rahulg wrote:
I am facing problem in tracing in what events the selectivity
histogram in pg_statistic is stored/updated.
I went through the code in src/backend/commands/analyze.c and got to
see the code computing the histogram but when I tried to trace the
caller of analyze_rel or compute_index_stats, I find out that only
during Vaccum command, these functions are invoked. I am little
surprised as I did get to see PostgreSQL giving good selectivity
estimations despite me running Vaccuum command even once.
I did try to trace the control flow during table operations
(creation / insertion) but couldn't find any histogram updation
functions being invoked though I did get to know that some functions
related to catalog updations is being invoked.
Can anybody tell me in what all events is the pg_statistic table
exactly updated?
The flow is like this:
analyze_rel() determines the type-specific analyze function to call for
each column:
http://git.postgresql.org/?p=postgresql.git;a=blob;f=src/backend/commands/analyze.c;h=d96b7666f08d9ac74cccf05851fa8fd8fc2d4948;hb=HEAD#l270
the function OID gets pulled from pg_type, from the typanalyze column:
http://www.postgresql.org/docs/8.3/static/catalog-pg-type.html
currently there is only one datatype that has a custom analyze function
(tsvector). All others get analyzed using the standard one:
http://git.postgresql.org/?p=postgresql.git;a=blob;f=src/backend/commands/analyze.c;h=d96b7666f08d9ac74cccf05851fa8fd8fc2d4948;hb=HEAD#l1489
depending on whether the datatype has a < operator or not, the column is
analyzed using compute_scalar_stats() or compute_minimal_stats().
The actual call of the chosen function happens here:
http://git.postgresql.org/?p=postgresql.git;a=blob;f=src/backend/commands/analyze.c;h=d96b7666f08d9ac74cccf05851fa8fd8fc2d4948;hb=HEAD#l425
And the write to pg_statistic happens here:
http://git.postgresql.org/?p=postgresql.git;a=blob;f=src/backend/commands/analyze.c;h=d96b7666f08d9ac74cccf05851fa8fd8fc2d4948;hb=HEAD#l446
HTH,
Jan
--
Jan Urbanski
GPG key ID: E583D7D2
ouden estin
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
