Trace reads at different consistency levels
Running and tracing queries that read data at different consistency levels.
After performing the setup steps, run and trace queries that read data at different consistency levels. The tracing output shows that using three replicas on a five-node cluster, a consistency level of ONE processes responses from one of three replicas, QUORUM from two of three replicas, and ALL from three of three replicas.
Procedure
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Connect cqlsh to the first node in the ring.
ccm node1 cqlsh
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On the cqlsh command line, create a keyspace that specifies using three replica
for data distribution in the cluster.
cqlsh> CREATE KEYSPACE demo_cl WITH replication = {'class':'SimpleStrategy', 'replication_factor':3}; -
In the three-replica keyspace, create a table, and insert some values:
cqlsh> USE demo_cl; cqlsh:demo_cl> CREATE TABLE demo_table ( id int PRIMARY KEY, col1 int, col2 int ); cqlsh:demo_cl> INSERT INTO demo_table (id, col1, col2) VALUES (0, 0, 0); -
Turn on tracing and use the CONSISTENCY command to check that the
consistency level is ONE, the default.
cqlsh:demo_cl> TRACING on; cqlsh:demo_cl> CONSISTENCY;The output should be:Current consistency level is 1. -
Query the table to read the value of the primary key.
cqlsh:demo_cl> SELECT * FROM demo_table WHERE id = 0;The output includes tracing information:id | col1 | col2 ----+------+------ 0 | 0 | 0 (1 rows) Tracing session: 0f5058d0-6761-11e4-96a3-fd07420471ed activity | timestamp | source | source_elapsed -------------------------------------------------------------------------------------------------+----------------------------+-----------+---------------- Execute CQL3 query | 2014-11-08 08:05:29.437000 | 127.0.0.1 | 0 Parsing SELECT * FROM demo_table WHERE id = 0 LIMIT 10000; [SharedPool-Worker-1] | 2014-11-08 08:05:29.438000 | 127.0.0.1 | 820 Preparing statement [SharedPool-Worker-1] | 2014-11-08 08:05:29.438000 | 127.0.0.1 | 1637 Sending message to /127.0.0.3 [WRITE-/127.0.0.3] | 2014-11-08 08:05:29.439000 | 127.0.0.1 | 2211 Sending message to /127.0.0.4 [WRITE-/127.0.0.4] | 2014-11-08 08:05:29.439000 | 127.0.0.1 | 2237 Message received from /127.0.0.1 [Thread-10] | 2014-11-08 08:05:29.441000 | 127.0.0.3 | 75 Executing single-partition query on demo_table [SharedPool-Worker-1] | 2014-11-08 08:05:29.441000 | 127.0.0.4 | 818 Acquiring sstable references [SharedPool-Worker-1] | 2014-11-08 08:05:29.441000 | 127.0.0.4 | 861 Merging memtable tombstones [SharedPool-Worker-1] | 2014-11-08 08:05:29.441000 | 127.0.0.4 | 915 Skipped 0/0 non-slice-intersecting sstables, included 0 due to tombstones [SharedPool-Worker-1] | 2014-11-08 08:05:29.442000 | 127.0.0.4 | 999 Merging data from memtables and 0 sstables [SharedPool-Worker-1] | 2014-11-08 08:05:29.442000 | 127.0.0.4 | 1018 Merging memtable tombstones [SharedPool-Worker-1] | 2014-11-08 08:05:29.442000 | 127.0.0.3 | 1058 Skipped 0/0 non-slice-intersecting sstables, included 0 due to tombstones [SharedPool-Worker-1] | 2014-11-08 08:05:29.442000 | 127.0.0.3 | 1146 Merging data from memtables and 0 sstables [SharedPool-Worker-1] | 2014-11-08 08:05:29.442000 | 127.0.0.3 | 1165 Read 1 live and 0 tombstoned cells [SharedPool-Worker-1] | 2014-11-08 08:05:29.442000 | 127.0.0.3 | 1223 Enqueuing response to /127.0.0.1 [SharedPool-Worker-1] | 2014-11-08 08:05:29.442001 | 127.0.0.3 | 1504 Message received from /127.0.0.4 [Thread-7] | 2014-11-08 08:05:29.443000 | 127.0.0.1 | 6399 Sending message to /127.0.0.1 [WRITE-/127.0.0.1] | 2014-11-08 08:05:29.443000 | 127.0.0.3 | 1835 Message received from /127.0.0.3 [Thread-8] | 2014-11-08 08:05:29.443000 | 127.0.0.1 | 6449 Processing response from /127.0.0.4 [SharedPool-Worker-2] | 2014-11-08 08:05:29.443000 | 127.0.0.1 | 6623 Processing response from /127.0.0.3 [SharedPool-Worker-3] | 2014-11-08 08:05:29.443000 | 127.0.0.1 | 6635 Request complete | 2014-11-08 08:05:29.443897 | 127.0.0.1 | 6897 -
Change the consistency level to QUORUM and run the SELECT statement
again.
cqlsh:demo_cl> CONSISTENCY quorum; cqlsh:demo_cl> SELECT * FROM demo_table WHERE id = 0;id | col1 | col2 ----+------+------ 0 | 0 | 0 (1 rows) Tracing session: 3bbae430-6761-11e4-96a3-fd07420471ed activity | timestamp | source | source_elapsed -------------------------------------------------------------------------------------------------+----------------------------+-----------+---------------- Execute CQL3 query | 2014-11-08 08:06:43.955000 | 127.0.0.1 | 0 Parsing SELECT * FROM demo_table WHERE id = 0 LIMIT 10000; [SharedPool-Worker-1] | 2014-11-08 08:06:43.955000 | 127.0.0.1 | 71 Preparing statement [SharedPool-Worker-1] | 2014-11-08 08:06:43.955000 | 127.0.0.1 | 267 Sending message to /127.0.0.4 [WRITE-/127.0.0.4] | 2014-11-08 08:06:43.956000 | 127.0.0.1 | 1628 Sending message to /127.0.0.5 [WRITE-/127.0.0.5] | 2014-11-08 08:06:43.956000 | 127.0.0.1 | 1690 Message received from /127.0.0.1 [Thread-9] | 2014-11-08 08:06:43.957000 | 127.0.0.5 | 95 Executing single-partition query on demo_table [SharedPool-Worker-2] | 2014-11-08 08:06:43.957000 | 127.0.0.4 | 229 Acquiring sstable references [SharedPool-Worker-2] | 2014-11-08 08:06:43.957000 | 127.0.0.4 | 249 Merging memtable tombstones [SharedPool-Worker-2] | 2014-11-08 08:06:43.957000 | 127.0.0.4 | 299 Skipped 0/0 non-slice-intersecting sstables, included 0 due to tombstones [SharedPool-Worker-2] | 2014-11-08 08:06:43.957000 | 127.0.0.4 | 387 Merging data from memtables and 0 sstables [SharedPool-Worker-2] | 2014-11-08 08:06:43.957000 | 127.0.0.4 | 408 Read 1 live and 0 tombstoned cells [SharedPool-Worker-2] | 2014-11-08 08:06:43.957000 | 127.0.0.4 | 469 Enqueuing response to /127.0.0.1 [SharedPool-Worker-2] | 2014-11-08 08:06:43.957001 | 127.0.0.4 | 734 Sending message to /127.0.0.1 [WRITE-/127.0.0.1] | 2014-11-08 08:06:43.957001 | 127.0.0.4 | 894 Message received from /127.0.0.4 [Thread-7] | 2014-11-08 08:06:43.958000 | 127.0.0.1 | 3383 Processing response from /127.0.0.4 [SharedPool-Worker-2] | 2014-11-08 08:06:43.958000 | 127.0.0.1 | 3612 Executing single-partition query on demo_table [SharedPool-Worker-1] | 2014-11-08 08:06:43.959000 | 127.0.0.5 | 1462 Acquiring sstable references [SharedPool-Worker-1] | 2014-11-08 08:06:43.959000 | 127.0.0.5 | 1509 Merging memtable tombstones [SharedPool-Worker-1] | 2014-11-08 08:06:43.959000 | 127.0.0.5 | 1569 Skipped 0/0 non-slice-intersecting sstables, included 0 due to tombstones [SharedPool-Worker-1] | 2014-11-08 08:06:43.959000 | 127.0.0.5 | 1662 Merging data from memtables and 0 sstables [SharedPool-Worker-1] | 2014-11-08 08:06:43.959000 | 127.0.0.5 | 1681 Read 1 live and 0 tombstoned cells [SharedPool-Worker-1] | 2014-11-08 08:06:43.959000 | 127.0.0.5 | 1760 Enqueuing response to /127.0.0.1 [SharedPool-Worker-1] | 2014-11-08 08:06:43.959001 | 127.0.0.5 | 2104 Message received from /127.0.0.5 [Thread-10] | 2014-11-08 08:06:43.960000 | 127.0.0.1 | 5330 Sending message to /127.0.0.1 [WRITE-/127.0.0.1] | 2014-11-08 08:06:43.960000 | 127.0.0.5 | 2423 Processing response from /127.0.0.5 [SharedPool-Worker-2] | 2014-11-08 08:06:43.960000 | 127.0.0.1 | 5519 Request complete | 2014-11-08 08:06:43.960947 | 127.0.0.1 | 5947 -
Change the consistency level to ALL and run the SELECT statement again.
cqlsh:demo_cl> CONSISTENCY ALL; cqlsh:demo_cl> SELECT * FROM demo_table WHERE id = 0;id | col1 | col2 ----+------+------ 0 | 0 | 0 (1 rows) Tracing session: 4da75ca0-6761-11e4-96a3-fd07420471ed activity | timestamp | source | source_elapsed -------------------------------------------------------------------------------------------------+----------------------------+-----------+---------------- Execute CQL3 query | 2014-11-08 08:07:14.026000 | 127.0.0.1 | 0 Parsing SELECT * FROM demo_table WHERE id = 0 LIMIT 10000; [SharedPool-Worker-1] | 2014-11-08 08:07:14.026000 | 127.0.0.1 | 73 Preparing statement [SharedPool-Worker-1] | 2014-11-08 08:07:14.026000 | 127.0.0.1 | 271 Sending message to /127.0.0.4 [WRITE-/127.0.0.4] | 2014-11-08 08:07:14.027000 | 127.0.0.1 | 978 Message received from /127.0.0.1 [Thread-9] | 2014-11-08 08:07:14.027000 | 127.0.0.5 | 56 Sending message to /127.0.0.5 [WRITE-/127.0.0.5] | 2014-11-08 08:07:14.027000 | 127.0.0.1 | 1012 Executing single-partition query on demo_table [SharedPool-Worker-2] | 2014-11-08 08:07:14.027000 | 127.0.0.3 | 253 Sending message to /127.0.0.3 [WRITE-/127.0.0.3] | 2014-11-08 08:07:14.027000 | 127.0.0.1 | 1054 Acquiring sstable references [SharedPool-Worker-2] | 2014-11-08 08:07:14.027000 | 127.0.0.3 | 275 Merging memtable tombstones [SharedPool-Worker-2] | 2014-11-08 08:07:14.027000 | 127.0.0.3 | 344 Skipped 0/0 non-slice-intersecting sstables, included 0 due to tombstones [SharedPool-Worker-2] | 2014-11-08 08:07:14.028000 | 127.0.0.3 | 438 Acquiring sstable references [SharedPool-Worker-1] | 2014-11-08 08:07:14.028000 | 127.0.0.5 | 461 Merging memtable tombstones [SharedPool-Worker-1] | 2014-11-08 08:07:14.028000 | 127.0.0.5 | 525 Skipped 0/0 non-slice-intersecting sstables, included 0 due to tombstones [SharedPool-Worker-1] | 2014-11-08 08:07:14.028000 | 127.0.0.5 | 622 Merging data from memtables and 0 sstables [SharedPool-Worker-1] | 2014-11-08 08:07:14.028000 | 127.0.0.5 | 645 Read 1 live and 0 tombstoned cells [SharedPool-Worker-1] | 2014-11-08 08:07:14.028000 | 127.0.0.5 | 606 Enqueuing response to /127.0.0.1 [SharedPool-Worker-1] | 2014-11-08 08:07:14.028001 | 127.0.0.5 | 1125 Message received from /127.0.0.3 [Thread-8] | 2014-11-08 08:07:14.029000 | 127.0.0.1 | 3224 Sending message to /127.0.0.1 [WRITE-/127.0.0.1] | 2014-11-08 08:07:14.029000 | 127.0.0.5 | 1616 Processing response from /127.0.0.3 [SharedPool-Worker-3] | 2014-11-08 08:07:14.029000 | 127.0.0.1 | 3417 Message received from /127.0.0.5 [Thread-10] | 2014-11-08 08:07:14.029000 | 127.0.0.1 | 3454 Message received from /127.0.0.4 [Thread-7] | 2014-11-08 08:07:14.029000 | 127.0.0.1 | 3516 Processing response from /127.0.0.5 [SharedPool-Worker-2] | 2014-11-08 08:07:14.029000 | 127.0.0.1 | 3627 Processing response from /127.0.0.4 [SharedPool-Worker-2] | 2014-11-08 08:07:14.030000 | 127.0.0.1 | 3688 Request complete | 2014-11-08 08:07:14.030347 | 127.0.0.1 | 4347