postgres.git / summary / log / commit / refs
commit 2fb9fb6614f5aa92271e9d4eef9a192cdf6c468e
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu May 29 17:51:09 2014 +0000
First released in: 9.4.0, 8.4.22, 9.0.18, 9.1.14, 9.2.9, 9.3.5
When using the OSSP UUID library, cache its uuid_t state object.
The original coding in contrib/uuid-ossp created and destroyed a uuid_t
object (or, in some cases, even two of them) each time it was called.
This is not the intended usage: you're supposed to keep the uuid_t object
around so that the library can cache its state across uses. (Other UUID
libraries seem to keep equivalent state behind-the-scenes in static
variables, but OSSP chose differently.) Aside from being quite inefficient,
creating a new uuid_t loses knowledge of the previously generated UUID,
which in theory could result in duplicate V1-style UUIDs being created
on sufficiently fast machines.
On at least some platforms, creating a new uuid_t also draws some entropy
from /dev/urandom, leaving less for the rest of the system. This seems
sufficiently unpleasant to justify back-patching this change.
contrib/uuid-ossp/uuid-ossp.c | 74 +++++++++++++++++++++++++------------------
1 file changed, 44 insertions(+), 30 deletions(-)
diff --git a/contrib/uuid-ossp/uuid-ossp.c b/contrib/uuid-ossp/uuid-ossp.c
index d4fc62bd4f3..71bdfa15fa3 100644
--- a/contrib/uuid-ossp/uuid-ossp.c
+++ b/contrib/uuid-ossp/uuid-ossp.c
@@ -79,6 +79,42 @@ pguuid_complain(uuid_rc_t rc)
errmsg("OSSP uuid library failure: error code %d", rc)));
}
+/*
+ * We create a uuid_t object just once per session and re-use it for all
+ * operations in this module. OSSP UUID caches the system MAC address and
+ * other state in this object. Reusing the object has a number of benefits:
+ * saving the cycles needed to fetch the system MAC address over and over,
+ * reducing the amount of entropy we draw from /dev/urandom, and providing a
+ * positive guarantee that successive generated V1-style UUIDs don't collide.
+ * (On a machine fast enough to generate multiple UUIDs per microsecond,
+ * or whatever the system's wall-clock resolution is, we'd otherwise risk
+ * collisions whenever random initialization of the uuid_t's clock sequence
+ * value chanced to produce duplicates.)
+ *
+ * However: when we're doing V3 or V5 UUID creation, uuid_make needs two
+ * uuid_t objects, one holding the namespace UUID and one for the result.
+ * It's unspecified whether it's safe to use the same uuid_t for both cases,
+ * so let's cache a second uuid_t for use as the namespace holder object.
+ */
+static uuid_t *
+get_cached_uuid_t(int which)
+{
+ static uuid_t *cached_uuid[2] = {NULL, NULL};
+
+ if (cached_uuid[which] == NULL)
+ {
+ uuid_rc_t rc;
+
+ rc = uuid_create(&cached_uuid[which]);
+ if (rc != UUID_RC_OK)
+ {
+ cached_uuid[which] = NULL;
+ pguuid_complain(rc);
+ }
+ }
+ return cached_uuid[which];
+}
+
static char *
uuid_to_string(const uuid_t *uuid)
{
@@ -109,20 +145,14 @@ string_to_uuid(const char *str, uuid_t *uuid)
static Datum
special_uuid_value(const char *name)
{
- uuid_t *uuid;
+ uuid_t *uuid = get_cached_uuid_t(0);
char *str;
uuid_rc_t rc;
- rc = uuid_create(&uuid);
- if (rc != UUID_RC_OK)
- pguuid_complain(rc);
rc = uuid_load(uuid, name);
if (rc != UUID_RC_OK)
pguuid_complain(rc);
str = uuid_to_string(uuid);
- rc = uuid_destroy(uuid);
- if (rc != UUID_RC_OK)
- pguuid_complain(rc);
return DirectFunctionCall1(uuid_in, CStringGetDatum(str));
}
@@ -166,20 +196,14 @@ uuid_ns_x500(PG_FUNCTION_ARGS)
static Datum
uuid_generate_internal(int mode, const uuid_t *ns, const char *name)
{
- uuid_t *uuid;
+ uuid_t *uuid = get_cached_uuid_t(0);
char *str;
uuid_rc_t rc;
- rc = uuid_create(&uuid);
- if (rc != UUID_RC_OK)
- pguuid_complain(rc);
rc = uuid_make(uuid, mode, ns, name);
if (rc != UUID_RC_OK)
pguuid_complain(rc);
str = uuid_to_string(uuid);
- rc = uuid_destroy(uuid);
- if (rc != UUID_RC_OK)
- pguuid_complain(rc);
return DirectFunctionCall1(uuid_in, CStringGetDatum(str));
}
@@ -202,25 +226,15 @@ uuid_generate_v1mc(PG_FUNCTION_ARGS)
static Datum
uuid_generate_v35_internal(int mode, pg_uuid_t *ns, text *name)
{
- uuid_t *ns_uuid;
- Datum result;
- uuid_rc_t rc;
+ uuid_t *ns_uuid = get_cached_uuid_t(1);
- rc = uuid_create(&ns_uuid);
- if (rc != UUID_RC_OK)
- pguuid_complain(rc);
- string_to_uuid(DatumGetCString(DirectFunctionCall1(uuid_out, UUIDPGetDatum(ns))),
+ string_to_uuid(DatumGetCString(DirectFunctionCall1(uuid_out,
+ UUIDPGetDatum(ns))),
ns_uuid);
- result = uuid_generate_internal(mode,
- ns_uuid,
- text_to_cstring(name));
-
- rc = uuid_destroy(ns_uuid);
- if (rc != UUID_RC_OK)
- pguuid_complain(rc);
-
- return result;
+ return uuid_generate_internal(mode,
+ ns_uuid,
+ text_to_cstring(name));
}
[parent: 952b036054d7]