pgpa_output.h File Reference

#include "pgpa_identifier.h"
#include "pgpa_walker.h"

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Functions
void	pgpa_output_advice (StringInfo buf, pgpa_plan_walker_context *walker, pgpa_identifier *rt_identifiers)

Function Documentation

pgpa_output_advice()

void pgpa_output_advice ( StringInfo  buf, pgpa_plan_walker_context *  walker, pgpa_identifier *  rt_identifiers  )

extern

Definition at line 78 of file pgpa_output.c.

{
    Index       rtable_length = list_length(walker->pstmt->rtable);
    ListCell   *lc;
    pgpa_output_context context;
 
    /* Basic initialization. */
    memset(&context, 0, sizeof(pgpa_output_context));
    context.buf = buf;
 
    /*
     * Convert identifiers to string form. Note that the loop variable here is
     * not an RTI, because RTIs are 1-based. Some RTIs will have no
     * identifier, either because the reloptkind is RTE_JOIN or because that
     * portion of the query didn't make it into the final plan.
     */
    context.rid_strings = palloc0_array(const char *, rtable_length);
    for (int i = 0; i < rtable_length; ++i)
        if (rt_identifiers[i].alias_name != NULL)
            context.rid_strings[i] = pgpa_identifier_string(&rt_identifiers[i]);
 
    /*
     * If the user chooses to use EXPLAIN (PLAN_ADVICE) in an 80-column window
     * from a psql client with default settings, psql will add one space to
     * the left of the output and EXPLAIN will add two more to the left of the
     * advice. Thus, lines of more than 77 characters will wrap. We set the
     * wrap limit to 76 here so that the output won't reach all the way to the
     * very last column of the terminal.
     *
     * Of course, this is fairly arbitrary set of assumptions, and one could
     * well make an argument for a different wrap limit, or for a configurable
     * one.
     */
    context.wrap_column = 76;
 
    /*
     * Each piece of JOIN_ORDER() advice fully describes the join order for a
     * a single unrolled join. Merging is not permitted, because that would
     * change the meaning, e.g. SEQ_SCAN(a b c d) means simply that sequential
     * scans should be used for all of those relations, and is thus equivalent
     * to SEQ_SCAN(a b) SEQ_SCAN(c d), but JOIN_ORDER(a b c d) means that "a"
     * is the driving table which is then joined to "b" then "c" then "d",
     * which is totally different from JOIN_ORDER(a b) and JOIN_ORDER(c d).
     */
    foreach(lc, walker->toplevel_unrolled_joins)
    {
        pgpa_unrolled_join *ujoin = lfirst(lc);
 
        if (buf->len > 0)
            appendStringInfoChar(buf, '\n');
        appendStringInfo(context.buf, "JOIN_ORDER(");
        pgpa_output_unrolled_join(&context, ujoin);
        appendStringInfoChar(context.buf, ')');
        pgpa_maybe_linebreak(context.buf, context.wrap_column);
    }
 
    /* Emit join strategy advice. */
    for (int s = 0; s < NUM_PGPA_JOIN_STRATEGY; ++s)
    {
        char       *strategy = pgpa_cstring_join_strategy(s);
 
        pgpa_output_simple_strategy(&context,
                                    strategy,
                                    walker->join_strategies[s]);
    }
 
    /*
     * Emit scan strategy advice (but not for ordinary scans, which are
     * definitionally uninteresting).
     */
    for (int c = 0; c < NUM_PGPA_SCAN_STRATEGY; ++c)
        if (c != PGPA_SCAN_ORDINARY)
            pgpa_output_scan_strategy(&context, c, walker->scans[c]);
 
    /* Emit query feature advice. */
    for (int t = 0; t < NUM_PGPA_QF_TYPES; ++t)
        pgpa_output_query_feature(&context, t, walker->query_features[t]);
 
    /* Emit NO_GATHER advice. */
    pgpa_output_no_gather(&context, walker->no_gather_scans);
}

References appendStringInfo(), appendStringInfoChar(), pgpa_output_context::buf, buf, fb(), i, lfirst, list_length(), NUM_PGPA_JOIN_STRATEGY, NUM_PGPA_QF_TYPES, NUM_PGPA_SCAN_STRATEGY, palloc0_array, pgpa_cstring_join_strategy(), pgpa_identifier_string(), pgpa_maybe_linebreak(), pgpa_output_no_gather(), pgpa_output_query_feature(), pgpa_output_scan_strategy(), pgpa_output_simple_strategy(), pgpa_output_unrolled_join(), PGPA_SCAN_ORDINARY, pgpa_output_context::rid_strings, and pgpa_output_context::wrap_column.

Referenced by pgpa_planner_shutdown().