK_MEM_PERCENT of the total memory * allowed for the join; while building the hashtables, we decrease the number * of MCVs being specially treated if needed to stay under this limit. * * Note: you might wonder why we look at the outer relation stats for this, * rather than the inner. One reason is that the outer relation is typically * bigger, so we get more I/O savings by optimizing for its most common values. * Also, for similarly-sized relations, the planner prefers to put the more * uniformly distributed relation on the inside, so we're more likely to find * interesting skew in the outer relation. */ typedef struct HashSkewBucket { uint32 hashvalue; /* common hash value */ HashJoinTuple tuples; /* linked list of inner-relation tuples */ } HashSkewBucket; #define SKEW_BUCKET_OVERHEAD MAXALIGN(sizeof(HashSkewBucket)) #define INVALID_SKEW_BUCKET_NO (-1) #define SKEW_WORK_MEM_PERCENT 2 #define SKEW_MIN_OUTER_FRACTION 0.01 typedef struct HashJoinTableData { int nbuckets; /* # buckets in the in-memory hash table */ int log2_nbuckets; /* its log2 (nbuckets must be a power of 2) */ /* buckets[i] is head of list of tuples in i'th in-memory bucket */ struct HashJoinTupleData **buckets; /* buckets array is per-batch storage, as are all the tuples */ bool keepNulls; /* true to store unmatchable NULL tuples */ bool skewEnabled; /* are we using skew optimization? */ HashSkewBucket **skewBucket; /* hashtable of skew buckets */ int skewBucketLen; /* size of skewBucket array (a power of 2!) */ int nSkewBuckets; /* number of active skew buckets */ int *skewBucketNums; /* array indexes of active skew buckets */ int nbatch; /* number of batches */ int curbatch; /* current batch #; 0 during 1st pass */ int nbatch_original; /* nbatch when we started inner scan */ int nbatch_outstart; /* nbatch when we started outer scan */ bool growEnabled; /* flag to shut off nbatch increases */ double totalTuples; /* # tuples obtained from inner plan */ /* * These arrays are allocated for the life of the hash join, but only if * nbatch > 1. A file is opened only when we first write a tuple into it * (otherwise its pointer remains NULL). Note that the zero'th array * elements never get used, since we will process rather than dump out any * tuples of batch zero. */ BufFile **innerBatchFile; /* buffered virtual temp file per batch */ BufFile **outerBatchFile; /* buffered virtual temp file per batch */ /* * Info about the datatype-specific hash functions for the datatypes being * hashed. These are arrays of the same length as the number of hash join * clauses (hash keys). */ FmgrInfo *outer_hashfunctions; /* lookup data for hash functions */ FmgrInfo *inner_hashfunctions; /* lookup data for hash functions */ bool *hashStrict; /* is each hash join operator strict? */ Size spaceUsed; /* memory space currently used by tuples */ Size spaceAllowed; /* upper limit for space used */ Size spacePeak; /* peak space used */ Size spaceUsedSkew; /* skew hash table's current space usage */ Size spaceAllowedSkew; /* upper limit for skew hashtable */ MemoryContext hashCxt; /* context for whole-hash-join storage */ MemoryContext batchCxt; /* context for this-batch-only storage */ } HashJoinTableData; #endif /* HASHJOIN_H */