Implementing System Versioned Temporal Table
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Temesgen Mamo, Surafel
SQL standard 2011 introduce a temporal table concept which describe a table that store data with respect to time instance. It has two part application time period table and system versioned temporal table. An application time period are for meeting the requirements of applications based on application specific time periods which is valid in the business world rather than on the basis of the time it was entered in the database and system versioned temporal table state about the retention of old data alone with current data automatically by database management system and ability of queering both current and history data. A table can also be both a system versioned table and an application time period table.
 Hello everybody, this is my presentation on implementing system variant temporal table. It includes everything about system variant temporal table, starting from what it is up to its implementation. If anyone wanted to have this slide, I uploaded it to my PGCon account, so it is available on conference websites. First, a few things about me. My name is Suraf El-Tamaskan. Currently, I am working as a DBA. I also have a work experience on full stack web application development, and starting from the last one or two years, I am participating on PostgreSQL development. My latest contribution is adding with style option to FIrst close. It is on PostgreSQL 13, and I can be found on Twitter at space file address on the screen, but I didn't tweet much yet. In this presentation, first we will see the definition of system version temporal table, and how it differs from other temporal table kind. And then we will see the application of it. In PostgreSQL, we have at least two options to implement system version table. One is using two table for storing, one for current data, and the other one for history data. Another alternative is using one table for storing both current and history card. I will talk about both options and the advantage of implementing it using one table approach. Finally, we will talk about using syntax and their function that system version temporal table will introduce. System version temporal table is introduced to SQL standard along with application time period and other temporal specification in 2011 release. It is about the retention of deleted record along with current one automatically by database management system and the ability of creating both current and history record. And there are application time period which are for meeting business model, having time varying information, and it is managed by user rather than by database system. And it is legal to have both system version and application time period in a single table. We can use system version temporal table for that sake of easily recovering from accidental data modification. If we enable system versioning to the table, we can go back to any point in time using SQL query. We can also use it for auditing to check how things look like in the past. And other interesting use cases to model reality in place of application time period. If model reality changes at the same time with database modification, we can use system version temporal table because it have advantage of maintaining by the system automatically. We can also use it to analyze how things look like over time. In post-release SQL, we have at least two design for implementing system version temporal table. One is on wiki page that describe implementing using two tables. One for history data and the other for current data. But I don't go with this approach because I don't know why I feel in most parts. I propose to implement it using only one table for storing both current and history record. And it is on current commit feast. I will talk about both approach and I describe more on my approach and its advantage. Two table approach involves two tables. One for current data storage and the other for history data. One big advantage of this approach is non temporal query which are the frequent query performance didn't affect by history data because it's only access current table. But nowadays we can achieve similar performance by partitioning. And in this approach all the record generated by delay and update operation inserted to history table using trigger and multiple common have to create implicitly to make correlation between current and history record. In one table approach both current and history data stores in one table. It uses end time column and value to classify the record. If the value is infinity it is current record. Otherwise it's related at a specified time in the time column. And system version the table treats like a kind of generated column in its implementation. Because the syntax is similar and generated column passed the test of time and the result of non temporal query doesn't have to include or consider history record. So filter codes will be added to such kind of query implicitly. There are two create system version table. There are two option to create system version table. If it is okay to use default system version in column names. Just adding with system version keyword at the end of table definitions. Enough. It enables system versioning with default system versioning column name. But if you wanted to use different name for system versioning column name we have to use X standard option as specified on the screen. Stay two time stamp with time zone column with generated always as the start and end time specification. In my implementation both current and history data stores in one table. But it's perfectly legal to have multiple record having the same primary and unique key value in the past. The conisterant only have to be observed on current data or current records. And in order to allow this happen raw in the time column is added to primary and unique key conisterant implicitly. Because in current record raw in the time column and values always infinity. So that force primary and unique key value to be unique across current record. But in history record raw in the time column and values different. So primary and unique key value can be repeated. In that system versioning column set automatically. Raw start time will be set to current transaction time. And raw end time column will be set to infinity. Here there are opinion on the appropriateness of setting raw end time column value to infinity. If we take this value literally it means raw will be current until infinity. But it's not true. The record will be removed sometimes before infinity. More meaningful values to store variable now. Which have the meaning the meaning data is current until now. But which I think it is more appropriate value. But storeable now variable didn't exist. So even SQL standard stay to use longest date data type value. In postgres SQL it is infinity. Normally update didn't occur in place. So it's performed by marking the tuple to be update to delete. That can be actually removed by other process. And then insert the updated tuple into the table. But for system versioned temporal table implementation delete tuple will be inserted back with raw end time column value set to current transaction time. Not make the record history record and insert the updates tuple by making it counter-recount by setting raw start time column value to current transaction time and end time column value to infinity. In delete the record didn't actually removed. Instead it's inserted back with raw end time column value set to current transaction time. Not in the record being current record. In select non temporal carry should not incorporate or consider history record. So history data filter close added to it implicitly. Advantage of one table approach. Well table is not any complex than non temporal table alter operation. But in two table approach modification in current table should have to propagate to history table and other advantages there is no need of technical column to correlate between history and current data. And if we support implicit updates for marking deleted tuple as a history data we can enjoy many optimization. Because there will be no need of vacuum exit for freezing and the data will be stored sorted by raw start and end time column automatically. So we can harness multiple optimization for temporal query processing on this behavior. The first form of temporal query is for system time as of close. It is used when there is a need to see the table at specified point in time in the past. It returns all the record current at specified point in time which means column and value less than specified point in time and which means raw start time column and value less than specified point in time and raw end time column and value greater or equal to specified point in time value will be returned and the syntax is specified on the screen. The other form is form close which returns all the record current within specified time rate including time point one that's excluding time point two. In closing it is the same as form close except it includes the record current at time point two. So it is the only difference from closes. It includes in time point two its return value. Between asymmetric closes is the same as between symmetric or between close. It is just more descriptive and between symmetric close here the order of time point specification is not matter because it work by picking the least time point and return the record up to and including the greater time point. There are a new syntax introduced to enable system versioning to existing table which is alter table add system versioning. It use default system versioning column and name and if the table content data it will be marked to current data by setting raw start time column and value to current transaction time and or in the time column value to infinity. If we want to use different column and name for system versioning we can do it by issuing add column and statement to raw start and end time column with the desired column and name in one command as seen on the screen. But it is forbidden to issue add column and command separately because it leaves system versioning in unusable state. If we want to if we don't want system versioning number or if we want to delete history data up to now we can issue drop system versioning to the table that drop system versioning column along with history data. We can use it with add system versioning command to limit the growth of system version table. And here are other alternative command to disable system versioning. So if anyone want to look at the patch and review it is on current commit fist please review if possible. Thanks.
 Hello everybody, this is my presentation on implementing system variant temporal table.  It includes everything about system variant temporal table, starting from what it is up  to its implementation.  If anyone wanted to have this slide, I uploaded it to my PGCon account, so it is available  on conference websites.  First, a few things about me.  My name is Suraf El-Tamaskan.  Currently, I am working as a DBA.  I also have a work experience on full stack web application development, and starting  from the last one or two years, I am participating on PostgreSQL development.  My latest contribution is adding with style option to FIrst close.  It is on PostgreSQL 13, and I can be found on Twitter at space file address on the screen,  but I didn't tweet much yet.  In this presentation, first we will see the definition of system version temporal table,  and how it differs from other temporal table kind.  And then we will see the application of it.  In PostgreSQL, we have at least two options to implement system version table.  One is using two table for storing, one for current data, and the other one for history  data.  Another alternative is using one table for storing both current and history card.  I will talk about both options and the advantage of implementing it using one table approach.  Finally, we will talk about using syntax and their function that system version temporal  table will introduce.  System version temporal table is introduced to SQL standard along with application time  period and other temporal specification in 2011 release.  It is about the retention of deleted record along with current one automatically by database  management system and the ability of creating both current and history record.  And there are application time period which are for meeting business model, having time  varying information, and it is managed by user rather than by database system.  And it is legal to have both system version and application time period in a single table.  We can use system version temporal table for that sake of easily recovering from accidental  data modification.  If we enable system versioning to the table, we can go back to any point in time using  SQL query.  We can also use it for auditing to check how things look like in the past.  And other interesting use cases to model reality in place of application time period.  If model reality changes at the same time with database modification, we can use system  version temporal table because it have advantage of maintaining by the system automatically.  We can also use it to analyze how things look like over time.  In post-release SQL, we have at least two design for implementing system version temporal  table.  One is on wiki page that describe implementing using two tables.  One for history data and the other for current data.  But I don't go with this approach because I don't know why I feel in most parts.  I propose to implement it using only one table for storing both current and history record.  And it is on current commit feast.  I will talk about both approach and I describe more on my approach and its advantage.  Two table approach involves two tables.  One for current data storage and the other for history data.  One big advantage of this approach is non temporal query which are the frequent query  performance didn't affect by history data because it's only access current table.  But nowadays we can achieve similar performance by partitioning.  And in this approach all the record generated by delay and update operation inserted to  history table using trigger and multiple common have to create implicitly to make correlation  between current and history record.  In one table approach both current and history data stores in one table.  It uses end time column and value to classify the record.  If the value is infinity it is current record.  Otherwise it's related at a specified time in the time column.  And system version the table treats like a kind of generated column in its implementation.  Because the syntax is similar and generated column passed the test of time and the result  of non temporal query doesn't have to include or consider history record.  So filter codes will be added to such kind of query implicitly.  There are two create system version table.  There are two option to create system version table.  If it is okay to use default system version in column names.  Just adding with system version keyword at the end of table definitions.  Enough.  It enables system versioning with default system versioning column name.  But if you wanted to use different name for system versioning column name we have to use  X standard option as specified on the screen.  Stay two time stamp with time zone column with generated always as the start and end  time specification.  In my implementation both current and history data stores in one table.  But it's perfectly legal to have multiple record having the same primary and unique key  value in the past.  The conisterant only have to be observed on current data or current records.  And in order to allow this happen raw in the time column is added to primary and unique  key conisterant implicitly.  Because in current record raw in the time column and values always infinity.  So that force primary and unique key value to be unique across current record.  But in history record raw in the time column and values different.  So primary and unique key value can be repeated.  In that system versioning column set automatically.  Raw start time will be set to current transaction time.  And raw end time column will be set to infinity.  Here there are opinion on the appropriateness of setting raw end time column value to infinity.  If we take this value literally it means raw will be current until infinity.  But it's not true.  The record will be removed sometimes before infinity.  More meaningful values to store variable now.  Which have the meaning the meaning data is current until now.  But which I think it is more appropriate value.  But storeable now variable didn't exist.  So even SQL standard stay to use longest date data type value.  In postgres SQL it is infinity.  Normally update didn't occur in place.  So it's performed by marking the tuple to be update to delete.  That can be actually removed by other process.  And then insert the updated tuple into the table.  But for system versioned temporal table implementation delete tuple will be inserted back with raw  end time column value set to current transaction time.  Not make the record history record and insert the updates tuple by making it counter-recount  by setting raw start time column value to current transaction time and end time column  value to infinity.  In delete the record didn't actually removed.  Instead it's inserted back with raw end time column value set to current transaction time.  Not in the record being current record.  In select non temporal carry should not incorporate or consider history record.  So history data filter close added to it implicitly.  Advantage of one table approach.  Well table is not any complex than non temporal table alter operation.  But in two table approach modification in current table should have to propagate to history  table and other advantages there is no need of technical column to correlate between history  and current data.  And if we support implicit updates for marking deleted tuple as a history data we can enjoy  many optimization.  Because there will be no need of vacuum exit for freezing and the data will be stored sorted  by raw start and end time column automatically.  So we can harness multiple optimization for temporal query processing on this behavior.  The first form of temporal query is for system time as of close.  It is used when there is a need to see the table at specified point in time in the past.  It returns all the record current at specified point in time which means column and value  less than specified point in time and which means raw start time column and value less  than specified point in time and raw end time column and value greater or equal to specified  point in time value will be returned and the syntax is specified on the screen.  The other form is form close which returns all the record current within specified time  rate including time point one that's excluding time point two.  In closing it is the same as form close except it includes the record current at time point  two.  So it is the only difference from closes.  It includes in time point two its return value.  Between asymmetric closes is the same as between symmetric or between close.  It is just more descriptive and between symmetric close here the order of time point specification  is not matter because it work by picking the least time point and return the record up  to and including the greater time point.  There are a new syntax introduced to enable system versioning to existing table which  is alter table add system versioning.  It use default system versioning column and name and if the table content data it will  be marked to current data by setting raw start time column and value to current transaction  time and or in the time column value to infinity.  If we want to use different column and name for system versioning we can do it by issuing  add column and statement to raw start and end time column with the desired column and  name in one command as seen on the screen.  But it is forbidden to issue add column and command separately because it leaves system  versioning in unusable state.  If we want to if we don't want system versioning number or if we want to delete history data  up to now we can issue drop system versioning to the table that drop system versioning column  along with history data.  We can use it with add system versioning command to limit the growth of system version  table.  And here are other alternative command to disable system versioning.  So if anyone want to look at the patch and review it is on current commit fist please  review if possible.  Thanks.
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