Change cache hit ratio to reflect change since last snap

This fixes #272
dalibo · Jun 10, 2022 · f074d9d · f074d9d
1 parent b422649
commit f074d9d
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diff --git a/docs/man/pg_activity.1 b/docs/man/pg_activity.1
@@ -133,7 +133,7 @@
 .\" ========================================================================
 .\"
 .IX Title "PG_ACTIVITY 1"
-.TH PG_ACTIVITY 1 "2022-06-09" "pg_activity 3.0.0a1" "Command line tool for PostgreSQL server activity monitoring."
+.TH PG_ACTIVITY 1 "2022-06-10" "pg_activity 3.0.0a1" "Command line tool for PostgreSQL server activity monitoring."
 .\" For nroff, turn off justification.  Always turn off hyphenation; it makes
 .\" way too many mistakes in technical documents.
 .if n .ad l
@@ -172,8 +172,8 @@ Global :
 .IX Item "- dbs size: total size of the databases (filtered);"
 .IP "\- \fBgrowth\fR: groth in B/s of the databases (filtered);" 2
 .IX Item "- growth: groth in B/s of the databases (filtered);"
-.IP "\- \fBcache hit ratio\fR: the percentage of page read from the PostgreSQL's cache (filtered)." 2
-.IX Item "- cache hit ratio: the percentage of page read from the PostgreSQL's cache (filtered)."
+.IP "\- \fBcache hit ratio\fR: the percentage of page read from the PostgreSQL's cache since last snapshot(filtered)." 2
+.IX Item "- cache hit ratio: the percentage of page read from the PostgreSQL's cache since last snapshot(filtered)."
 .PD
 .PP
 Sessions :

diff --git a/docs/man/pg_activity.pod b/docs/man/pg_activity.pod
@@ -38,7 +38,7 @@ Global :
 
 =item - B<growth>: groth in B/s of the databases (filtered);
 
-=item - B<cache hit ratio>: the percentage of page read from the PostgreSQL's cache (filtered).
+=item - B<cache hit ratio>: the percentage of page read from the PostgreSQL's cache since last snapshot(filtered).
 
 =back
 

diff --git a/pgactivity/data.py b/pgactivity/data.py
@@ -21,6 +21,7 @@
     BlockingProcess,
     Filters,
     WaitingProcess,
+    Pct,
     RunningProcess,
     ServerInformation,
     NO_FILTER,
@@ -232,11 +233,13 @@ def pg_get_server_information(
             )
             ret = cur.fetchone()
 
+        hr: Optional[Pct] = Pct(0.0)
         tps, ips, ups, dps, rps = 0, 0, 0, 0, 0
         size_ev = 0.0
         if prev_server_info is not None:
             dt = float(ret["epoch"] - prev_server_info.epoch)
             try:
+                # Note: All this could be negative just after a stat reset
                 tps = int((ret["xact_count"] - prev_server_info.xact_count) / dt)
                 size_ev = float(ret["total_size"] - prev_server_info.total_size) / dt
                 ips = int((ret["insert"] - prev_server_info.insert) / dt)
@@ -245,6 +248,13 @@ def pg_get_server_information(
                 rps = int(
                     (ret["tuples_returned"] - prev_server_info.tuples_returned) / dt
                 )
+                deltaread = ret["blks_read"] - prev_server_info.blks_read
+                deltahit = ret["blks_hit"] - prev_server_info.blks_hit
+                hr = (
+                    Pct(100 * deltahit / (deltaread + deltahit))
+                    if deltaread + deltahit != 0
+                    else None
+                )
             except ZeroDivisionError:
                 pass
 
@@ -255,6 +265,7 @@ def pg_get_server_information(
             update_per_second=ups,
             delete_per_second=dps,
             tuples_returned_per_second=rps,
+            cache_hit_ratio_last_snap=hr,
             **ret,
         )
 

diff --git a/pgactivity/queries/get_server_info_oldest.sql b/pgactivity/queries/get_server_info_oldest.sql
@@ -9,10 +9,8 @@ WITH dbinfo AS(
                    WHEN %(skip_db_size)s THEN %(prev_total_size)s
                    ELSE SUM(pg_database_size(d.datname))
                END, 0) AS total_size,
-               COALESCE(CASE WHEN sum(sd.blks_read) + sum(sd.blks_hit) = 0
-                   THEN 0
-                   ELSE trunc(100 * sum(sd.blks_hit) / (sum(sd.blks_read) + sum(sd.blks_hit)), 2)
-               END, 0) AS cache_hit_ratio,
+               COALESCE(SUM(sd.blks_read), 0) AS blks_read,
+               COALESCE(SUM(sd.blks_hit), 0) AS blks_hit,
                COALESCE(MAX(LENGTH(d.datname)), 0) AS max_dbname_length,
                current_timestamp - pg_postmaster_start_time() AS uptime,
                EXTRACT(EPOCH FROM NOW()) AS epoch

diff --git a/pgactivity/queries/get_server_info_post_090000.sql b/pgactivity/queries/get_server_info_post_090000.sql
@@ -10,10 +10,8 @@ WITH dbinfo AS(
                    WHEN %(skip_db_size)s THEN %(prev_total_size)s
                    ELSE SUM(pg_database_size(d.datname))
                END, 0) AS total_size,
-               COALESCE(CASE WHEN sum(sd.blks_read) + sum(sd.blks_hit) = 0
-                   THEN 0
-                   ELSE trunc(100 * sum(sd.blks_hit) / (sum(sd.blks_read) + sum(sd.blks_hit)), 2)
-               END, 0) AS cache_hit_ratio,
+               COALESCE(SUM(sd.blks_read), 0) AS blks_read,
+               COALESCE(SUM(sd.blks_hit), 0) AS blks_hit,
                COALESCE(MAX(LENGTH(d.datname)), 0) AS max_dbname_length,
                current_timestamp - pg_postmaster_start_time() AS uptime,
                EXTRACT(EPOCH FROM NOW()) AS epoch

diff --git a/pgactivity/queries/get_server_info_post_090200.sql b/pgactivity/queries/get_server_info_post_090200.sql
@@ -10,10 +10,8 @@ WITH dbinfos AS(
                    WHEN %(skip_db_size)s THEN %(prev_total_size)s
                    ELSE SUM(pg_database_size(d.datname))
                END, 0) AS total_size,
-               COALESCE(CASE WHEN sum(sd.blks_read) + sum(sd.blks_hit) = 0
-                   THEN 0
-                   ELSE trunc(100 * sum(sd.blks_hit) / (sum(sd.blks_read) + sum(sd.blks_hit)), 2)
-               END, 0) AS cache_hit_ratio,
+               COALESCE(SUM(sd.blks_read), 0) AS blks_read,
+               COALESCE(SUM(sd.blks_hit), 0) AS blks_hit,
                COALESCE(MAX(LENGTH(d.datname)), 0) AS max_dbname_length,
                current_timestamp - pg_postmaster_start_time() AS uptime,
                EXTRACT(EPOCH FROM NOW()) AS epoch

diff --git a/pgactivity/queries/get_server_info_post_090400.sql b/pgactivity/queries/get_server_info_post_090400.sql
@@ -12,10 +12,8 @@ WITH dbinfo AS(
                    WHEN %(skip_db_size)s THEN %(prev_total_size)s
                    ELSE SUM(pg_database_size(d.datname))
                END, 0) AS total_size,
-               COALESCE(CASE WHEN sum(sd.blks_read) + sum(sd.blks_hit) = 0
-                   THEN 0
-                   ELSE trunc(100 * sum(sd.blks_hit) / (sum(sd.blks_read) + sum(sd.blks_hit)), 2)
-               END, 0) AS cache_hit_ratio,
+               COALESCE(SUM(sd.blks_read), 0) AS blks_read,
+               COALESCE(SUM(sd.blks_hit), 0) AS blks_hit,
                COALESCE(MAX(LENGTH(d.datname)), 0) AS max_dbname_length,
                current_timestamp - pg_postmaster_start_time() AS uptime,
                EXTRACT(EPOCH FROM NOW()) AS epoch

diff --git a/pgactivity/queries/get_server_info_post_090600.sql b/pgactivity/queries/get_server_info_post_090600.sql
@@ -14,10 +14,8 @@ WITH dbinfo AS(
                    WHEN %(skip_db_size)s THEN %(prev_total_size)s
                    ELSE SUM(pg_database_size(d.datname))
                END, 0) AS total_size,
-               COALESCE(CASE WHEN sum(sd.blks_read) + sum(sd.blks_hit) = 0
-                   THEN 0
-                   ELSE trunc(100 * sum(sd.blks_hit) / (sum(sd.blks_read) + sum(sd.blks_hit)), 2)
-               END, 0) AS cache_hit_ratio,
+               COALESCE(SUM(sd.blks_read), 0) AS blks_read,
+               COALESCE(SUM(sd.blks_hit), 0) AS blks_hit,
                COALESCE(MAX(LENGTH(d.datname)), 0) AS max_dbname_length,
                current_timestamp - pg_postmaster_start_time() AS uptime,
                EXTRACT(EPOCH FROM NOW()) AS epoch

diff --git a/pgactivity/queries/get_server_info_post_100000.sql b/pgactivity/queries/get_server_info_post_100000.sql
@@ -12,10 +12,8 @@ WITH dbinfo AS(
                    WHEN %(skip_db_size)s THEN %(prev_total_size)s
                    ELSE SUM(pg_database_size(d.datname))
                END, 0) AS total_size,
-               COALESCE(CASE WHEN sum(sd.blks_read) + sum(sd.blks_hit) = 0
-                   THEN 0
-                   ELSE trunc(100 * sum(sd.blks_hit) / (sum(sd.blks_read) + sum(sd.blks_hit)), 2)
-               END, 0) AS cache_hit_ratio,
+               COALESCE(SUM(sd.blks_read), 0) AS blks_read,
+               COALESCE(SUM(sd.blks_hit), 0) AS blks_hit,
                COALESCE(MAX(LENGTH(d.datname)), 0) AS max_dbname_length,
                current_timestamp - pg_postmaster_start_time() AS uptime,
                EXTRACT(EPOCH FROM NOW()) AS epoch

diff --git a/pgactivity/queries/get_server_info_post_110000.sql b/pgactivity/queries/get_server_info_post_110000.sql
@@ -11,10 +11,8 @@ WITH dbinfo AS(
                    WHEN %(skip_db_size)s THEN %(prev_total_size)s
                    ELSE SUM(pg_database_size(d.datname))
                END, 0) AS total_size,
-               COALESCE(CASE WHEN sum(sd.blks_read) + sum(sd.blks_hit) = 0
-                   THEN 0
-                   ELSE trunc(100 * sum(sd.blks_hit) / (sum(sd.blks_read) + sum(sd.blks_hit)), 2)
-               END, 0) AS cache_hit_ratio,
+               COALESCE(SUM(sd.blks_read), 0) AS blks_read,
+               COALESCE(SUM(sd.blks_hit), 0) AS blks_hit,
                COALESCE(MAX(LENGTH(d.datname)), 0) AS max_dbname_length,
                current_timestamp - pg_postmaster_start_time() AS uptime,
                EXTRACT(EPOCH FROM NOW()) AS epoch

diff --git a/pgactivity/queries/get_server_info_post_120000.sql b/pgactivity/queries/get_server_info_post_120000.sql
@@ -10,10 +10,8 @@ WITH dbinfo AS(
                    WHEN %(skip_db_size)s THEN %(prev_total_size)s
                    ELSE SUM(pg_database_size(d.datname))
                END, 0) AS total_size,
-               COALESCE(CASE WHEN sum(sd.blks_read) + sum(sd.blks_hit) = 0
-                   THEN 0
-                   ELSE trunc(100 * sum(sd.blks_hit) / (sum(sd.blks_read) + sum(sd.blks_hit)), 2)
-               END, 0) AS cache_hit_ratio,
+               COALESCE(SUM(sd.blks_read), 0) AS blks_read,
+               COALESCE(SUM(sd.blks_hit), 0) AS blks_hit,
                COALESCE(MAX(LENGTH(d.datname)), 0) AS max_dbname_length,
                current_timestamp - pg_postmaster_start_time() AS uptime,
                EXTRACT(EPOCH FROM NOW()) AS epoch

diff --git a/pgactivity/queries/get_server_info_post_140000.sql b/pgactivity/queries/get_server_info_post_140000.sql
@@ -10,10 +10,8 @@ WITH dbinfo AS(
                    WHEN %(skip_db_size)s THEN %(prev_total_size)s
                    ELSE SUM(pg_database_size(d.datname))
                END, 0) AS total_size,
-               COALESCE(CASE WHEN sum(sd.blks_read) + sum(sd.blks_hit) = 0
-                   THEN 0
-                   ELSE trunc(100 * sum(sd.blks_hit) / (sum(sd.blks_read) + sum(sd.blks_hit)), 2)
-               END, 0) AS cache_hit_ratio,
+               COALESCE(SUM(sd.blks_read), 0) AS blks_read,
+               COALESCE(SUM(sd.blks_hit), 0) AS blks_hit,
                COALESCE(MAX(LENGTH(d.datname)), 0) AS max_dbname_length,
                current_timestamp - pg_postmaster_start_time() AS uptime,
                EXTRACT(EPOCH FROM NOW()) AS epoch

diff --git a/pgactivity/types.py b/pgactivity/types.py
@@ -795,7 +795,8 @@ class ServerInformation:
     delete: int
     tuples_returned: int
     total_size: int
-    cache_hit_ratio: Pct = attr.ib(converter=Pct)
+    blks_read: int
+    blks_hit: int
     max_dbname_length: int
     uptime: timedelta
     epoch: int  # an epoch,  used for the calculation of the tps & size_evolution
@@ -827,6 +828,9 @@ class ServerInformation:
     update_per_second: int
     delete_per_second: int
     tuples_returned_per_second: int
+    cache_hit_ratio_last_snap: Optional[Pct] = attr.ib(
+        converter=attr.converters.optional(Pct)
+    )
 
     @property
     def worker_processes(self) -> Optional[int]:

diff --git a/pgactivity/views.py b/pgactivity/views.py
@@ -242,7 +242,7 @@ def indent(text: str) -> str:
         columns = [
             [f"* Global: {render(uptime)} uptime"],
             [f"{render(total_size)} dbs size - {render(size_ev)} growth"],
-            [f"{render(si.cache_hit_ratio)} cache hit ratio"],
+            [f"{render(si.cache_hit_ratio_last_snap)} cache hit ratio"],
         ]
         yield from render_columns(columns, delimiter=f" {term.bold_blue('⋅')} ")
 

diff --git a/tests/test_ui.txt b/tests/test_ui.txt
@@ -124,7 +124,9 @@ Force local mode and mock server and system info
 ...             xact_count=1000,
 ...             total_size=20480000,
 ...             size_evolution=1024,
-...             cache_hit_ratio=90.1222,
+...             blks_read=1,
+...             blks_hit=9,
+...             cache_hit_ratio_last_snap=90.1222,
 ...             epoch=10000,
 ...             uptime=timedelta(days=125, seconds=25, minutes=21, hours=3, weeks=1),
 ...             tps=15,

diff --git a/tests/test_views.txt b/tests/test_views.txt
@@ -98,7 +98,9 @@ Remote host:
 ...     xact_count=1000,
 ...     total_size=20480000,
 ...     size_evolution=1024,
-...     cache_hit_ratio=90.1222,
+...     blks_read=1,
+...     blks_hit=9,
+...     cache_hit_ratio_last_snap=90.1222,
 ...     epoch=10000,
 ...     uptime=timedelta(days=125, seconds=25, minutes=21, hours=3, weeks=1),
 ...     tps=15,
@@ -422,7 +424,9 @@ Tests for screen()
 ...     xact_count=1000,
 ...     total_size=20480000,
 ...     size_evolution=1024,
-...     cache_hit_ratio=90.1222,
+...     blks_read=1,
+...     blks_hit=9,
+...     cache_hit_ratio_last_snap=90.1222,
 ...     epoch=10000,
 ...     uptime=timedelta(days=125, seconds=25, minutes=21, hours=3, weeks=1),
 ...     tps=15,