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18
votes
0answers
452 views

Implementation and contraindications for OPTIMIZE_FOR_SEQUENTIAL_KEY

SQL Server 2019 CTP3.1 introduced an optimization to address last-page insert contention. This takes the form of an index option called OPTIMIZE_FOR_SEQUENTIAL_KEY. One imagines this could be an ...
13
votes
0answers
791 views

Splitting Snapshot files with MaxBCPThreads for Transactional Replication

I've just set up a publication, and I'm attempting to get the snapshot to apply faster. So far the Distribution Agent is respecting the MaxBCPThreads settings, but the Snapshot Agent is not. I'm ...
11
votes
0answers
589 views

UPDATE STATISTICS options fail in Amazon RDS SQL Server

In Amazon RDS SQL Server (any version/edition), create a temp table and update statistics on it. This works fine: IF OBJECT_ID('tempdb..#t') IS NOT NULL DROP TABLE #t; GO CREATE TABLE #t (id INT ...
9
votes
1answer
839 views

HADR high worker thread usage

Why would an availability group's number of worker threads in an HADR pool increase well beyond minimum usage of "typically, there are 3–10 shared threads" per replica? In one case we've observed ...
8
votes
0answers
192 views

What cases benefit from the Reduce, Replicate, and Redistribute join hints?

The From Clause Documentation starting with SQL Server 2008 briefly mention 3 join hints and their basic mechanisms: Reduce Replicate Redistribute However there does not seem to be much information ...
8
votes
0answers
329 views

Cardinality estimation on tables with large cardinality variance between keys

Context I have stumbled on an issue in SQL Azure where the Sort-operator is spilling over into TempDB due to poor row estimates. We are querying a master table that is joined with a number of detail ...
8
votes
4answers
1k views

Foreign Key with a Constant

Let's say I have a table A, that has two columns: one is an ID for ThingA, and one is an ID for ThingB. The primary key is (ThingA, ThingB). Next, I have a second table, but this time it's restricted ...
8
votes
0answers
620 views

Why does RDS PostgreSQL always recover on restart?

I am running an RDS instance of PostgreSQL 9.6.3: select version(); returns PostgreSQL 9.6.3 on x86_64-pc-linux-gnu [...]. I have found that after issuing a stop from the RDS console followed by a ...
8
votes
2answers
23k views

Why does CAST(1 AS SIGNED INTEGER) return a BIGINT on MySQL?

If I do CAST(1 AS SIGNED INTEGER) I always end up getting a BIGINT returned, for example: $ mysql -u root -p --column-type-info Enter password: --- Copyright and help message snipped for brevity --- ...
7
votes
0answers
359 views

Database Stuck 'In Recovery' with command XTP_DB_RECOVERY

We recently converted a table to memory optimized data. Our backups have all ballooned (3x300GB files to 3x600GB files for Full, 3x50GB to 3x250GB for Diffs), and startup has been getting ...
7
votes
0answers
171 views

Constant Scan applying

This question is continuation of optimizer behavior exploration in regard to VALUES construct started here and here. I want to ask about VALUES and APPLY this time. Using CROSS APPLY to alias an ...
7
votes
0answers
145 views

CMEMTHREAD waits during Index Optimisation in Availability Group

In a 3 node Availability group, a secondary replica will often become subject to redo lag due to the causes covered in Microsoft's documentation: Troubleshoot: Changes on the Primary Replica are not ...
7
votes
0answers
222 views

SQL Server 2016 & 2017 Force Plan failing with reason 8695

I'm trying to force a plan using query store but it keeps failing with reason 8695 according to data in SYS.QUERY_STORE_PLAN the last_force_failure_reason_desc is 'General_Failure'. Does anyone know ...
7
votes
1answer
667 views

Convert query in words to relational algebra

I have a follow-up question to a question I have previously asked on SO. Instead of the query from my initial question, I want to convert the following into relational algebra: List the names and ...
7
votes
1answer
818 views

Oracle Ref Partitioning: Deadlock due to child table row migration

My ordering application uses Oracle 11g Database. This DB has a primary table ORDERS and multiple child tables like ORDER_DETAILS, PLAN etc. ORDERS table is LIST partitioned on STATUS column and all ...
7
votes
0answers
12k views

Conceptual data model for a billing system

I am working on existing MySQL database. My task is to create a new data model for a billing system on that existing application. I have created a conceptual data model (click to enlarge): ...
7
votes
2answers
3k views

verify that mongos server is connected to config servers

I've been writing a backup script for sharded replica-sets and it's almost done, except that I can't seem to get it to successfully start the balancer back up after everything's all said and done. ...
7
votes
1answer
587 views

SSMS 2014 (and 2012) CTRL+TAB requires pressing enter

Sometime last week my CTRL+TAB behavior changed. I used to hit CTRL+TAB, release, then I would be in my previous document tab. Now I hit CTRL+TAB, release, and the nav window is still open requiring ...
6
votes
0answers
36 views

Efficiently store large list structure in RocksDB so that the data can be retrieved in pages

Description: RocksDB is a key-value storage so we can simply serialise the list of objects & store the value corresponding to a key. This would be ok if the data in the list is small enough. ...
6
votes
0answers
96 views

Can oscillating number of fragment decrease FTS query performance?

I've got a FTS Catalog on a table containing ~106 row. It used to work like a charm, but lately, for an unknown reason it started to get very bad (query >30 sec) performances randomly. Reading ...
6
votes
0answers
1k views

Alwayson AG lease timeout and healthcheck timeout

We have a physical SQL Server 2016 Enterprise SP2 with two instances and each instance contains one AG. Sometimes it happens that one AG goes to resolving (without failover), the cluster resource is ...
6
votes
0answers
218 views

SQL Server 2012+ & Service Broker: SSBDT Spam ending conversations after sending message to NULL conversation_handle

I'm mostly posting this for community awareness, but feel free to give feedback if you think there is a solution other than coding around the problem as we are doing. Crossposting this from my bug ...
6
votes
0answers
149 views

dm_os_memory_cache_clock_hands understanding

As I mentioned in this question I'm trying to understand the working of clock hands. Simply put clock hands move when there is memory pressure so that cache entries can be removed or the cost can be ...
6
votes
0answers
2k views

Working on a decision tree database design

I'm doing the conceptual model for a Decision tree database. The goal is store any Decision tree. I have four entity types: DecisionTree, Node, Branch and Leaf. Each Decision tree is composed of ...
6
votes
0answers
310 views

SQL Server Profiler: why the RPC Starting event does use an different decimal separator from SP Starting?

Trying to diagnose an problem, I've ran into that inconsistency. In SQL Server Profiler, the RPC Starting event uses the regional settings to write real numbers (example: in Portuguese(Brazil) 14.5 ...
6
votes
0answers
437 views

CHANGE_TRACKING_CURRENT_VERSION() incorrect on database in standby

We are using a change tracking solution to export increments for BI purposes for years now. But it was running directly on the production database. To lower the load on the system we wanted it to run ...
6
votes
4answers
1k views

SQL Server Select Query Is Slow Even With NC-Index and Full-Text Index

I am attempting to query a maximum of 65,000 records in a database (minimum of 0). The server is using MS SQL Server 2014, and I have no way to change the hardware on the server. Schema [Id] (PK) ...
6
votes
1answer
1k views

How can I determine why a concurrent Postgres index was marked as INVALID?

I'm trying to create an index concurrently. CREATE INDEX CONCURRENTLY blocks_expr_idx6 ON blocks USING btree ('blah') WHERE "type" = 'user root'; 12 hours after I ran the query, if I run \d blocks ...
6
votes
0answers
1k views

Why does pg_last_xact_replay_timestamp() sometimes return extremely old timestamps?

In PostgreSQL 9.5, to monitor streaming replication lag, I use a combination of: pg_current_xlog_location() pg_last_xlog_replay_location() pg_last_xact_replay_timestamp() The first two functions are ...
6
votes
1answer
509 views

Postgresql with just index storage

I have a PostgreSQL table with a key (bigint) and a value (double). The table has tens of billions of rows. I have a single btree on the (key,value) for aid lookups by key. The table is never updated. ...
6
votes
1answer
1k views

DB snapshot goes into SUSPECT mode (SQL 2014 on WIN2K8R2)

I was hoping someone here might have encountered this sort of issue and if so what did you do to fix it? Here's some details: DB server: SQL 2014 Enterprise (12.0.4100.1) OS: Windows 2008R2 ...
6
votes
0answers
392 views

Roles and policies in Postgresql 9.5 row-level security

Following the the info in posts like these i would like to use the role system and policies, i.e. each user in my system would have a db role. I want to model the following properties but i can't come ...
6
votes
1answer
77 views

Does MySQL/InnoDB use table caches when dealing with foreign tables?

TL;DR: Does a table referred to via schema.table get held in table cache? I have a large number of client databases that our application connects to based on an http request. These are used for every ...
6
votes
1answer
1k views

Change Tracking across several Tables

I'm looking into providing DB level change tracking within my system. I need to be able to track changes at an entity level, rather than just individual tables. Right now, we have triggers on each of ...
6
votes
1answer
984 views

Select * from statement execute very slowly, innodb io read speed is low

I have a very simple query " select * from ap_statistic " running in my servers. the servers have the same hardware and software configuration (CPU 8 core, mem :32G, OS: redhat 5.5, mysql version: 5....
6
votes
1answer
599 views

Where can I find the SQL-89 standard?

This question is different but similar to this request looking for SQL-86. SQL 1989 is almost 30 years old. Is this spec freely available anywhere. The standard does not have a Wikipage or the like? ...
6
votes
2answers
94 views

Changes access method for non-correlated subquery

Oracle 11g R2 Unfortunately our application has per row security "features". We have a query that looks about like this: Bad, slow: SELECT someRow, someOtherRow FROM bigTableA a WHERE EXISTS ( ...
5
votes
1answer
2k views

ERD for a web development company

I am working on an ERD which represents the relationships between entities in a Web development company behavioral model. There I have entities like: Customer Service ----------- (like: web ...
5
votes
0answers
69 views

What are the downsides of running DBCC FREESYSTEMCACHE ('TokenAndPermUserStore') hourly?

I have been seeing some concerning behavior in the SQL Server memory caches on one of our production servers. We are on SQL Server 2014 SP2 Enterprise Edition, 16 cores, 400GB RAM (300 GB dedicated to ...
5
votes
2answers
201 views

Solving supertype-subtype relationship without sacrificing data consistency in a relational database

Trying to get better at designing databases, I noticed I'm always stuck trying to solve variations of the exact same problem. Here is an example using common requirements: An online store sells ...
5
votes
0answers
346 views

How do I identify the source of the 17886 errors (“server will drop the connection”) in my SQL errorlog?

I have a SQL 2012 server that is throwing the following error every 5 minutes or so: Error: 17886, Severity: 20, State: 1. The server will drop the connection, because the client driver has ...
5
votes
1answer
571 views

Test Driven Design for postgres procedures

I am looking to introduce a test driven design style to writing my stored procedures for a postgresql database implementation. I have seen that pgTap is a popular unit testing tool for postgres and ...
5
votes
0answers
166 views

Using the Schema Generation Wizard to regenerate a previously-generated schema

Lately, I've been trying to clean up a group of projects that my company received from an outside contractor. Among them is an SSAS cube, with an associated data warehouse. The contractors generated ...
5
votes
1answer
493 views

How to limit work_mem on PostgreSQL

As an analyst I love having the ability to turn up the work_mem on occasion when a big sort or index build is in the offing. As a DBA, the idea of random users being able to request an arbitrarily ...
5
votes
0answers
452 views

Postgres 10 Logical Replication without truncating existing table

I have been fooling around with Postgres 10 logical replication, trying to learn about it and potentially apply it to a couple of projects. I have observed something that I am wondering about, but I ...
5
votes
0answers
230 views

UUID V1 and V4 bloats substantially after sequntial inserts and deletes. Why is it so, compared to serial and temporal BTree (which does not bloat)?

I am trying to understand the impact of deletions to bloat of tables and indexes after large number of inserts and deletes. The inserts and deletes are following a rather strict pattern: first the ...
5
votes
2answers
585 views

Deleting data from a table containing LOBs did not reduce the amount of data reported INTERNALLY by the table or database

Running SQL Server 2012 standard, using both replication data and log shipping. Transaction log backups are created every few minutes. This question is NOT about the amount of space reported by the ...
5
votes
1answer
3k views

ORA-04091: table ExpenseTable is mutating, trigger/function may not see it

I have two tables and a trigger and am inserting values in ProjectsTable like this: CREATE TABLE ProjectsTable ( ProjectID NUMBER(6) NOT NULL, ProjectName VARCHAR2(200) NOT NULL, Cost ...
5
votes
0answers
110 views

Deadlock in REDO thread , 1 replica went OK other didn't?

I have a 3 node cluster and the 2 secondaries initially went into SUSPECT mode due to a deadlock. I tried to resume both and only one caught up while the other is continuously deadlocking. I have to ...
5
votes
1answer
662 views

How to Achieve Concurrent Write Transactions to MySQL Group Replication in Multi-Primary Mode

I've set up a MySQL "cluster" (four CentOS 7 servers running MySQL 5.7.19) using Group Replication in multi-primary mode, but I can't get it to accept writes from more than one thread at a time. This ...

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