- setting of -1 selects a size equal to four times the size of
- linkend="guc-shared-buffers">, but not less than the size of one
- shared buffer page, typically 8kB. This value
- can be set manually if the automatic choice is too large or too
- small.
-
-
- This value is factored into estimates of the cost of using an index;
- a higher value makes it more likely index scans will be used, a
+ disk cache that is available to a single query. This is
+ factored into estimates of the cost of using an index; a
+ higher value makes it more likely index scans will be used, a
lower value makes it more likely sequential scans will be
used. When setting this parameter you should consider both
PostgreSQL's shared buffers and the
memory allocated by
PostgreSQL, nor
does it reserve kernel disk cache; it is used only for estimation
purposes. The system also does not assume data remains in
- the disk cache between queries. The auto-tuning
- selected by the default setting of -1 should give reasonable
- results if this database cluster can utilize most of the memory
- on this server.
+ the disk cache between queries.
+
+
+ If effective_cache_size is set to -1, which is the
+ default, the value is replaced by an automatically selected value,
+ currently four times the size of .
+ For recommended settings of shared_buffers, this should
+ give reasonable results if this database cluster can use most of the
+ memory on the server.
#ifdef _MSC_VER
#include /* for _isnan */
#endif
+#include
#include
#include "access/htup_details.h"
#define LOG2(x) (log(x) / 0.693147180559945)
+
double seq_page_cost = DEFAULT_SEQ_PAGE_COST;
double random_page_cost = DEFAULT_RANDOM_PAGE_COST;
double cpu_tuple_cost = DEFAULT_CPU_TUPLE_COST;
double cpu_index_tuple_cost = DEFAULT_CPU_INDEX_TUPLE_COST;
double cpu_operator_cost = DEFAULT_CPU_OPERATOR_COST;
-int effective_cache_size = -1;
+int effective_cache_size = -1; /* will get replaced */
Cost disable_cost = 1.0e10;
path->path.total_cost = startup_cost + run_cost;
}
-void
-set_default_effective_cache_size(void)
-{
- /*
- * If the value of effective_cache_size is -1, use the preferred
- * auto-tune value.
- */
- if (effective_cache_size == -1)
- {
- char buf[32];
-
- snprintf(buf, sizeof(buf), "%d", NBuffers * DEFAULT_EFFECTIVE_CACHE_SIZE_MULTI);
- SetConfigOption("effective_cache_size", buf, PGC_POSTMASTER, PGC_S_OVERRIDE);
- }
- Assert(effective_cache_size > 0);
-}
-
-/*
- * GUC check_hook for effective_cache_size
- */
-bool
-check_effective_cache_size(int *newval, void **extra, GucSource source)
-{
- /*
- * -1 indicates a request for auto-tune.
- */
- if (*newval == -1)
- {
- /*
- * If we haven't yet changed the boot_val default of -1, just let it
- * be. We'll fix it later.
- */
- if (effective_cache_size == -1)
- return true;
-
- /* Otherwise, substitute the auto-tune value */
- *newval = NBuffers * DEFAULT_EFFECTIVE_CACHE_SIZE_MULTI;
- }
-
- /* set minimum? */
- if (*newval < 1)
- *newval = 1;
-
- return true;
-}
-
/*
* index_pages_fetched
* Estimate the number of pages actually fetched after accounting for
{
return ceil(relation_byte_size(tuples, width) / BLCKSZ);
}
+
+/*
+ * GUC check_hook for effective_cache_size
+ */
+bool
+check_effective_cache_size(int *newval, void **extra, GucSource source)
+{
+ /*
+ * -1 is the documented way of requesting auto-tune, but we also treat
+ * zero as meaning that, since we don't consider zero a valid setting.
+ */
+ if (*newval <= 0)
+ {
+ /*
+ * If we haven't yet changed the initial default of -1, just let it
+ * be. We'll fix it later on during GUC initialization, when
+ * set_default_effective_cache_size is called. (If we try to do it
+ * immediately, we may not be looking at the final value of NBuffers.)
+ */
+ if (effective_cache_size == -1)
+ return true;
+
+ /*
+ * Otherwise, substitute the auto-tune value, being wary of overflow.
+ */
+ if (NBuffers < INT_MAX / 4)
+ *newval = NBuffers * 4;
+ else
+ *newval = INT_MAX;
+ }
+
+ Assert(*newval > 0);
+
+ return true;
+}
+
+/*
+ * initialize effective_cache_size at the end of GUC startup
+ */
+void
+set_default_effective_cache_size(void)
+{
+ /*
+ * If the value of effective_cache_size is still -1 (or zero), replace it
+ * with the auto-tune value.
+ */
+ if (effective_cache_size <= 0)
+ {
+ /* disable the short-circuit in check_effective_cache_size */
+ effective_cache_size = 0;
+ /* and let check_effective_cache_size() compute the setting */
+ SetConfigOption("effective_cache_size", "-1",
+ PGC_POSTMASTER, PGC_S_OVERRIDE);
+ }
+ Assert(effective_cache_size > 0);
+}
projects / postgresql.git / commitdiff