Subquery optimization backport:

- Factor out subquery code into sql/opt_subselect.{h,cc}
- Stop using the term "confluent" (was used due to misreading the dictionary)

1 files changed, 368 insertions, 0 deletions

diff --git a/sql/opt_subselect.h b/sql/opt_subselect.h
new file mode 100644
index 00000000000..d8716dbb77f
--- /dev/null
+++ b/sql/opt_subselect.h
@@ -0,0 +1,368 @@
+/* */
+
+#ifdef USE_PRAGMA_INTERFACE
+#pragma interface			/* gcc class implementation */
+#endif
+
+int check_and_do_in_subquery_rewrites(JOIN *join);
+bool convert_join_subqueries_to_semijoins(JOIN *join);
+int pull_out_semijoin_tables(JOIN *join);
+bool optimize_semijoin_nests(JOIN *join, table_map all_table_map);
+
+// used by Loose_scan_opt
+ulonglong get_bound_sj_equalities(TABLE_LIST *sj_nest, 
+                                  table_map remaining_tables);
+
+/*
+  This is a class for considering possible loose index scan optimizations.
+  It's usage pattern is as follows:
+    best_access_path()
+    {
+       Loose_scan_opt opt;
+
+       opt.init()
+       for each index we can do ref access with
+       {
+         opt.next_ref_key();
+         for each keyuse 
+           opt.add_keyuse();
+         opt.check_ref_access();
+       }
+
+       if (some criteria for range scans)
+         opt.check_range_access();
+       
+       opt.get_best_option();
+    }
+*/
+
+class Loose_scan_opt
+{
+public:
+  /* All methods must check this before doing anything else */
+  bool try_loosescan;
+
+  /*
+    If we consider (oe1, .. oeN) IN (SELECT ie1, .. ieN) then ieK=oeK is
+    called sj-equality. If oeK depends only on preceding tables then such
+    equality is called 'bound'.
+  */
+  ulonglong bound_sj_equalities;
+ 
+  /* Accumulated properties of ref access we're now considering: */
+  ulonglong handled_sj_equalities;
+  key_part_map loose_scan_keyparts;
+  uint max_loose_keypart;
+  bool part1_conds_met;
+
+  /*
+    Use of quick select is a special case. Some of its properties:
+  */
+  uint quick_uses_applicable_index;
+  uint quick_max_loose_keypart;
+  
+  /* Best loose scan method so far */
+  uint   best_loose_scan_key;
+  double best_loose_scan_cost;
+  double best_loose_scan_records;
+  KEYUSE *best_loose_scan_start_key;
+
+  uint best_max_loose_keypart;
+
+  Loose_scan_opt():
+    try_loosescan(FALSE),
+    bound_sj_equalities(0),
+    quick_uses_applicable_index(FALSE)
+  {
+    UNINIT_VAR(quick_max_loose_keypart); /* Protected by quick_uses_applicable_index */
+    /* The following are protected by best_loose_scan_cost!= DBL_MAX */
+    UNINIT_VAR(best_loose_scan_key);
+    UNINIT_VAR(best_loose_scan_records);
+    UNINIT_VAR(best_max_loose_keypart);
+    UNINIT_VAR(best_loose_scan_start_key);
+  }
+  
+  void init(JOIN *join, JOIN_TAB *s, table_map remaining_tables)
+  {
+    /*
+      Discover the bound equalities. We need to do this if
+        1. The next table is an SJ-inner table, and
+        2. It is the first table from that semijoin, and
+        3. We're not within a semi-join range (i.e. all semi-joins either have
+           all or none of their tables in join_table_map), except
+           s->emb_sj_nest (which we've just entered, see #2).
+        4. All non-IN-equality correlation references from this sj-nest are 
+           bound
+        5. But some of the IN-equalities aren't (so this can't be handled by 
+           FirstMatch strategy)
+    */
+    best_loose_scan_cost= DBL_MAX;
+    if (!join->emb_sjm_nest && s->emb_sj_nest &&                        // (1)
+        s->emb_sj_nest->sj_in_exprs < 64 && 
+        ((remaining_tables & s->emb_sj_nest->sj_inner_tables) ==        // (2)
+         s->emb_sj_nest->sj_inner_tables) &&                            // (2)
+        join->cur_sj_inner_tables == 0 &&                                  // (3)
+        !(remaining_tables & 
+          s->emb_sj_nest->nested_join->sj_corr_tables) &&               // (4)
+        remaining_tables & s->emb_sj_nest->nested_join->sj_depends_on &&// (5)
+        optimizer_flag(join->thd, OPTIMIZER_SWITCH_LOOSE_SCAN))
+    {
+      /* This table is an LooseScan scan candidate */
+      bound_sj_equalities= get_bound_sj_equalities(s->emb_sj_nest, 
+                                                   remaining_tables);
+      try_loosescan= TRUE;
+      DBUG_PRINT("info", ("Will try LooseScan scan, bound_map=%llx",
+                          (longlong)bound_sj_equalities));
+    }
+  }
+
+  void next_ref_key()
+  {
+    handled_sj_equalities=0;
+    loose_scan_keyparts= 0;
+    max_loose_keypart= 0;
+    part1_conds_met= FALSE;
+  }
+  
+  void add_keyuse(table_map remaining_tables, KEYUSE *keyuse)
+  {
+    if (try_loosescan && keyuse->sj_pred_no != UINT_MAX)
+    {
+      if (!(remaining_tables & keyuse->used_tables))
+      {
+        /* 
+          This allows to use equality propagation to infer that some 
+          sj-equalities are bound.
+        */
+        bound_sj_equalities |= 1ULL << keyuse->sj_pred_no;
+      }
+      else
+      {
+        handled_sj_equalities |= 1ULL << keyuse->sj_pred_no;
+        loose_scan_keyparts |= ((key_part_map)1) << keyuse->keypart;
+        set_if_bigger(max_loose_keypart, keyuse->keypart);
+      }
+    }
+  }
+
+  bool have_a_case() { return test(handled_sj_equalities); }
+
+  void check_ref_access_part1(JOIN_TAB *s, uint key, KEYUSE *start_key, 
+                              table_map found_part)
+  {
+    /*
+      Check if we can use LooseScan semi-join strategy. We can if
+      1. This is the right table at right location
+      2. All IN-equalities are either
+         - "bound", ie. the outer_expr part refers to the preceding tables
+         - "handled", ie. covered by the index we're considering
+      3. Index order allows to enumerate subquery's duplicate groups in
+         order. This happens when the index definition matches this
+         pattern:
+
+           (handled_col|bound_col)* (other_col|bound_col)
+
+    */
+    if (try_loosescan &&                                       // (1)
+        (handled_sj_equalities | bound_sj_equalities) ==         // (2)
+        PREV_BITS(ulonglong, s->emb_sj_nest->sj_in_exprs) &&     // (2)
+        (PREV_BITS(key_part_map, max_loose_keypart+1) &        // (3)
+         (found_part | loose_scan_keyparts)) ==                // (3)
+         (found_part | loose_scan_keyparts) &&                 // (3)
+        !key_uses_partial_cols(s->table, key))
+    {
+      /* Ok, can use the strategy */
+      part1_conds_met= TRUE;
+      if (s->quick && s->quick->index == key && 
+          s->quick->get_type() == QUICK_SELECT_I::QS_TYPE_RANGE)
+      {
+        quick_uses_applicable_index= TRUE;
+        quick_max_loose_keypart= max_loose_keypart;
+      }
+      DBUG_PRINT("info", ("Can use LooseScan scan"));
+
+      /* 
+        Check if this is a special case where there are no usable bound
+        IN-equalities, i.e. we have
+
+          outer_expr IN (SELECT innertbl.key FROM ...) 
+        
+        and outer_expr cannot be evaluated yet, so it's actually full
+        index scan and not a ref access
+      */
+      if (!(found_part & 1 ) && /* no usable ref access for 1st key part */
+          s->table->covering_keys.is_set(key))
+      {
+        DBUG_PRINT("info", ("Can use full index scan for LooseScan"));
+        
+        /* Calculate the cost of complete loose index scan.  */
+        double records= rows2double(s->table->file->stats.records);
+
+        /* The cost is entire index scan cost (divided by 2) */
+        double read_time= s->table->file->index_only_read_time(key, records);
+
+        /*
+          Now find out how many different keys we will get (for now we
+          ignore the fact that we have "keypart_i=const" restriction for
+          some key components, that may make us think think that loose
+          scan will produce more distinct records than it actually will)
+        */
+        ulong rpc;
+        if ((rpc= s->table->key_info[key].rec_per_key[max_loose_keypart]))
+          records= records / rpc;
+
+        // TODO: previous version also did /2
+        if (read_time < best_loose_scan_cost)
+        {
+          best_loose_scan_key= key;
+          best_loose_scan_cost= read_time;
+          best_loose_scan_records= records;
+          best_max_loose_keypart= max_loose_keypart;
+          best_loose_scan_start_key= start_key;
+        }
+      }
+    }
+  }
+  
+  void check_ref_access_part2(uint key, KEYUSE *start_key, double records, 
+                              double read_time)
+  {
+    if (part1_conds_met && read_time < best_loose_scan_cost)
+    {
+      /* TODO use rec-per-key-based fanout calculations */
+      best_loose_scan_key= key;
+      best_loose_scan_cost= read_time;
+      best_loose_scan_records= records;
+      best_max_loose_keypart= max_loose_keypart;
+      best_loose_scan_start_key= start_key;
+    }
+  }
+
+  void check_range_access(JOIN *join, uint idx, QUICK_SELECT_I *quick)
+  {
+    /* TODO: this the right part restriction: */
+    if (quick_uses_applicable_index && idx == join->const_tables && 
+        quick->read_time < best_loose_scan_cost)
+    {
+      best_loose_scan_key= quick->index;
+      best_loose_scan_cost= quick->read_time;
+      /* this is ok because idx == join->const_tables */
+      best_loose_scan_records= rows2double(quick->records);
+      best_max_loose_keypart= quick_max_loose_keypart;
+      best_loose_scan_start_key= NULL;
+    }
+  }
+
+  void save_to_position(JOIN_TAB *tab, POSITION *pos)
+  {
+    pos->read_time=       best_loose_scan_cost;
+    if (best_loose_scan_cost != DBL_MAX)
+    {
+      pos->records_read=    best_loose_scan_records;
+      pos->key=             best_loose_scan_start_key;
+      pos->loosescan_key=   best_loose_scan_key;
+      pos->loosescan_parts= best_max_loose_keypart + 1;
+      pos->use_join_buffer= FALSE;
+      pos->table=           tab;
+      // todo need ref_depend_map ?
+      DBUG_PRINT("info", ("Produced a LooseScan plan, key %s, %s",
+                          tab->table->key_info[best_loose_scan_key].name,
+                          best_loose_scan_start_key? "(ref access)":
+                                                     "(range/index access)"));
+    }
+  }
+};
+
+
+void advance_sj_state(JOIN *join, const table_map remaining_tables, 
+                      const JOIN_TAB *new_join_tab, uint idx, 
+                      double *current_record_count, double *current_read_time,
+                      POSITION *loose_scan_pos);
+void restore_prev_sj_state(const table_map remaining_tables, 
+                                  const JOIN_TAB *tab, uint idx);
+
+void fix_semijoin_strategies_for_picked_join_order(JOIN *join);
+bool setup_sj_materialization(JOIN_TAB *tab);
+
+TABLE *create_duplicate_weedout_tmp_table(THD *thd, uint uniq_tuple_length_arg,
+                                          SJ_TMP_TABLE *sjtbl);
+int do_sj_reset(SJ_TMP_TABLE *sj_tbl);
+int do_sj_dups_weedout(THD *thd, SJ_TMP_TABLE *sjtbl);
+
+/*
+  Temporary table used by semi-join DuplicateElimination strategy
+
+  This consists of the temptable itself and data needed to put records
+  into it. The table's DDL is as follows:
+
+    CREATE TABLE tmptable (col VARCHAR(n) BINARY, PRIMARY KEY(col));
+
+  where the primary key can be replaced with unique constraint if n exceeds
+  the limit (as it is always done for query execution-time temptables).
+
+  The record value is a concatenation of rowids of tables from the join we're
+  executing. If a join table is on the inner side of the outer join, we
+  assume that its rowid can be NULL and provide means to store this rowid in
+  the tuple.
+*/
+
+class SJ_TMP_TABLE : public Sql_alloc
+{
+public:
+  /*
+    Array of pointers to tables whose rowids compose the temporary table
+    record.
+  */
+  class TAB
+  {
+  public:
+    JOIN_TAB *join_tab;
+    uint rowid_offset;
+    ushort null_byte;
+    uchar null_bit;
+  };
+  TAB *tabs;
+  TAB *tabs_end;
+  
+  /* 
+    is_degenerate==TRUE means this is a special case where the temptable record
+    has zero length (and presence of a unique key means that the temptable can
+    have either 0 or 1 records). 
+    In this case we don't create the physical temptable but instead record
+    its state in SJ_TMP_TABLE::have_degenerate_row.
+  */
+  bool is_degenerate;
+
+  /* 
+    When is_degenerate==TRUE: the contents of the table (whether it has the
+    record or not).
+  */
+  bool have_degenerate_row;
+  
+  /* table record parameters */
+  uint null_bits;
+  uint null_bytes;
+  uint rowid_len;
+
+  /* The temporary table itself (NULL means not created yet) */
+  TABLE *tmp_table;
+  
+  /*
+    These are the members we got from temptable creation code. We'll need
+    them if we'll need to convert table from HEAP to MyISAM/Maria.
+  */
+  ENGINE_COLUMNDEF *start_recinfo;
+  ENGINE_COLUMNDEF *recinfo;
+
+  /* Pointer to next table (next->start_idx > this->end_idx) */
+  SJ_TMP_TABLE *next; 
+};
+
+int setup_semijoin_dups_elimination(JOIN *join, ulonglong options, 
+                                    uint no_jbuf_after);
+void destroy_sj_tmp_tables(JOIN *join);
+int clear_sj_tmp_tables(JOIN *join);
+int rewrite_to_index_subquery_engine(JOIN *join);
+
+
+